1120 lines
49 KiB
Markdown
1120 lines
49 KiB
Markdown
# CDROM Video CDs (VCD)
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VCDs are Video CDs with MPEG compression, yielding a playtime of 72 minutes per
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disc (whole movies usually being stored on two CDs). VCDs are popular in asia
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(as opposed to VHS tapes used in western world).<br/>
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#### VCDs on Playstation
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For the Playstation, the asian SCPH-5903 model includes a special daughterboard
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with MPEG decoding hardware for playing VCDs.<br/>
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[CDROM - Video CD Commands](cdromdrive.md#cdrom-video-cd-commands)<br/>
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[Pinouts - VCD Pinouts](pinouts.md#pinouts-vcd-pinouts)<br/>
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Without that hardware it has been widely believed to be impossible to play VCDs
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on Playstations, although, as of 2017, it turned out that the Playstation's CPU
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and MDEC decoder are fast enough for that purpose (when skipping B-frames,
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rendering the movie in monochrome without colors, and reducing audio output to
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11kHz/mono).<br/>
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#### ISO Filesystem (Track 1)
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[VCD ISO Basic Files (INFO, ENTRIES, AVSEQnn, ISO Filesystem)](cdromvideocdsvcd.md#vcd-iso-basic-files-info-entries-avseqnn-iso-filesystem)<br/>
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[VCD ISO Playback Control PBC Files (PSD, LOT, ITEMnnnn)](cdromvideocdsvcd.md#vcd-iso-playback-control-pbc-files-psd-lot-itemnnnn)<br/>
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[VCD ISO Search Files (SCANDATA, SEARCH, TRACKS, SPICONTX)](cdromvideocdsvcd.md#vcd-iso-search-files-scandata-search-tracks-spicontx)<br/>
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[VCD ISO Misc files (CAPTnn, AUDIOnn, KARINFO, PICTURES, CDI)](cdromvideocdsvcd.md#vcd-iso-misc-files-captnn-audionn-karinfo-pictures-cdi)<br/>
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#### MPEG Streams (Track 2 and up)
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[VCD MPEG-1 Multiplex Stream](cdromvideocdsvcd.md#vcd-mpeg-1-multiplex-stream)<br/>
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[VCD MPEG-1 Video Stream](cdromvideocdsvcd.md#vcd-mpeg-1-video-stream)<br/>
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XXX MPEG-1 Macroblocks<br/>
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[VCD MP2 Audio Stream](cdromvideocdsvcd.md#vcd-mp2-audio-stream)<br/>
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#### VCD Versions & Variants
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XXX<br/>
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## VCD ISO Basic Files (INFO, ENTRIES, AVSEQnn, ISO Filesystem)
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#### Primary Volume Descriptor (00:02:16)
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VCDs are having a standard ISO Primary Volume Descriptor, with some VCD
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specific entries:<br/>
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```
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008h 32 System Identifier (always "CD-RTOS CD-BRIDGE" for VCDs)
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028h 32 Volume Identifier (often nonsense, eg. "" or "__" or "VolumeLabel")
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23Eh 128 Application Identifier ("CDI/CDI_APPL.VCD;1" or "CDI/CDI_VCD.APP;1")
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400h 8 CD-XA Identifying Signature ("CD-XA001" for PSX and VCD)
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```
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There are some more differences to normal CDROMs:<br/>
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```
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VCDs are using MODE2 (with 800h-byte and 914h-byte sectors)
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MPEG videos are on extra data tracks (outside of the ISO area on Track 1)
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Files in VCD or SVCD folders use fixed sectors numbers (00:04:00 and up)
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All 16bit/32bit values in files in VCD,SVCD,EXT,etc are BIG-ENDIAN
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```
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Due to the fixed sector numbers, VCDs players can completely ignore the ISO
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filesystem with filenames and folders, and just address everything via sector
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numbers (though accessing files in EXT and CDI folders seem to require using
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the filesystem).<br/>
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#### VCD\INFO.VCD or SVCD\INFO.SVD (00:04:00) (800h bytes, one sector)
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```
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000h 8 ID "VIDEO_CD" for VCD (or "SUPERVCD"/"HQ-VCD " for SVCD)
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008h 1 Version ;Version Major (01h) (or 02h for VCD 2.0)
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009h 1 System Profile Tag ;Version Minor (00h) (or 01h for VCD 1.1 or HQ)
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00Ah 16 Album ID/Desc (name in ASCII, padded with SPC) (usually empty)
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01Ah 2 Total Number of CDs in Album (1..N) ;\usually always 1,1 (even
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01Ch 2 Number of this CD in Album (1..N) ;/for movies with 2 discs)
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01Eh 13 PAL Flags, 98x1bit, for each Track? (0=NTSC, 1=PAL)
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02Bh 1 InfoStatusFlags (see below)
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Below is usually zero-filled when not using PBC
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02Ch 4 Size of PSD.VCD file (or PSD.SVD?) (0=None)
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030h 3 First segment addr MM:SS:00 in BCD (00:02:00 ???)
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033h 1 Offset Multiplier for "PsdOffset" values in PSD.VCD (must be 8)
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034h 2 Number of ListIDs in LOT.VCD file (1..7FFFh, plus 1 in some discs)
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036h 2 Number of ITEMnnnn.DAT files (plus nonsense in some discs?)
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Below is usually zero-filled (maybe exists on SVCD only?)
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038h 1980 SegmentContent[1..1980] (b0-1=Audio, b2-4=Video, b5=Cont, b6-7=OGT)
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7F4h 5*2 volume start time[0]: 5x16bit ;aka playing_time[5] in seconds (?)
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7FEh 2 Reserved (0)
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```
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InfoStatusFlags at [02Bh] describes certain characteristics of the disc:<br/>
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```
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bit0 Reserved, must be zero
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bit1-2 Restriction (0=No, 1..3=Restricted category 1..3) (eg. "not for kids")
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bit3 Special Information is encoded in the pictures, uh?
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bit4 MPEG User Data is used for Closed Caption (user_data_cc) (0=No, 1=Yes)
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bit5 Next Disc with PBC (0=Start at ListID#1, 1=Start at ListID#2)
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bit6 Next Disc without PBC (0=Start at Track #2, 1=Start at Track #3)
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bit7 Extended PBC available (0=No, 1=Yes... aka EXT\PSD_X exists?)
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```
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Note: Bit5/6 are used only if the next disc has the same Album ID (eg. the
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feature allows to skip copyright messages if the same message was already shown
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on another disc).<br/>
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First\_segment\_addr: The location of the first sector of the Segment Play Item
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Area [that is... the first ITEMnnnn.DAT file?], in the form mm:ss:00. Must be
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00:00:00 if PSD size is zero. If PSD size is nonzero, but no segments used:
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Usually set to 00:02:00.<br/>
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#### VCD\ENTRIES.VCD or SVCD\ENTRIES.SVD (00:04:01) (800h bytes, one sector)
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```
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000h 8 ID "ENTRYVCD" for VCD and SVCD (or "ENTRYSVD" for VCD30)
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008h 1 Version ;\same as in INFO.VCD/SVD
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009h 1 System Profile Tag ;/
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00Ah 2 Number of Entries/Chapters (1..500)
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00Ch 4*500 Entry[N] (Track 02h..99h, and MM:SS:FF) (all 4 bytes in BCD)
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7DCh 36 Reserved (0)
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```
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Version;<br/>
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```
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0x02 --- VCD2.0
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0x01 --- SVCD, should be same as version in INFO.SVD
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```
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Sys\_prof\_tag;<br/>
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```
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0x01 if VCD1.1
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0x00 else
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```
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#### MPEGAV\AVSEQnn.DAT (pointers to max 98 MPEG-1 Tracks, nn=01..98) (for VCDs)
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#### MPEG2\AVSEQnn.MPG (pointers to max 98 MPEG-2 Tracks, nn=01..98) (for SVCDs)
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#### MPEGAV\AVSEQnn.MPG (pointers to WHATEVER) (as so on some SVCDs or VCD30?)
