There are significant differences between MPEG-4 and JPEG 2000 for broadcast contribution. (See Table 1.) Further development of video and still image compression standards continues, and there will no doubt be future advancements for both standards. For example, High Efficiency Video Coding (HEVC), unofficially called H.265, promises improved video quality and data compression, as well as support for higher resolutions.
Broadcast contribution links seek to have the highest video quality because the signal may have to go through post-production editing. The output video quality from the contribution stage is propagated to the distribution link. As a consequence, the quality and efficiency from the distribution link is highly dependent upon the level of quality experienced during contribution. Broadcast contribution signals should be lightly compressed — almost equal to the original uncompressed signal — so there is minimal quality loss under multiple generations of encoding.
JPEG 2000 can compress HD video to a significantly lower bit rate, and then extract the video with no loss of information. When peak signal to noise ratio (PSNR) performance is used to compare original footage with video compressed with JPEG 2000, the degradation is close to visually lossless and deviation from the original is low. The PSNR of footage encoded with MPEG, however, can vary greatly from picture to picture due to different methods of prediction.
Recently, the performance of JPEG 2000 and MPEG-4/AVC under multigeneration encoding was evaluated using a single vendor’s encoders and decoders. (See Figure 3.) Video quality was measured in terms of PSNR for different HD interlaced sequences at the operating points of the encoders. The streams were encoded at 90Mb/s for JPEG 2000 and 45Mb/s for MPEG-4/AVC streams. These bit rates were used throughout the testing because they are common operating points.
MPEG-4/AVC provided high-quality video at 45Mb/s. Under multigeneration encoding and decoding, the PSNR reduction was sharp — roughly 2.2dB after the fourth generation. (See Figure 4.) JPEG 2000 also delivered high-quality video (at 90Mb/s), but it had less than 0.5dB loss after the fourth generation of encoding and decoding, which was less than one quarter of the reduction experienced by MPEG-4. In addition, the predictive coding of MPEG resulted in an end-to-end latency of approximately 1 second, which is roughly 10 times more than the latency experienced with JPEG 2000.
For another round of tests, designed to evaluate the influence of contribution encoding on end-user quality, a distribution encoder was used to encode the incoming signal using 4:2:0 8-bit at 6Mb/s, 8Mb/s and 10Mb/s (common settings for IPTV applications). The tests showed that because of JPEG 2000’s high video quality, it is possible to increase the compression ratio for the final compression to broadcast without quality loss, saving from 5 percent to 15 percent of the total bit rate, depending on the final bit rate used for distribution. By spending more money on contribution, it is possible to save on broadcasting to the home, because more content can be placed in the available bandwidth.
To illustrate the bandwidth savings that can be achieved when employing JPEG 2000 video compression, consider an uncompressed HD-SDI signal, which has a bit rate of about 1.5Gb/s. (See Table 2.) A JPEG 2000 encoder/decoder can maintain the quality of the original signal with a bit stream of 500Mb/s to 800Mb/s, depending on the content. At 600Mb/s, virtually any type of high-quality HD content will be transported mathematically losslessly with a JPEG 2000 system. Reducing the bit rate from there will increase the possibility of mathematical image loss, but any errors will be visually imperceptible even at far lower bit rates.