Originally posted by sytyguy
Directv is coming out with MPEG4 for locals, which is going to be HD in it's finest form, supposedly much better than OTA, which is very, very good...
If one were to accept that statement one would be led to believe that MPEG-4-delivered HD locals from DBS would have better PQ than current MPEG-2-delivered HD. Actually, nothing could be further from the truth, and the opposite will more likely be the case.
In the first place, MPEG-4 H.264 has no inherent PQ advantage over MPEG-2, all else being equal. What's more, there is no way that MPEG-4 could ever be better than or even as good as the original signal it is encoding, and in the case of locals, the signal will begin life (as far as DBS vendors are concerned) as OTA MPEG-2 broadcast in SMPTE310 format. Extracting the bitstream and converting it to a different encoding scheme (MPEG-4) can only increase the total concatenation errors, meaning it might be able to approach the quality of OTA HD, but it can NEVER be actually as good or better.
If they were to decode/decode using the same exact MPEG-2 algorithm, there would be no added concatenation, meaning bottom line that MPEG-2 distribution over DBS has the potential to match OTA HD, while MPEG-4 does not. But that does not mean that MPEG-4 locals will be VISIBLY inferior to MPEG-2 locals on DBS, it WILL be inferior, but not significantly so.
For non-LIL HD on DBS raw video may be encoded directly to MPEG-4, but what determines ORIGINAL encoding quality is the original signal quality and most importantly the profile and level used, which is very similar to the profile and level used for MPEG-2 OTA HD. In that case, the quality level can match MPEG-2, but still never exceed it, all else being equal.
The sole advantage for DBS delivery of MPEG-4 is its coding efficiency, which even if taken advantage of wisely will result in the same PQ, but will allow transmission of more channels and recording of more content within the same hard drive space.
All of this is unimpeachable scientific fact, and not mere opinion.
HD and HD distribution "in its finest form" is HD that is encoded at the recommended profile and level (virtually all is), allowed to maintain proper bitstream levels, and not manipulated by intermediary codecs. A good example is FOX OTA distribution, where the bit rate is about 14.5 Mb/s and the signal remains in pristine ASI format until it is muxed and formatted for SMPTE310 locally, a process that has no losses or added artifacts. The only thing wrong with FOX HD is that they add null packets allowing transitional elements (cuts) to occasionally pixellate a bit, and some of their original content is from 16mm film and looks noisy because of it. Other than that, and when the source material is pristine, OTA HD from FOX is about as good as it gets.