On Mon, 7 Mar 2011 19:57:03 +0000 (UTC), Meat Plow
wrote:

On Mon, 07 Mar 2011 10:48:00 -0800, William Sommerwerck wrote:

Can anybody comment on lip sync?

On Comcast a few channels have imperfect lip sync. As to why -- I don't
know.

I've only had a small problem with Discovery HD. Once in a while I get
some pixelation. Something you would expect with a less than adequate
signal. But that's not the case. And the cable company can't explain it.

This might add fuel to the fire. Note that this is from a cable
industry insider, published in a CATV industry journal:

http://www.cedmagazine.com/articles/2011/02/ciciora-corner-can-you-hear-me.aspx
Digital television has brought the scourge of “lip sync” errors.
Video signals and aural signals require vastly different
processing, which results in different amounts of processing time.
Unless appropriate additional artificial delay is added, the sound
and the video will end up out of synchronization. This difference
can accumulate if multiple conversions take place in the path from
the original source to the final display site. I’ve seen lip sync
discrepancies that were so bad, it appeared that the characters
were speaking another language and that the speech I was hearing
was dubbed in. The problem is so pervasive that my sound system
comes with a delay adjustment so that I can manually compensate at
home. That would be a reasonable solution if the delay was
constant from channel to channel, or even from program to program
on the same channel. But it is not.

On the home front, I've seen sound sync fall apart when ripping and
transcoding content from a DVD to some other video protocol. There
are tweaks for the problem, such as VLC which allows you to speed up
or slow down the audio using the "f" and "g" keys. You can also
"desync" the video and audio for a fixed user settable delay. The
problem is that controlling the sync seems to be too much of challenge
for broadcasters and cable companies. To make things worse, it seems
(to me) that different ATSC decoders have varying delays. It's
suppose to be controlled to between +15 and -45 msec but I'm beginning
to have my doubts:
http://www.pixelinstruments.tv/articles.htm
http://www.pixelinstruments.tv/articles5.htm
(Lots more on audio sync on the above URL).

Incidentally, if you also happen to notice that cable video doth suck,
you might find this article, from the same issue, rather illuminating:
http://www.cedmagazine.com/articles/2011/02/transcoding-presto-change-o.aspx

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