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These filesystem entries contain pointers to the video tracks (that is, outside
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of the ISO area on Track 1).<br/>
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Commercially made SVCDs can reportedly contain 7 folders: Autorun, Data, Ext,
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Mpegav, Segment, Svcd and Vmp (ie. there's no MPEG2 folder on all SVCDs? though
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that MPEGAV folder is said to contain a .MPG file instead of .DAT file).<br/>
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## VCD ISO Playback Control PBC Files (PSD, LOT, ITEMnnnn)
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Playback Control (PBC) is an optional feature that allows to define menues,
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pictures or text pages (whereas all those is internally just consisting of MPEG
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compressed bitmaps; rather than of text characters).<br/>
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Presence of the PBC feature is indicated by PSD.VCD filesize entry (in
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INFO.VCD) being nonzero. PBC seems to be supported by most VCDs (except older
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discs from around 1997), however, many VCDs are merely including a single
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PlayList entry for the movie track, without any further menues/extras.<br/>
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#### VCD\PSD.VCD or SVCD\PSD.SVD (00:04:34 and up) (max 256 sectors)
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The Descriptors in this file can be considered as being "program code". The
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program is usually stuck on "executing" the current descriptor (eg. playing a
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movie, or showing a selection menu) without automatically increasing the
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program counter. Actual program flow occurs only if the user presses a button
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(or upon selection timeouts), causing the program to "goto" to a new PsdOffset.
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And, something does probably happen upon end-of-track/item... maybe that does
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automatically trigger the Next button handler?<br/>
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```
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<B> PsdPlayListDescriptor (14+2*N bytes):</B>
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00h 1 Type (10h=PlayList)
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01h 1 Number of Items (noi) ;for Start-of-Movie and Numeric-Input?
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02h 2 ListID for this Descriptor (1..7FFFh)
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04h 2 PsdOffset for Prev button (FFFFh=Disable)
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06h 2 PsdOffset for Next button (FFFFh=Disable)
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08h 2 PsdOffset for Return/back button (FFFFh=Disable)
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0Ah 2 Play time in 1/15s (=max 72.8 minutes) (or 0000h=full item)
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0Ch 1 Delay time in "1s/10s" units after ;<-- uh, after? after what?
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0Dh 1 Auto pause time in "1s/10s" units (used for each item in list if
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the auto pause flag in a sector is true) [WHAT is that? Trigger bit?]
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0Eh 2*N ItemID[N] ;item number (0..599 or 1000..2979)
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Entry 0 is for "start of movie" (usually 0002h=Track 2)
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Entry 1..N-1 is for numeric input ?
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<B> PsdSelectionListDescriptor (20+2*N bytes, or 36+6*N bytes):</B>
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00h 1 Type (18h=SELECTION_LIST, or 1Ah=EXT_SELECTION_LIST)
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01h 1 Flags (bit0=SelectionArea, bit1=CommandList, bit2-7=Reserved)
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02h 1 nos <-- aka Number of Numeric-input selections ?
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03h 1 bsn <-- ?
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04h 2 ListID for this Descriptor (1..7FFFh)
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06h 2 PsdOffset for Prev button
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08h 2 PsdOffset for Next button
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0Ah 2 PsdOffset for Return/back button
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0Ch 2 PsdOffset for Default button (uh, what is that?)
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0Eh 2 PsdOffset for Timeout
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10h 1 totime <-- aka Timeout Time maybe? in WHAT units?
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11h 1 loop <-- aka ?
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12h 2 itemid <-- aka Item to be displayed during the selection?
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14h 2*N PsdOffset[N] for Numeric-input ?
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Below only for SVCDs (with Type=18h), or for Extended VCDs (with Type=1Ah):
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(14h+2*N) 4 Area for Prev (x1,y1,x2,y2) ;\these extra entries exist for
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(18h+2*N) 4 Area for Next (x1,y1,x2,y2) ; SVCDs with Type=18h, and
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(1Ch+2*N) 4 Area for Return (x1,y1,x2,y2) ; Extended VCDs with Type=1Ah
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(20h+2*N) 4 Area for Default (x1,y1,x2,y2) ; (but do NOT exist for
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(24h+2*N) 4*N Area[N] (x1,y1,x2,y2) ;/older VCDs with Type=18h)
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<B> PsdEndListDescriptor (8 bytes)</B>
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00h 1 Type (1Fh=EndList)
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01h 1 Next_disc ;00h to stop PBC or NNh to switch to disc no NN (BCD!?)
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02h 2 Item (0 or 1000..2979, should be still image, eg. Change Disc pic)
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04h 4 Reserved (0)
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N/A - This descriptor doesn't have a ListID (unlike as other descriptors)
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<B> PsdCommandListDescriptor (5+2*N bytes)</B>
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00h 1 Type (20h=CommandList)
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01h 2 Command_count
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03h 2 ListID for this Descriptor (1..7FFFh)
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05h 2*N command[EMPTY_ARRAY_SIZE] ;uh, WHAT is a command?
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<B> PsdAlignmentPadding (after each list entry)</B>
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00h 0..7 Padding to next 8-byte PsdOffset boundary (00h-filled)
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```
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Delay values in "1s/10s" units (for PlayList[0Ch,0Dh]):<br/>
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```
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1..60 --> wait "N" seconds
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61..254 --> wait "(N-60)*10+60" seconds
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255 --> wait infinite
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```
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Item numbers (0..599 or 1000..2979) can be:<br/>
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```
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0..1 - Play nothing
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2..99 - Play Track 2..99 (TOC tracks, for AVSEQnn.DAT and AUDIOnn.DAT?)
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100..599 - Play Entry 1..500 from table in ENTRIES file up to end of track
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600..999 - Reserved
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1000..2979 - Play SPI Segment Play Item 1..1980 (ITEMnnnn.DAT file)
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2980..65535 - Reserved
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```
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PsdOffset values can be:<br/>
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```
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0..N Offset within PSD.VCD file, in 8-byte units
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FFFDh PSD_OFS_MULTI_DEF_NO_NUM ;\uh, what is that?
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FFFEh PSD_OFS_MULTI_DEF ;/
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FFFFh PSD_OFS_DISABLED ;-no function assigned to the button
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```
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For whatever reason, some PsdOffsets are specified as ListID (lid), these
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ListID values must be translated to actual PsdOffset via the ListID Offset
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Table (aka LOT.VCD/LOT.SVD file).<br/>
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#### VCD\LOT.VCD or SVCD\LOT.SVD (00:04:02..33) (64Kbyte, 32 sectors)
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The ListID Offset Table (LOT) allows to translate ListIDs to PsdOffsets. The
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file is always 64Kbyte in size (unused entries should be set to FFFFh).<br/>
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The PSD.VCD file does also assign ListIDs to each descriptor (ie. instead of
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using the LOT.VCD file, one could also scan all descriptors in PSD.VCD when
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searching a specific ListID).<br/>
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```
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0000h 2 Reserved (0)
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0002h 2*7FFFh PsdOffset[1..7FFFh] ;for ListID 1..7FFFh
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```
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Note: ListID#1 is used as entrypoint to PSD.VCD when inserting a new disc (or
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when inserting another disc of the SAME movie, the entrypoint can be ListID#2,
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depending on the Next Disc flag in INFO.VCD).<br/>
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#### SEGMENT\ITEMnnnn.DAT (Pictures, Menu screens) (nnnn=0001..1980)
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These files contain Pictures/Menu screens referenced from PSD.VCD. The files
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seem to be stored in FORM2 sectors (not FORM1). Unknown if the files are
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located on Track 1.<br/>
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The content of the files seems to resemble short MPEG video clips (with only
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one picture frame, or eventually with a few frames for short animations,
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including audio in some cases). Still images are said to be allowed to use
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twice the resolution of MPEG videos.<br/>
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#### EXT\PSD\_X.VCD or EXT\PSD\_X.SVD (extended version of PSD.VCD)
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#### EXT\LOT\_X.VCD or EXT\LOT\_X.SVD (extended version of LOT.VCD)
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The "extended" files are often identical to the normal PSD/LOT files. The
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difference is that, if disc uses SelectionLists, then PSD should use the normal
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descriptor (18h), and PSD\_X should use the extended descriptor (1Ah), the
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latter one seems to be intended to allow to highlight the current menu
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selection (particulary useful when using +/- buttons instead of Numeric Keypad
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input). Note: Nethertheless, Muppets from Space uses descriptor 18h in PSD\_X.<br/>
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Unknown if SVCDs do really have "extended" files, too (theoretically the VCD
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extension should be a default feature for SVCDs).<br/>
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#### Playback Control Issues
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Although PBC was intended as "nice extra feature", many VCDs are containing
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faulty PSD files. In general, VCD players should either leave PBC unsupported
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(or provide an option for disabling it).<br/>
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Red Dragon from 2003 uses extended selection lists, but crops PSD\_X.VCD to the
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same filesize as PSD.VCD.<br/>
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Muppets from Space from 1999 assigns weird functions to Prev/Next buttons (Next
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wraps from Last Track to First Track, but Prev doesn't wrap from First to Last;
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default Non-PBC Prev/Next functions are more user friendly).<br/>
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Sony's SCPH-5903 console refuses to display the HH:MM:SS playback time when
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using PBC (instead it does only display a "PBC" logo).<br/>
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## VCD ISO Search Files (SCANDATA, SEARCH, TRACKS, SPICONTX)
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Below files can help searching I-frames, and provide some info about the
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content of Tracks and Segments.<br/>
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Essentially, searching I-frames is possible without these files - however, if
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present, then the files may be useful in two cases: For discs with variable
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bitrates (which isn't allowed on VCDs though), and, for CDROM firmwares that
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don't support "inaccurate" seeking (like telling it to start reading anywhere
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NEAR some MM:SS:FF value, so one could skip sectors till reaching an I-frame)
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(ie. if the firmware insists on a "accurate" seek position, then it's best to
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give it a known I-frame address).<br/>
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#### Caution: Overlapping Sectors (!?!)
