CVD Technical Specifications

What can and cannot be specified

The original C-Cube/consortium CVD specification is not publicly available, and the full text of SJ/T 11196-1998 was not obtained for this research. Almost every published CVD “specification” is therefore inferred from SVCD (Philips SVCD 1.0 / IEC 62107 / the Chinese Super VCD regime) plus the known resolution and subtitle differences. Values below are marked as directly attested for CVD where the 1998 Chinese press or Western tooling documentation says so, and otherwise inherited from the SVCD stack that CVD shares.

Physical disc and sector formats

A CVD is a standard 120 mm CD or CD-R using the CD-ROM XA / CD-i Bridge layout defined in the White Book. Track 1 is Mode 2 Form 1 with an ISO 9660 file system holding the metadata files (INFO, ENTRIES, PSD, LOT, SEARCH, TRACKS) and, optionally, the segment play-item area. Tracks 2 onwards are Mode 2 Form 2 MPEG tracks, one per sequence (up to 98). Form 1 sectors carry 2,048 bytes of user data with EDC and Layer-2 ECC; Form 2 sectors carry 2,324 bytes with EDC but no Layer-2 ECC-about 14% more payload. Guangming Daily’s 3 November 1998 comparison states that CVD and SVCD were “completely identical in physical format and file format, both following the relevant international and national standards.”

Disc anatomy follows the VCDImager description of Super Video CD layout: lead-in and TOC; a mandatory 150-sector pregap; an ISO 9660 track with the Primary Volume Descriptor at LSN 16 and the VCD info area at 00:04:00; an optional segment area of up to 1,980 segments of 150 sectors; then the MPEG Form 2 tracks, each preceded by a pregap of at least 150 sectors; a 150-sector postgap; and the lead-out. CVD players used 2× mechanisms; Guangming Daily associates CVD hardware with a Philips double-speed mechanism and CD7 digital servo, against a Sony double-speed mechanism on the SVCD side in the same comparison.

Capacity, data rate and playing time

The raw 2× figure explains why the combined audio-video ceiling is usually quoted as about 2.7 Mbps (Wikipedia) or 2,778 kbps (technical summaries). The ubiquitous “35-45 minutes per disc” figure is simply CD capacity read at 2×. Longer programmes need lower average VBR rates, typically 1.5-2.0 Mbps for sixty to eighty minutes.

Video and audio parameters

Whether CVD was strictly 352-wide or also allowed 480-wide video is not settled. Western sources define CVD by its 352 width. Guangming Daily says CVD “suits both 1/2 D1 and 2/3 D1” sources while SVCD suited only 2/3 D1. Both claims are kept. Pixels per bit favour CVD: 352×576 is 202,752 pixels per frame against SVCD’s 480×576 at 276,480, so at the same bitrate CVD spends roughly a third more bits per pixel. That is the engineering argument for the format. Marketing-era horizontal resolution claims ranged from “up to 400 lines” (makers, July 1998) and “350-400 lines” (Jinzheng) to “about 280 lines” for early 1/2 D1 discs in a December 1998 Wenzhai Bao piece written from a pro-SVCD framing.

Audio is MPEG-1 Layer II at 44.1 kHz, typically 224 kbps within a 32-384 kbps range inherited from SVCD documentation. Up to two stereo or four mono tracks were marketed for karaoke (vocal/instrumental) or four language dubs. MPEG-2 multichannel 5.1 is allowed in the SVCD family but rarely supported; Guangming Daily notes that a “5.1-channel CVD scheme” had already been announced by November 1998. One AnandTech forum user in 2002 described CVD as “basically an SVCD with 352 × 240 VCD resolution and 48 KHz audio.” Every other source gives 352×480/576 and 44.1 kHz. VideoHelp users report that some players accept 48 kHz on CD and some play it too slowly (a Sony S560D is named). Both strands are kept. For DVD use, 44.1 kHz audio is not legal and must be resampled to 48 kHz.

