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Discussion Starter · #1 ·
Over the years, I have seen/heard a lot of problem with AC3/DD5.1 audio not coming through consistently on all channels. Sometimes people will report that one network affiliate will have it, another maybe DD but missing the subwoofer, or no DD5.1 at all.


My question is - how do the professional MPEG2 encoders deal with the audio path? Are the MPEG2 encoders all video only, and the audio has to be done through separate Dolby Digital encoders then muxed back in with the video stream?


I envision that a progam starts somewhere and hops through a whole bunch of encoders on its' way to your HDTV set. At each of the hops is some spaghetti of wires where the AC3 is decoded, turned to 6 analog audio wires, then fed to another encoder. Is this correct, or are there some encoders that are digitally passing through the audio stream without having to decode it in-between.


I know that the HDTV streams are often re-encoded many times because the video datarate starts out high, and then have to drop down through many steps as the data path gets slower and slower as it gets ready to finally be sent in

All of this probably relates to lipsync problems as well. We used to see reports of that as a widespread HDTV problem, but it seems like the broadcasters are getting much better at avoiding that.
 
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