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Reportedly the new SVCD files TRACKS.SVD and SEARCH.DAT are on these sectors:<br/>
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```
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TRACKS_SVD_SECTOR = (PSD_VCD_SECTOR+1) ;aka 2nd sector in PSD.SVD?
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SEARCH_DAT_SECTOR = (TRACKS_SVD_SECTOR+1) ;aka 3rd..Nth sector in PSD.SVD?
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```
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If that's correct, then the files would overlap with PSD.SVD (when PSD.SVD is
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bigger than one sector), that would be weird, but possible (ie. the "PsdOffset"
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in PSD.SVD would need to "skip" the region used by those two files).<br/>
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#### EXT\SCANDATA.DAT (12+3\*N bytes for VCD 2.0) (or 16+3\*N+2\*X+3\*Y+3\*Z for SVCD)
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This file fulfills much the same purpose of the SEARCH.DAT file except that
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this file is mandatory only if the System Profile Tag of the INFO.SVD file is
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0x01 (HQ-VCD) and also that it contains sector addresses also for each video
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Segment Play Items in addition to the regular MPEG tracks.<br/>
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```
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SCANDATA.DAT Format for VCD 2.0 (12+3*N bytes):
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000h 8 ID "SCAN_VCD"
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008h 1 Version (02h for VCD 2.0)
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009h 1 Reserved (0)
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00Ah 2 Number of scan points (in 0.5s units) (max FFFFh = ca. 9.1 hours)
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00Ch 3*N Scan Point[0..N-1] ;MM:SS:FF of closest I-frame
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SCANDATA.DAT Format for SVCD (16+3*N+2*X+3*Y+3*Z bytes):
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000h 8 ID "SCAN_VCD"
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008h 1 Version (01h for SVCD)
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009h 1 Reserved (0)
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00Ah 2 scandata_count ;number of 3-byte entries in the table
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00Ch 2 track_count ;number of MPEG tracks on disc
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00Eh 2 spi_count ;number of consecutively recorded play item segments
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; (as opposed to the number of segment play items).
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010h 3*N msf_t cum_playtimes[N] ;cumulative playing time up to track N.
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; (track time just wraps at 99:59:74)
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xxxh 2*X spi_indexes[X] ;Indexes into the following scandata table
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xxxh 2 mpegtrack_start_index ;Index into the following scandata table
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; (where the MPEG track scan points start)
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xxxh 3*Y The scandata table... [Y] ;8bit Track Number and 16bit Index
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uint8_t track_num; /* Track number as in TOC
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uint16_t table_offset; /* Index into scandata table
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xxxh 3*Z msf_t scandata_table[Z] ;MM:SS:FF
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```
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#### SVCD\SEARCH.DAT (13+3\*N bytes)
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This file defines where the scan points are. It covers all mpeg tracks
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together. A scan point at time T is the nearest I-picture in the MPEG stream to
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the given time T. Scan points are given at every half-second for the entire
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duration of the disc.<br/>
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```
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000h 8 ID "SEARCHSV"
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008h 1 Version (01h)
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009h 1 Reserved (0)
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00Ah 2 Number of scan points
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00Ch 1 Time_interval (in units of 0.5 seconds) (must be 01h)
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00Dh 3*N Scan Point[0..N-1] ;MM:SS:FF of closest I-frame
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```
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Note: This SVCD file is about same as the old EXT\SCANDATA.DAT file on VCDs
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(with one extra entry for Time Interval). Whilst, SVCDs are storing some
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different stuff in EXT\SCANDATA.DAT (despite of the identical filename).<br/>
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#### SVCD\TRACKS.SVD (11+4\*N bytes) (or rarely:11+5\*N bytes)
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The TRACKS.SVD file contains a series of structures, one for each track, which
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indicates the track's playing time (in sectors, not actually real time) and
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contents.<br/>
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SVCD\TRACKS.SVD is a mandatory file which describes the numbers and types of
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MPEG tracks on the disc.<br/>
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```
|
|
SVCD\TRACKS.SVD Format for SVCD (11+4*N bytes):
|
|
000h 8 ID "TRACKSVD"
|
|
008h 1 Version (01h)
|
|
009h 1 Reserved (0)
|
|
00Ah 1 Number of MPEG tracks (N)
|
|
00Bh 3*N Track playing_time[N] (MM:SS:FF, in BCD)(in sectors, not real time)
|
|
0xxh 1*N TrackContent[N] ;bit0-1=Audio,bit2-4=Video,bit5=Reserved,bit6-7=OGT
|
|
SVCD\TRACKS.SVD Format for VCD30 (11+5*N bytes) (some sort of SVCD-prototype):
|
|
000h 8 ID "TRACKSVD"
|
|
008h 1 Version (01h)
|
|
009h 1 Reserved (0)
|
|
00Ah 1 Number of MPEG tracks (N)
|
|
00Bh 5*N Cum_Playing_time and Content (MM:SS:FF in BCD, and OGT, Audio)
|
|
```
|
|
|
|
#### SVCD\SPICONTX.SVD (1000h bytes, two sectors)
|
|
Unknown if/when/where/why this file exists, possibly only on VCD30?<br/>
|
|
Note: The same info can be stored in INFO.SVD at offsets [038h..7F3h].<br/>
|
|
```
|
|
0000h 8 ID "SPICONSV"
|
|
0008h 1 Version (01h)
|
|
0009h 1 Reserved (0)
|
|
000Ah 2*1980 Segment Content[1..1980] (1st byte=OGT, 2nd byte=Audio)
|
|
0F82h 126 Reserved (0)
|
|
```
|
|
|
|
#### Content Flags for Segments and Tracks
|
|
For SVCD\INFO.SVD and SVCD\TRACKS.SVD (on SVCD) these are encoded in 1 byte:<br/>
|
|
```
|
|
bit0-1 Audio characteristics:
|
|
0 = No MPEG audio stream
|
|
1 = One MPEG1 or MPEG2 audio stream without extension
|
|
2 = Two MPEG1 or MPEG2 audio streams without extension
|
|
3 = One MPEG2 multi-channel audio stream with extension
|
|
bit2-4 Video characteristics:
|
|
In TRACKS.SVD this must be 0,3,7 (no still pictures)
|
|
0 = No MPEG video data
|
|
1 = NTSC still picture
|
|
2 = NTSC Reserved (NTSC still pic hires?)
