[pvrusb2] Video & Audio out of sync when using mencoder?
rogerx.oss at gmail.com
Sat Nov 19 13:31:34 CST 2011
> On Sat, Nov 19, 2011 at 11:28:20AM -0600, Mike Isely wrote:
>Audio and video are muxed together by the capture device itself not by
>anything about the host. There's basically NOTHING that any outside
>software can do to interfere with that process.
>Now, with that said, it's possible that the de-muxing might get screwed
>up. If you're using mencoder to "record" I presume you're doing this in
>order to transcode the stream to a different format, right? That means
>that mencoder is going to de-mux the incoming stream and re-mux the
>re-encoded results to your desired output format.
>I have seen cases where mplayer will lose audio / video sync because
>it's not getting the incoming stream data at a consistent rate - which
>can happen if the capture device is having reception problems. A
>drop-dead absolute method to determine if this is the case is to instead
>of running mplayer directly on the stream that you instead cat the
>device's output to file and THEN run mplayer on the file. If you do
>this and all sync issues go away then it's mplayer doing something
>strange - because when you're feeding it a ready-made file rather than a
>live stream then there are no gaps / breaks.
>Now you said you're using mencoder not mplayer. However they share the
>same codebase and if mencoder is really de-muxing / re-muxing the stream
>then I could see a similar problem happening. Try sending the capture
>device output to a file for 5-10 minutes, then run that file through
>mencoder and see if you're still having sync issues.
>The last paragraph at the following URL talks about audio/video sync
>issues with mplayer:
Yea. I grepped all that early this morning. :-/
However, you did mention the hvr-1950 device already feeds mencoder (or
mplayer, or whatever application) an already completely muxed stream.
Which did spark an idea as to then, "Why am I using the following incantation
mencoder 'dvb://KTVF DT:545028615:8VSB:65:68:4' -really-quiet -of avi \
-ovc copy -oac copy -o /stored/tv/blah.mpg
I thought I was already merrily copying the stream as is (to save CPU cycles)?
Should I use a different incantation?
Also, analog TV is pretty much gone here, if not totally gone. So using cat
/dev/video0 without an analog signal isn't really possible unless I feed
something through the composite port. Is there a way to simply 'cat' the DVB
side? (I thought I was using 'cat' at one time on the DVB side somehow?)
Anyways, I tried one of my old 2.6 kernels, a year old mplayer/mencoder version
and nothing is in sync yet. I'm starting to wonder if it is bad reception too
at this point. As sometimes stuff is in sync, then all of a sudden video
unnoticibly slows, while audio advances.
I'll probably start Googling in another hour or so on the data I now have.
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