Originally Posted by Kipp Jones
I disagree. If the original content was transmitted in MPEG2, then uncompressed and then recompressed to MPEG2 via 1394, no bit loss, the original content would be intact and therefore equal to HDMI.
Also, if a device simply had a 1394 output skipping the HDMI output, the PQ would be the same. The difference is where the uncompressing is done.
For the record, 1394 is now at 3.2Gbps over fiber as demonstrated at CEDIA 2006.
They now have enough bandwidth to transmit HDTV including 1080p uncompressed if they wanted to. Recording HDTV on top of that is a bonus.
MPEG2 (and all the other codecs like MPEG4, H264, VC1, etc) is a lossy compression. Each time it is compressed, information is lost (like an mp3). Thus, if the original MPEG2 content is uncompressed, then re-compressed one more time (i.e. more information is now lost), the quality of the 2nd compression will certainly be lower. It's similar to taking an mp3, decompressing to wav, then re-compressing into an mp3 again. The 2nd version will be lower quality than the first.
The only equivalent "lossless" way would be to never decompress the original MPEG2 content (say from the disc or off the air), transmit it over 1394, then get decompressed at the display. But you still have the problem of not being sure whether the TV has the right decompression codec.