|
|
3 = NTSC motion picture
|
|
4 = Reserved
|
|
5 = PAL still picture
|
|
6 = PAL Reserved (PAL still pic hires?)
|
|
7 = PAL motion picture
|
|
bit5 Indicates segment is continuation of an item
|
|
In TRACKS.SVD this must be 0 (reserved)
|
|
0 = First or only segment of item
|
|
1 = Second or later segment of item
|
|
bit6-7 Overlay Graphics/Text (OGT):
|
|
0 = No OGT substream
|
|
1 = Sub-stream 0 available
|
|
2 = Sub-stream 0 & 1 available
|
|
3 = All OGT sub-substreams available
|
|
```
|
|
For SPICONTX.SVD and SVCD\TRACKS.SVD (on VCD30) these are encoded in 2 bytes:<br/>
|
|
```
|
|
1st byte = Audio characteristics ;\probably same values as
|
|
2nd byte = Overlay Graphics/Text (OGT) ;/in above bitfields?
|
|
```
|
|
|
|
|
|
|
|
## VCD ISO Misc files (CAPTnn, AUDIOnn, KARINFO, PICTURES, CDI)
|
|
#### EXT\CAPTnn.DAT (Closed Caption data, aka subtitles) (SVCD only?)
|
|
VCDs with subtitles are usually/always having the subtitles encoded directly in
|
|
the picture frames (ie. in the MPEG macroblocks, rather than using the Closed
|
|
Caption feature).<br/>
|
|
These CAPTnn.DAT files are intended for Closed Captions (eg. subtitles in
|
|
different languages and/or for deaf people).<br/>
|
|
Alternately, the "user\_data\_cc" flag in INFO.VCD?/INFO.SVD can indicate to
|
|
store Closed Captions in MPEG User Data (with START\_CODE=000001B2h=User Data)
|
|
instead of in EXT\CAPTnn.DAT. Either way, the format of those Closed Captions
|
|
is unknown.<br/>
|
|
Moreover, Content can be flagged to have Overlay Graphics/Text (OGT), whatever
|
|
that is: it might be related to Closed Captions.<br/>
|
|
Note: Reportedly CAPTnn.DAT can exist on VCDs and SVCDs (although the same
|
|
person reported that VCDs do not support subtitles, so that info sounds wrong).<br/>
|
|
|
|
#### CDDA\AUDIOnn.DAT (pointers to uncompressed CD Audio Tracks)
|
|
These filesystem entries contain pointers to uncompressed audio tracks tracks
|
|
(that is, outside of the ISO area on Track 1).<br/>
|
|
Most VCDs don't have audio tracks (though some VCDs do contain empty CDDA
|
|
folders).<br/>
|
|
Maybe the feature is occassionally used the other way around: Music discs
|
|
containing VCD clips as bonus feature?<br/>
|
|
|
|
#### KARAOKE\KARINFO.xxx (whatever)
|
|
The KARAOKE folder exists on many VCDs (about 50%), but it's usually/always
|
|
empty on all discs.<br/>
|
|
Reportedly the folder can contain "KARINFO.xxx" files, but the purpose/format
|
|
of that files is unknown.<br/>
|
|
Reportedly there are Midi VCDs (MVCDs) for karaoke, maybe those discs have
|
|
"KARINFO.xxx" files(?)<br/>
|
|
|
|
#### PICTURES\\*.\* (whatever)
|
|
Unknown purpose. The PICTURES folder has been spotted on one VCD (Wallace and
|
|
Gromit), but the folder was just empty.<br/>
|
|
|
|
#### CDI\\*.\* (some kind of GUI/driver for Philips CDI Players)
|
|
The CDI folder is some relict for Philips CDI Players, it isn't used by normal
|
|
VCD players, however, the CDI folder & files are included on most or all
|
|
VCDs.<br/>
|
|
The path/name for the CDI executable is stored at offset 23Eh in the ISO
|
|
Primary Volume Descriptor (usually "CDI/CDI\_APPL.VCD;1" or "CDI/CDI\_VCD.APP;1")
|
|
(or accidentally "CDI\_CDI\_VCD.APP;1" on homebrew Nero discs).<br/>
|
|
The files in the CDI folder are usually just some standard files (without any
|
|
customizations), however, there are some different revisions of these files:<br/>
|
|
```
|
|
<B> Revision A (spotted on two discs from 1997 and 1999):</B>
|
|
CDI_APPL.VCD 80702 bytes, 04-Mar-1996, CRC32=AE8FC5D0h ;executable
|
|
VCD_BACK.DYV 92572 bytes, 18-Jul-1995, CRC32=00693E5Eh ;whatever?
|
|
VCD_BTN.C8 93719 bytes, 18-Jul-1995, CRC32=FF0A636Ah ;whatever?
|
|
<B> Revision B (spotted on a disc from 2003):</B>
|
|
CDI_VCD.APP 20648 bytes, 00-Nul-0000 CRC32=DC885F70h ;executable
|
|
CDI_FONT.FNT 145388 bytes, 00-Nul-0000 CRC32=FB4D63F4h ;font?
|
|
CDI_ALL.RTF ? bytes, CRC32=? ;realtimefile?
|
|
CDI_BUM.RTF ? bytes, CRC32=? ;realtimefile?
|
|
<B> Revision C (spotted on a disc from 2006, and homebrews from 2001 and 2017):</B>
|
|
CDI_VCD.APP 102400 bytes, 00-Nul-0000 CRC32=E91E128Dh ;executable
|
|
CDI_VCD.CFG 193 bytes, 00-Nul-0000 CRC32=D1C6F7ADh ;config/ascii
|
|
CDI_TEXT.FNT 13616 bytes, 00-Nul-0000 CRC32=BDC55E86h ;font?
|
|
CDI_IMAG.RTF 1510028 bytes, 00-Nul-0000 CRC32=(RIFF) ;realtimefile?