File system, metadata and MPEG constraints

CVD uses the SVCD directory tree. From the GNU VCDImager manual the important paths are /SVCD/INFO.SVD (system ID “SUPERVCD”), ENTRIES.SVD, LOT.SVD, PSD.SVD, SEARCH.DAT, TRACKS.SVD, plus /MPEG2/ (or legacy /MPEGAV/) sequence tracks, /SEGMENT/ play items, and optional /EXT/ scan or caption files. VCDImager lists “SUPERVCD” as the INFO.SVD system ID for SVCD, XVCD and CVD, and “HQ-VCD” for HQ-VCD. There is no documented CVD-only identifier. Wenzhai Bao’s December 1998 report that CVD and SVCD players used different “disc identifiers” (识别码) to lock each other out suggests proprietary variants existed in practice, but no documentation of those identifiers was found.

Chinese legacy variants documented in VCDImager’s svcd vcd30 build options include the non-compliant /MPEGAV folder (EnReach I-Author) instead of /MPEG2, the deprecated ENTRYSVD signature, and a “chinese /SVCD/TRACKS.SVD format which differs from the format defined in the IEC-62107 specification.” The vcd-info tool also contains a heuristic “CVD interpretation (probably)” when parsing TRACKS.SVD, confirming that real CVD discs were seen with a distinct TRACKS layout.

Programme streams must be packed in 2,324-byte packs aligned to sector boundaries. Every I-frame must be preceded by a GOP header and a sequence header in the same sector, or entry points and scan tables break. SVCD requires scan-information user data in every I-picture so players can fast-forward and rewind; encoders write placeholders and VCDImager fills them with --update-scan-offsets. Official SVCD streams should signal 540 (4:3) or 720 (16:9) in the display horizontal size field; what CVD streams should carry here is undocumented. Peaks above the 2× ceiling cause stutter on real players even when a software compliance check passes.

Subtitles, menus and “protection”

CVD’s subtitles are the one on-disc feature besides resolution that most clearly separates it from IEC SVCD. CVD-style bitmaps travel in MPEG-PS private_stream_1; they are interlaced 2-bit RLE with a four-entry YUV palette plus highlight palette, metadata after the image data, and up to four streams. They are not in IEC 62107. SVCD OGT (Overlay Graphics and Text) uses Philips’ layout with private_data_id 0x70 and sub-stream IDs selecting channels 0-3; VCDImager notes that OGT is “sadly not part of the IEC62107 specs” either, even though it is the Philips SVCD format. VCDImager’s CVD subtitle documentation was reverse-engineered from submux sample code and “a couple of samples of dubious origin,” documenting tags for duration (0x04), coordinates (0x17/0x1f), palettes (0x24-0x27, 0x2c-0x2f), transparency and even/odd row offsets. VLC’s MPEG-PS demuxer is widely understood to map private_stream_1 sub-IDs 0x00-0x03 to CVD subtitles and 0x70-0x73 to SVCD OGT; that mapping was not confirmed from VLC source in the material used here. The 1998 makers marketed “four languages and four on-screen text choices” and “high-definition overlay subtitles.”

Menus inherit SVCD playback control: play lists, selection lists, end lists and (SVCD-only) command lists, with entry points in ENTRIES.SVD acting as chapters. Menu stills are MPEG-2 stills in the segment area at 480×480/576 or high-resolution 704×480/576 under SVCD rules. Makers described this as “two-way interactive playback control” (双向交互式控播); Guangming Daily said SVCD’s VCD 3.0 compatibility gave it an edge in interactivity.

CVD had no documented copy-protection system of its own-no CSS-style encryption, no region code and no Macrovision flag in the standards. The only documented “protection” is the 1998-1999 practice of adding proprietary identifiers and interference codes (干扰数码) so rival makers’ players could not read discs, and the counter-practice of fitting decryption components to players. These were compatibility weapons, not anti-piracy measures. The exact mechanism-modified INFO fields, deliberate errors, or non-standard TRACKS/ENTRIES data-is undocumented.

Further reading on historic video formats

If you want to learn more about historic video formats, get The History of Physical Video Formats from the Frontier by Stephen Driver on Amazon:

• Amazon.de
• Amazon.co.uk
• Amazon.com
• Amazon.ca