Video compression technologies are a much talked about theme in the broadcast industry and for good reason. Once quality is lost, it’s gone for good. As a company with a long heritage in digital TV we know as well as anyone that MPEG, the reigning champion, has played a crucial role in enabling digital TV to move from interesting idea to profitable consumer service. Although we believe MPEG will continue to play a central role in digital TV, we believe that for high quality video contribution, JPEG2000 is the clear winner.
MPEG was originally intended to distribute digital TV to set-top boxes in the home. MPEG is bandwidth optimized and designed to facilitate low cost consumer devices.
MPEG and JPEG2000 are fundamentally different. MPEG compression is built around a group of pictures structure. MPEG compression works by only sending partial information, this increases the risk of errors that then affect the whole group of pictures. The MPEG encoding mechanism can cause a substantial delay, which results in undesirable time differences across different delivery media. JPEG2000 on the other hand encodes each picture individually and therefore any errors are less visible so as to be almost undetectable. The JPEG2000 encoding scheme results in considerably less delay than MPEG – less than 120 msec. MPEG encoding is based on macroblocks. The result of an error in an MPEG video stream often produces a blocking effect in the picture over several frames. Errors in a JPEG2000 stream create less visual artifacts than MPEG-based solutions, as the errors appear as a one frame blur in the picture. This is much less visually disturbing than the blocking effects of MPEG.
This makes JPEG2000 ideally suited for the more demanding video transport arenas such as live sports events.
Video quality - JPEG2000 includes a tool set for high-quality video, with support for 10-bit video. Whereas the driving force for MPEG-4 has been to deliver a good video quality at low bitrates e.g. for TV over DSL lines, JPEG2000 has been defined to produce high quality compression of single pictures. This requirement fits well with really high video quality applications such as Digital Cinema and live broadcast contribution.
Multiple compressions - One of the challenges of using MPEG compression for contribution purposes is that the picture quality degrades at every compression step. JPEG2000 compression technology works in such a way that even with multiple compression steps video quality remains high.
Last mile efficiency - JPEG2000 when used in the contribution stage improves the quality of the direct-to-home broadcast by improving the television source signal entering the distribution encoder. Experience shows the last mile MPEG-4 bitrate can be reduced by 15% while maintaining the same video quality.