|
|
```
|
|
CDI\_VCD.CFG is some ASCII text file (with uncommon 0Dh,0Dh,0Ah line breaks),
|
|
the file could be customized to change things like GUI colors, but most or all
|
|
discs seem to contain the same file with CRC32=D1C6F7ADh. Note: The CFG file is
|
|
missing on the homebrew DemoVCD.<br/>
|
|
CDI\_IMAG.RTF is seen as 1510028 byte file under windows (that is, with a
|
|
windows RIFF header, and with data area containing the whole 930h bytes from
|
|
each sector; this includes the MM:SS:FF values from the sector header, so the
|
|
RTF file may look slightly different depending on which sectors it has been
|
|
stored on, although the files are usually exactly same apart from those
|
|
MM:SS:FF values). Note: The RTF file is cropped to 1324220 bytes (instead of
|
|
1510028) on the homebrew DemoVCD (apart from that, the file is same as normal).<br/>
|
|
CDI\_ALL.RTF and CDI\_BUM.RTF cannot be read/copied under Windows 7 (which is
|
|
weirdly reporting them to use an "invalid MS-DOS function"; some people also
|
|
reported having CDI\_IMAG.RTF files with similar problems). The reason is
|
|
unknown, maybe windows doesn't fully support the CD filesystem, or some VCDs
|
|
are violating the filesystem specs, or whatever... maybe windows is
|
|
mis-identifying certain RTF files as Rich Text Format files and tries to
|
|
prevent virus-infections by throwing a faked "MS-DOS" error message.<br/>
|
|
|
|
|
|
|
|
## VCD MPEG-1 Multiplex Stream
|
|
#### Multiplex Stream & Sector Boundaries
|
|
The Multiplex stream is some higher level stream, intended to help to
|
|
distinguish between Audio- and Video-streams (which are enclosed in the
|
|
Multiplex stream). MPEG's are somewhat organized in "sectors", with sector size
|
|
varying for normal .mpg files and VCDs:<br/>
|
|
```
|
|
VCD discs --> Sector Size = 914h bytes (the discs MODE2/FORM2 sector size)
|
|
.mpg files --> Sector Size = 800h bytes (regardless of physical sector size)
|
|
```
|
|
Sectors are always beginning with a Multiplex Packet (and Multiplex Packets are
|
|
never crossing sector boundaries). If the amount of video data exceeds the
|
|
sector size, then it's split into several Multiplex packets, whereas, that may
|
|
happen anywhere in the video stream (ie. there can be Multiplex Headers
|
|
occurring even in the middle of Video packet).<br/>
|
|
|
|
#### MPEG-1 Multiplex Pack (sector header) (12 bytes)
|
|
The Pack Header is found at the begin of the stream (on VCDs, it's also found
|
|
at the begin of each sector). The SCR values might help on identifying the
|
|
current playback position, and, with the bitrate value, this could be also used
|
|
to compute the distance to another position (though there are other ways to
|
|
determine the position/bitrate, so the Pack is kinda useless).<br/>
|
|
```
|
|
32bit PACK_START_CODE (000001BAh) ;-4byte
|
|
2bit Fixed (00b for MPEG-1) (would be 01b for MPEG-2) ;\
|
|
2bit Fixed (10b) ;
|
|
3bit System Clock Reference, bit32-30 ;\ ;
|
|
1bit Marker (1) ; System Clock Reference (SCR) ;
|
|
15bit System Clock Reference, bit29-15 ; (intended Time, ; 5byte
|
|
1bit Marker (1) ; in 90kHz clock cycles) ;
|
|
15bit System Clock Reference, bit14-0 ;/ ;
|
|
1bit Marker (1) ;/
|
|
1bit Marker (1) ;\
|
|
22bit Multiplex Rate (total bitrate of the stream, in 400bit/s units) ; 3byte
|
|
1bit Marker (1) ;/
|
|
```
|
|
|
|
#### MPEG-1 Multiplex System Header (12+N\*3 bytes)(optionally)(at start of stream)
|
|
The System Header is usally found after the first Pack at the begin of the
|
|
stream.<br/>
|
|
```
|
|
32bit SYSTEM_HEADER_START_CODE (000001BBh) ;\6byte
|
|
16bit Header Length minus 6 (in bytes) (0006h+N*3) ;/
|
|
1bit Marker (1) ;\
|
|
22bit Rate bound (max multiplex rate of all packs in the stream, ; 3byte
|
|
1bit Marker (1) in 400bit/s units) ;/
|
|
6bit Audio Bound (max number of audio streams in this ISO stream) ;\
|
|
1bit Fixed Flag (1=Fixed bitrate) ; 1byte
|
|
1bit CSPS Flag (1=Constrained) ;/
|
|
1bit System Audio Lock Flag XXX ;\
|
|
1bit System Video Lock Flag XXX ; 1byte
|
|
1bit Marker (1) ;
|
|
5bit Video Bound (max number of video streams in this ISO stream) ;/
|
|
8bit Reserved (FFh) ;-1byte
|
|
```
|
|
Followed by N\*3 bytes for the streams (each with first bit=set):<br/>
|
|
```
|
|
8bit Stream ID (C0h..DFh=Audio, E0h..EFh=Video) ;\
|
|
2bit Fixed (11b) ; 3byte
|
|
1bit STD buffer scale (0=Mul128/audio, 1=Mul1024/video) ;
|
|
13bit STD buffer size (largest required buffer over all packets) ;/
|
|
```
|
|
Terminated by a value with first bit=cleared (eg. next 000001xxh value).<br/>
|
|
|
|
#### MPEG-1 Multiplex Video/Audio/Special Packets (7..24 bytes, plus data)
|
|
These packets are encapsulating the lower-level Video/Audio streams.<br/>
|
|
```
|
|
32bit START (000001xxh BDh-BFh=Special, C0h-DFh=Audio, E0h-EFh=Video);\6byte
|
|
16bit Packet Length minus 6 (in bytes) (1..18, plus data) ;/
|
|
```
|
|
If (and while) next two bits are 11b (0..16 padding bytes):<br/>
|
|
```
|
|
(2bit) Fixed (11b, indicates presence of stuffing) ;\optional 0..16byte
|
|
(6bit) Fixed (111111b) ;/
|
|
```
|
|
If next two bits are 01b (buffer size info):<br/>
|
|
```
|
|
(2bit) Fixed (01b, indicates presence of buffer size) ;\
|
|
(1bit) STD Buffer Scale (0=Mul128/audio, 1=Mul1024/video) ; optional 2byte
|
|
(13bit) STD Buffer Size (for decoding, in above scale units) ;/
|
|
```
|
|
Always:<br/>
|
|
```
|
|
2bit Fixed (00b, indicates no further stuffing/buffer info);\
|
|
1bit PTS Flag (Presentation Time Stamp) ; 0.5 bytes
|
|
1bit DTS Flag (Decoding Time Stamp) ;/
|
|
```
|
|
If PTS Flag set:<br/>
|
|
```
|
|
(3bit) Presentation Time Stamp, bit32-30 ;\
|
|
(1bit) Marker (1) ; optional 4.5 bytes
|
|
(15bit) Presentation Time Stamp, bit29-15 ; (time when to output the
|
|
(1bit) Marker (1) ; the packet to audio/video
|
|
(15bit) Presentation Time Stamp, bit14-0 ; hardware, in 90kHz cycles)
|
|
(1bit) Marker (1) ;/
|
|
```
|
|
If DTS Flag set (in this case PTS Flag must be also set):<br/>
|
|
```
|
|
(4bit) Fixed (0001b) ;\
|
|
(3bit) Decoding Time Stamp, bit32-30 ; optional 5 bytes
|
|
(1bit) Marker (1) ; (recommended time when
|
|
(15bit) Decoding Time Stamp, bit29-15 ; to decode the block,
|
|
(1bit) Marker (1) ; in 90kHz cycles)
|
|
(15bit) Decoding Time Stamp, bit14-0 ;
|
|
(1bit) Marker (1) ;/
|
|
```
|
|
If PTS and DTS Flags are both zero:<br/>
|
|
```
|
|
(4bit) Fixed (1111b) ;-optional 0.5 bytes
|
|
```
|
|
Always:<br/>
|
|
```
|
|
... packet data bytes ;-data...(not crossing sector)
|
|
```
|
|
