On Tue, 08 Mar 2011 00:38:51 +0000, Meat Plow wrote:
On Mon, 07 Mar 2011 16:31:32 -0800, Jeff Liebermann wrote:
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/...orner-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. Ive 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/...presto-change-
o.aspx
Bookmarked for perusal tomorrow morning after coffee.
All a very good read. I've been around digital video since 1998. I've
worked with encoding/transcoding/etc.. for a decade. Current streaming
of popularity seems to be done in a TS (transport stream) container.
In order to get to that TS container obviously the raw video has to go
through several processes. Obviously there are not enough checks in place
to ensure the video and audio are sync'd.
--
Live Fast, Die Young and Leave a Pretty Corpse