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SVCD Digital Video

With over 20 million households owning VCD payers by the late 1990s, it is unsurprising that China was instrumental in the development of a successor to the VCD format. The first of three independent efforts to bring the next-generation VCD standard to the Chinese market started in 1997. C-Cube Microsystems – the market leader manufacturer of VCD systems – was first to market with its CVD (China Video Disc) product a year later. However, thanks to the intervention of the Chinese government it was the “SVCD” standard developed by a consortium that included Philips, Sony, Matsushita and JVC – the companies that created the original White Book VideoCD specification – that was to eventually win out.

The 1998 “Super VCD” (from the Chinese “Chaoji VCD”) format – subsequently standardised as ISO IEC 62107 – is a natural evolution of the VCD standard. The basic difference is that MPEG-2 is used for the video stream (instead of MPEG-1), which is encoded at higher resolutions and bitrates. It also allows subtitles and variable bitrates. As a consequence, SVCD is capable of delivering up to 2 times sharper video images than its predecessor, at the cost of reduced capacity – typically between 35 minutes and 80 minutes depending on the average bit rate used – per CD. Most feature length movies, therefore, are distributed on a 2- or 3-CD set.

In common with VCD, SVCD supports 16:9 (anamorphic wide screen) image aspect ratio. However, unlike its predecessor, some SVCD players can signal the TV set to automatically switch to the appropriate mode. The format has extensive support for subtitling and karaoke lyrics colour highlighting, neither of which were possible in VCD 2.0. An SVCD video stream can contain up to four independent subtitling channels for different languages. The subtitles are overlaid on the top of the video image in real time, and may be enabled or disabled at will. Since the subtitles are stored as bitmap graphics, they are not tied to any particular character set. Finally, the SVCD standard supports HTML style hyperlinks, still images, playlists/slideshows, multi-level hierarchical menus and chapters (indexing).

The table below summarises SVCD’s principal technical characteristics:

Features SVCD 1.0
Video

bit rate

NTSC resolution

PAL resolution

 MPEG-2

variable up to 2.6 Mbit/s

480×480 interlaced, 29.97Hz

480×576 interlaced, 25Hz
Still picture (photo)

NTSC resolution

PAL resolution

 MPEG-2 I Frame)

480×480, 704×480

480×576, 704×576
Audio

sampling

bit rate

audio channels

surround sound

 MPEG-1 layer II

44.1kHz

from 32 to 384Kbit/s

up to 2 stereo or 4 mono

MPEG-2 (5+1) extension

Since commercially produced SVCD titles only be available in Far East, it is unlikely that standalone SVCD players will become available outside of China and surrounding countries. They are generally compatible with VCD 1.1, VCD 2.0, CD-i and CD-DA formats and some are capable of playing MP3-based CD-ROMs. Whilst SVCD players can’t play DVDs, the fact that they both use the same MPEG-2 encoding scheme means that some models can be “upgraded” to handle the format simply by replacing the CD drive mechanism with a DVD drive.

Until late 1999 it was only DVD players sold in Asia that were capable of playing SVCDs. Nowadays this shouldn’t be a problem. If it is, especially since DVD players are based on only a small number of underlying platforms, it will often be possible to get a player to handle the format by means of a firmware hack.

XVCD and XSVCD – eXtended VCD and eXtended SVCD respectively – are unofficial “tweaks” of the VCD and SVCD standards designed to achieve improved image quality, for example by increasing the bit rate in line with modern CD-ROM drives’ faster data transfer capability. XSVCD works on the principal that since DVD players can handle SVCD media and the MPEG-2 encoding scheme is common to both SVCD and DVD, it ought to be possible to push the SVCD format a little further towards DVD levels of performance. Consequently, it increases bitrate limits up to the same level as DVD-Video – up to 9.8Mbit/s – and supports use of full DVD resolutions in addition to SVCD’s regular 480×576/480×480 resolutions.

Since neither XVCD or XSVCD formats are official standards there are no guarantees as to whether they will be handled by available standalone playing devices. In practice, whilst most major brand players won’t play them, many players manufactured in the far east will.

 

Filed Under: Digital Video

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