Note: The first Multiplex Video Packet would usually start with a Sequence
|
|
Header Code (000001B3h), and the first Multiplex Audio Packet should always
|
|
start with an Audio Sync Word (FFFh).<br/>
|
|
However, the size of the Multiplex packets does usually differ from the size of
|
|
the packets in the audio/video stream, so new Multiplex Packets may occur
|
|
anywhere in the middle of those streams (eg. in the middle of a video slice,
|
|
the next Multiplex Video packet would then begin with the remaining slice
|
|
bytes, rather than with a 000001xxh code; it's also possible that a Multiplex
|
|
Audio packet gets inserted in the middle of the video slice).<br/>
|
|
The best (or easiest) way to get continous data for the lower level streams
|
|
might be to memcopy the data from Multiplex packets to separate Audio &
|
|
Video buffers.<br/>
|
|
|
|
#### MPEG-1 Multiplex End Code (4 bytes)
|
|
```
|
|
32bit END_CODE (000001B9h) ;-4byte
|
|
```
|
|
This should occur at the end of the video. On a VCD it does also occur at the
|
|
end of each video track.<br/>
|
|
|
|
|
|
|
|
## VCD MPEG-1 Video Stream
|
|
The Video stream is part of the Multiplex stream, meaning that the Video
|
|
packets preceeded (and interrupted) by Multiplex headers. Ie. before processing
|
|
the Video packets, one must first extract the video snippets from the Multiplex
|
|
stream (see previous chapter).<br/>
|
|
|
|
#### MPEG-1 Video Sequence Header (12, 76, or 140 bytes, ie. 12+N\*64)
|
|
```
|
|
32bit SEQUENCE_HEADER_CODE (000001B3h) ;-4byte
|
|
12bit Width in pixels (1..4095) ;\3byte
|
|
12bit Height in pixels (1..2800, for max AFh slices) ;/
|
|
4bit Aspect Ratio (01h..0Eh, see below) ;\1byte
|
|
4bit Framerate (01h..08h, see below) ;/
|
|
18bit Bitrate (in 400bit/s units, 3FFFFh=variable rate) ;\
|
|
1bit Marker (1) ; 3byte
|
|
10bit VBV (required decoding memory size, in "16 kB" units) ; +6bit
|
|
1bit Constrained Parameter Flag ;/
|
|
1bit Load Intra Q Matrix (0=No, use Standard Matrix, 1=Yes, Custom)
|
|
```
|
|
Next 64byte only when above bit was set:<br/>
|
|
```
|
|
(64byte) Intra Quantizer Matrix (64 x 8bit, unsigned) (in zigzag order)
|
|
1bit Load Non-Intra Q Matrix (0=No, use Standard Matrix, 1=Yes, Custom)
|
|
```
|
|
Next 64byte only when above bit was set:<br/>
|
|
```
|
|
(64byte) Non-Intra Quantizer Matrix (64 x 8bit, unsigned) (in zigzag order)
|
|
```
|
|
Aspect Ratio values:<br/>
|
|
```
|
|
0 - ;forbidden
|
|
1 1.0 ;square pixels
|
|
2 0.6735 ;0.6735
|
|
3 0.7031 ;16:9, 625 line, PAL
|
|
4 0.7615 ;0.7615
|
|
5 0.8055 ;0.8055
|
|
6 0.8437 ;16:9, 525 line, NTSC
|
|
7 0.8935 ;0.8935
|
|
8 0.9157 ;4:3, 625 line, PAL, CCIR601
|
|
9 0.9815 ;0.9815
|
|
10 1.0255 ;1.0255
|
|
11 1.0695 ;1.0695
|
|
12 1.0950 ;4:3, 525 line, NTSC, CCIR601
|
|
13 1.1575 ;1.1575
|
|
14 1.2015 ;1.2015
|
|
15 - ;reserved
|
|
```
|
|
Frame Rate values:<br/>
|
|
```
|
|
0 - ;forbidden
|
|
1 23.976 (24000/1001) ;NTSC encapsulated film rate
|
|
2 24.0 ;Standard international cinema film rate
|
|
3 25.0 ;PAL video frame rate (625/50)
|
|
4 29.97 (30000/1001) ;NTSC video frame rate
|
|
5 30.0 ;NTSC video frame rate drop-frame (525/60)
|
|
6 50.0 ;PAL double frame rate/progressive
|
|
7 59.94 (60000/1001) ;NTSC double frame rate
|
|
8 60.0 ;NTSC double frame rate drop-frame
|
|
9-15 - ;reserved
|
|
```
|
|
|
|
#### MPEG-1 Video Group of Pictures (GOP) (8 bytes) XXX...
|
|
```
|
|
32bit GROUP_START_CODE (000001B8h)
|
|
1bit Drop Frame (1=drop this frame; for reducing 30 fps to 29.97 fps)
|
|
5bit Time Code Hours (0..23)
|
|
6bit Time Code Minutes (0..59)
|
|
1bit Marker (1)
|
|
6bit Time Code Seconds (0..59)
|
|
6bit Time Code Picture (0..59)
|
|
1bit Closed GOP
|
|
1bit Broken Link
|
|
```
|
|
|
|
#### MPEG-1 Video Picture Header XXX...
|
|
```
|
|
32bit PICTURE_START_CODE (00000100h) ;\
|
|
10bit Temporal Reference (display order, 0..3FFh) ; 61bit
|
|
3bit Coding Type (0=Invalid, 1=I, 2=P, 3=B, 4=D, 5-7=Reserved);
|
|
16bit VBV Delay (in 90kHz cycles, FFFFh=variable bitrate) ;/
|
|
```
|
|
If Coding Type is 2 or 3 (P-Frame or B-Frame):<br/>
|
|
```
|
|
(1bit) full fel forward vector (0=half pix, 1=full pix) ;\optional 4bit
|
|
(3bit) forward f code (0=invalid, 1..7=0..6bits) ;/
|
|
```
|
|
If Coding Type is 3 (B-Frame):<br/>
|
|
```
|
|
(1bit) full backward vector ;\optional 4bit
|
|
(3bit) backward f code ;/
|
|
```
|
|
If (and while) next bit is set:<br/>
|
|
```
|
|
(1bit) Fixed (1, indicates presence of Extra Info) ;\opt. N*9bit
|
|
(8bit) Extra Information ;/
|
|
```
|
|
End of Extra:<br/>
|
|
```
|
|
1bit Fixed (0, indicates no further Extra Info) ;-1bit
|
|
0-7bit Padding to byte boundary (0) ;-0..7bit
|
|
```
|
|
Coding Type values:<br/>
|
|
```
|
|
0 Forbidden
|
|
1 I - Intra Coded (full image)
|
|
2 P - Predictive Coded (based on prev I or P frame)
|
|
3 B - Bidirectionally Predictive Coded (based on prev+next I or P frame)
|
|
4 D - DC Intra Coded (don't care, lowres thumbnail)
|
|
5 Reserved
|
|
6 Reserved
|
|
7 Reserved
|
|
```
|
|
|
|
#### Frame Order
|
|
```
|
|
DISPLAY ORDER:
|
|
I B B B P B B B P B B B P B B B I B B B P B B B P B B B P B B B ...
|
|
| |_______|_______| | |_______|_______|
|
|
| | | |
|
|
I-Frame P-frames I-Frame P-frames
|
|
```
|
|
The B-fames require to know the next P- (or I-) frame in advance, for that
|
|
reason, the frames are stored as "PBBB" (although being played as "BBBP"):<br/>
|
|
```
|
|
STORAGE ORDER:
|
|
I P B B B P B B B P B B B I B B B P B B B P B B B P B B B ...
|
|
| |_______|_______| | |_______|_______|
|
|
| | | |
|
|
I-Frame P-frames I-Frame P-frames
|
|
```
|
|
|
|
#### MPEG-1 Video Slice
|
|
Slices are containing the actual 16x16 pixel Macro Blocks. Usually a Slice
|
|
contains one horizontal line - although, theoretically, it could be longer or
|
|
shorter, ie. a slice could wrap to next line, or a line could be split into
|
|
several slices (with the leading "MBA Increment" value greater than 1 to define
|
|
the horizontal start offset).<br/>
|
|
```
|
|
32bit PACK_START_CODE (000001xxh; xx=01h..AFh; vertical index) ;-4byte
|
|
5bit Quantizer Scale (1..31) (may be later changed by blocks) ;-5bit
|
|
```
|
|
If (and while) next bit is set:<br/>
|
|
```
|
|
(1bit) Fixed (1, indicates presence of Extra Info) ;\opt. N*9bit
|
|
(8bit) Extra Information ;/
|
|
```
|
|
End of Extra:<br/>
|
|
```
|
|
1bit Fixed (0, indicates no further Extra Info) ;-1bit
|
|
```
|
|
If (and while) next 23bit are nonzero (ie. until next 000001xxh):<br/>
|
|
```
|
|
... Macroblock (within horizontal line) ;...
|
|
```
|
|
Final padding:<br/>
|
|
```
|
|
0-7bit Padding to byte boundary (0) ;-0..7bit
|
|
```
|
|
|
|
#### MPEG-1 Video Group/Sequence Extension Data (reserved)
|
|
#### MPEG-1 Video User Data (optional)
|
|
```
|
|
32bit START_CODE (000001B2h=User Data, 000001B5h=Extension Data) ;-4byte
|
|
... data (end is signaled by presence of next 000001xxh code) ;-data
|
|
```
|
|
User Data can contain Closed Captions (see flag in VCD\INFO.VCD or
|
|
SVCD\INFO.SVD).<br/>
|
|
User Data contains 11h-byte "Created with Nero" in some homebrew discs.<br/>
|
|
|
|
#### MPEG-1 Video Sequence End Code (4 bytes)
|
|
```
|
|
32bit SEQUENCE_END_CODE (000001B7h) ;-4byte
|
|
```
|
|
|
|
|
|
|
|
|
|
#### MPEG-1 Video 4:2:0 Macroblock
|
|
```
|
|
N*11bit Macroblock_address_increase escape/stuffing codes (if any)
|
|
1..11bit Macroblock_address_increase
|
|
1-6bit Macroblock_type
|
|
5bit Quantizer_scale
|
|
... Motion_vector
|
|
3-9bit Coded_block_pattern
|
|
... Block(i)
|
|
```
|
|
Aka...<br/>
|
|
```
|
|
Addr Incr
|
|
Type
|
|
Motion Vector
|
|
QScale
|
|
CBP
|
|
Block b0 (Y1)
|
|
Block b1 (Y2)
|
|
Block b2 (Y3)
|
|
Block b3 (Y4)
|
|
Block b4 (Cb)
|
|
Block b5 (Cr)
|
|
```
|
|
|
|
|
|
|
|
|
|
## VCD MP2 Audio Stream
|
|
VCD video discs and .mpg movie files are having the MP2 Audio Stream enclosed
|
|
in the Multiplex stream (whilst .mp2 audio files may contain raw MP2 data
|
|
without Multiplex stream).<br/>
|
|
|
|
Each MP2 frame is starting with a FFFh syncword (which is always located on a
|
|
byte boundary). Unfortunately, the value FFFh can also occur anywhere in the
|
|
audio data (eg. a 16bit sample with value 3FFCh).<br/>
|
|
So, when starting mid-stream, one will need some guessing when searching a
|
|
valid syncword. The best method is to compute the frame size (based on the
|
|
supposed frame header), and then to check if supposed frame begins AND ends
|
|
with a sync word. Moreover, one could check for invalid sample rate values in
|
|
the frame header, or invalid "groupings" in the frame's data part.<br/>
|
|
VCDs are conventionally having three audio frames encoded in one CDROM sector,
|
|
so the first syncword can be simply found right after the multiplex packet
|
|
header (though that might differ in some cases: VCD2.0 allows different audio
|
|
bitrates, and a CDROM sector could be theoretically shared for Audio and Video
|
|
data).<br/>
|
|
|
|
#### Overall MP2 Frame Format
|
|
```
|
|
Header (32bit)
|
|
Optional CRC (16bit) (or 0bit if none)
|
|
Allocation Information
|
|
Scale Factor Selector Information
|
|
Scale Factors
|
|
Data
|
|
```
|
|
|
|
#### MP2 Header
|
|
```
|
|
12bit Syncword (FFFh) ;\
|
|
1bit Revision (0=MPEG-2, 1=MPEG-1) ; 2 bytes
|
|
2bit Layer (2=Audio LayerII) ;
|
|
(3=LayerI, 1=LayerIII, r3=reserved) ;
|
|
1bit Protection_bit (1=no crc) ;/
|
|
4bit Bitrate_index (1..14) ;\
|
|
(0=free format, 15=reserved) ;
|
|
2bit Sampling_frequency ; 1 byte
|
|
1bit Padding_bit ;
|
|
1bit Private_bit ;/
|
|
2bit Mode ;\
|
|
2bit Mode_extension (aka bound) ;
|
|
1bit Copyright ; 1 byte
|
|
1bit Original/home ;
|
|
2bit Emphasis ;/
|
|
```
|
|
|
|
#### MP2 Checksum (optional)
|
|
```
|
|
16bit CRC
|
|
```
|
|
|
|
#### Allocation Information
|
|
#### Scale Factor Selector Information
|
|
#### Scale Factors
|
|
#### Data
|
|
```
|
|
XXX...
|
|
```
|
|
|
|
|
|
|
|
## Inflate
|
|
Inflate/Deflate is a common (de-)compression algorithm. In the PSX world, it's
|
|
used by the .CDZ cdrom-image format.<br/>
|
|
|
|
[Inflate - Core Functions](cdromvideocdsvcd.md#inflate-core-functions)<br/>
|
|
[Inflate - Initialization & Tree Creation](cdromvideocdsvcd.md#inflate-initialization--tree-creation)<br/>
|
|
[Inflate - Headers and Checksums](cdromvideocdsvcd.md#inflate-headers-and-checksums)<br/>
|
|
|
|
|
|
|
|
## Inflate - Core Functions
|
|
#### tinf\_uncompress(dst,src)
|
|
```
|
|
tinf_init() ;init constants (needed to be done only once)
|
|
tinf_align_src_to_byte_boundary()
|
|
repeat
|
|
bfinal=tinf_getbit() ;read final block flag (1 bit)
|
|
btype=tinf_read_bits(2) ;read block type (2 bits)
|
|
if btype=0 then tinf_inflate_uncompressed_block()
|
|
if btype=1 then tinf_build_fixed_trees(), tinf_inflate_compressed_block()
|
|
if btype=2 then tinf_decode_dynamic_trees(), tinf_inflate_compressed_block()
|
|
if btype=3 then ERROR ;reserved
|
|
until bfinal=1
|
|
tinf_align_src_to_byte_boundary()
|
|
ret
|
|
```
|
|
|
|
#### tinf\_inflate\_uncompressed\_block()
|
|
```
|
|
tinf_align_src_to_byte_boundary()
|
|
len=LittleEndian16bit[src+0] ;get len
|
|
if LittleEndian16bit[src+2]<>(len XOR FFFFh) then ERROR ;verify inverse len
|
|
src=src+4 ;skip len values
|
|
for i=0 to len-1, [dst]=[src], dst=dst+1, src=src+1, next i ;copy block
|
|
ret
|
|
```
|
|
|
|
#### tinf\_inflate\_compressed\_block()
|
|
```
|
|
repeat
|
|
sym1=tinf_decode_symbol(tinf_len_tree)
|
|
if sym1<256
|
|
[dst]=sym1, dst=dst+1
|
|
if sym1>256
|
|
len = tinf_read_bits(length_bits[sym1-257])+length_base[sym1-257]
|
|
sym2 = tinf_decode_symbol(tinf_dist_tree)
|
|
dist = tinf_read_bits(dist_bits[sym2])+dist_base[sym2]
|
|
for i=0 to len-1, [dst]=[dst-dist], dst=dst+1, next i
|
|
until sym1=256
|
|
ret
|
|
```
|
|
|
|
#### tinf\_decode\_symbol(tree)
|
|
```
|
|
sum=0, cur=0, len=0
|
|
repeat ;get more bits while code value is above sum
|
|
cur=cur*2 + tinf_getbit()
|
|
len=len+1
|
|
sum=sum+tree.table[len]
|
|
cur=cur-tree.table[len]
|
|
until cur<0
|
|
return tree.trans[sum+cur]
|
|
```
|
|
|
|
#### tinf\_read\_bits(num) ;get N bits from source stream
|
|
```
|
|
val=0
|
|
for i=0 to num-1, val=val+(tinf_getbit() shl i), next i
|
|
return val
|
|
```
|
|
|
|
#### tinf\_getbit() ;get one bit from source stream
|
|
```
|
|
bit=tag AND 01h, tag=tag/2
|
|
if tag=00h then tag=[src], src=src+1, bit=tag AND 01h, tag=tag/2+80h
|
|
return bit
|
|
```
|
|
|
|
#### tinf\_align\_src\_to\_byte\_boundary()
|
|
```
|
|
tag=01h ;empty/end-bit (discard any bits, align src to byte-boundary)
|
|
ret
|
|
```
|
|
|
|
|
|
|
|
## Inflate - Initialization & Tree Creation
|
|
#### tinf\_init()
|
|
```
|
|
tinf_build_bits_base(length_bits, length_base, 4, 3)
|
|
length_bits[28]=0, length_base[28]=258
|
|
tinf_build_bits_base(dist_bits, dist_base, 2, 1)
|
|
ret
|
|
```
|
|
|
|
#### tinf\_build\_bits\_base(bits,base,delta,base\_val)
|
|
```
|
|
for i=0 to 29
|
|
bits[i]=min(0,i-delta)/delta
|
|
base[i]=base_val
|
|
base_val=base_val+(1 shl bits[i])
|
|
ret
|
|
```
|
|
|
|
#### tinf\_build\_fixed\_trees()
|
|
```
|
|
for i=0 to 6, tinf_len_tree.table[i]=0, next i ;[0..6]=0 ;len tree...
|
|
tinf_len_tree.table[7,8,9]=24,152,112 ;[7..9]=24,152,112
|
|
for i=0 to 23, tinf_len_tree.trans[i+0] =i+256, next i ;[0..23] =256..279
|
|
for i=0 to 143, tinf_len_tree.trans[i+24] =i+0, next i ;[24..167] =0..143
|
|
for i=0 to 7, tinf_len_tree.trans[i+168]=i+280, next i ;[168..175]=280..287
|
|
for i=0 to 111, tinf_len_tree.trans[i+176]=i+144, next i ;[176..287]=144..255
|
|
for i=0 to 4, tinf_dist_tree.table[i]=0, next i ;[0..4]=0,0,0,0,0 ;\dist
|
|
tinf_dist_tree.table[5]=32 ;[5]=32 ; tree
|
|
for i=0 to 31, tinf_dist_tree.trans[i]=i, next i ;[0..31]=0..31 ;/
|
|
ret
|
|
```
|
|
|
|
#### tinf\_decode\_dynamic\_trees()
|
|
```
|
|
hlit = tinf_read_bits(5)+257 ;get 5 bits HLIT (257-286)
|
|
hdist = tinf_read_bits(5)+1 ;get 5 bits HDIST (1-32)
|
|
hclen = tinf_read_bits(4)+4 ;get 4 bits HCLEN (4-19)
|
|
for i=0 to 18, lengths[i]=0, next i
|
|
for i=0 to hclen-1 ;read lengths for code length alphabet
|
|
lengths[clcidx[i]]=tinf_read_bits(3) ;get 3 bits code length (0-7)
|
|
tinf_build_tree(code_tree, lengths, 19) ;build code length tree
|
|
for num=0 to hlit+hdist-1 ;decode code lengths for dynamic trees
|
|
sym = tinf_decode_symbol(code_tree)
|
|
len=1, val=sym ;default (for sym=0..15)
|
|
if sym=16 then len=tinf_read_bits(2)+3, val=lengths[num-1] ;3..6 previous
|
|
if sym=17 then len=tinf_read_bits(3)+3, val=0 ;3..10 zeroes
|
|
if sym=18 then len=tinf_read_bits(7)+11, val=0 ;11..138 zeroes
|
|
for i=1 to len, lengths[num]=val, num=num+1, next i
|
|
tinf_build_tree(tinf_len_tree, 0, hlit) ;\build trees
|
|
tinf_build_tree(tinf_dist_tree, 0+hlit, hdist) ;/
|
|
ret
|
|
```
|
|
|
|
#### tinf\_build\_tree(tree, first, num)
|
|
```
|
|
for i=0 to 15, tree.table[i]=0, next i ;clear code length count table
|
|
;scan symbol lengths, and sum code length counts...
|
|
for i=0 to num-1, x=lengths[i+first], tree.table[x]=tree.table[x]+1, next i
|
|
tree.table[0]=0
|
|
sum=0 ;compute offset table for distribution sort
|
|
for i=0 to 15, offs[i]=sum, sum=sum+tree.table[i], next i
|
|
for i=0 to num-1 ;create code to symbol xlat table (symbols sorted by code)
|
|
x=lengths[i+first], if x<>0 then tree.trans[offs[x]]=i, offs[x]=offs[x]+1
|
|
next i
|
|
ret
|
|
```
|
|
|
|
#### tinf\_data
|
|
```
|
|
clcidx[0..18] = 16,17,18,0,8,7,9,6,10,5,11,4,12,3,13,2,14,1,15 ;constants
|
|
```
|
|
|
|
```
|
|
typedef struct TINF_TREE:
|
|
unsigned short table[16] ;table of code length counts
|
|
unsigned short trans[288] ;code to symbol translation table
|
|
```
|
|
|
|
```
|
|
TINF_TREE tinf_len_tree ;length/symbol tree
|
|
TINF_TREE tinf_dist_tree ;distance tree
|
|
TINF_TREE code_tree ;temporary tree (for generating the dynamic trees)
|
|
unsigned char lengths[288+32] ;temporary 288+32 x 8bit ;\for dynamic tree
|
|
unsigned short offs[16] ;temporary 16 x 16bit ;/creation
|
|
```
|
|
|
|
```
|
|
unsigned char length_bits[30]
|
|
unsigned short length_base[30]
|
|
unsigned char dist_bits[30]
|
|
unsigned short dist_base[30]
|
|
```
|
|
|
|
|
|
|
|
## Inflate - Headers and Checksums
|
|
#### tinf\_gzip\_uncompress(void \*dest, \*destLen, \*source, sourceLen)
|
|
```
|
|
src_start=src, dst_start=dst ;memorize start addresses
|
|
if (src[0]<>1fh or src[1]<>8Bh) then ERROR ;check id bytes
|
|
if (src[2]<>08h) then ERROR ;check method is deflate
|
|
flg=src[3] ;get flag byte
|
|
if (flg AND 0E0h) then ERROR ;verify reserved bits
|
|
src=src+10 ;skip base header
|
|
if (flg AND 04h) then src=src+2+LittleEndian16bit[src] ;skip extra data
|
|
if (flg AND 08h) then repeat, src=src+1, until [src-1]=00h ;skip file name
|
|
if (flg AND 10h) then repeat, src=src+1, until [src-1]=00h ;skip file comment
|
|
hcrc=(tinf_crc32(src_start, src-src_start) & 0000ffffh)) ;calc header crc
|
|
if (flg AND 02h) then x=LittleEndian16bit[src], src=src+2 ;get header crc
|
|
if (flg AND 02h) then if x<>hcrc then ERROR ;verify header
|
|
tinf_uncompress(dst, destLen, src, src_start+sourceLen-src-8) ;----> inflate
|
|
crc32=LittleEndian32bit[src], src=src+4 ;get crc32 of decompressed data
|
|
dlen=LittleEndian32bit[src], src=src+4 ;get decompressed length
|
|
if (dlen<>destLen) then ERROR ;verify dest len
|
|
if (crc32<>tinf_crc32(dst_start,dlen)) then ERROR ;verify crc32
|
|
ret
|
|
```
|
|
|
|
#### tinf\_zlib\_uncompress(dst, destLen, src, sourceLen)
|
|
```
|
|
src_start=src, dst_start=dst ;memorize start addresses
|
|
hdr=BigEndian16bit[src], src=src+2 ;get header
|
|
if (hdr MOD 31)<>0 then ERROR ;check header checksum (modulo)
|
|
if (hdr AND 20h)>0 then ERROR ;check there is no preset dictionary
|
|
if (hdr AND 0F00h)<>0800h then ERROR ;check method is deflate
|
|
if (had AND 0F000h)>7000h then ERROR ;check window size is valid
|
|
tinf_uncompress(dst, destLen, src, sourceLen-6) ;------> inflate
|
|
chk=BigEndian32bit[src], src=src+4 ;get data checksum
|
|
if src-src_start<>sourceLen then ERROR ;verify src len
|
|
if dst-dst_start<>destLen then ERROR ;verify dst len
|
|
if a32<>tinf_adler32(dst_start,destLen)) then ERROR ;verify data checksum
|
|
ret
|
|
```
|
|
|
|
#### tinf\_adler32(src, length)
|
|
```
|
|
s1=1, s2=0
|
|
while (length>0)
|
|
k=max(length,5552)
|
|
for i=0 to k-1, s1=s1+[src], s2=s2+s1, src=src+1, next i
|
|
s1=s1 mod 65521, s2=s2 mod 65521, length=length-k
|
|
return (s2*10000h+s1)
|
|
```
|