[mythtv-users] Audio lags when transcoding 720p from cable box firewire

Ken Scales kscales at xplornet.com
Tue Mar 3 03:04:38 UTC 2009


Stephen Sassman wrote:
> I have been trying to transcode some 720p video captured from the
> firewire of my cable box (motorolla 6200 series). I am transcoding to
> x264 to a matroska container which works perfectly with my ivtv
> recordings. The problem that I am having is that the audio track lags
> behind the video, and it gets worse as the video progresses. By the end
> of a 90min movie, the audio can end up more than 10 sec behind the
> video. I have tried using avidemux, mencoder, and ffmpeg with the same
> result. Here is the command line that I'm using in mencoder:
>
> mencoder file.mpg -vf crop=944:688:168:16 -ovc x264 -x264encopts
> subq=6:me=umh:8x8dct:partitions=all:bframes=3:frameref=3:mixed_refs:dct_decimate:threads=0:weight_b:crf=23
> -oac copy -o file.mkv
>
>
> I use similar settings with ffmpeg and avidemux. The original mpeg has
> no issues with audio sync. I have seen mention of similar problems, but
> never a clear solution. Any idea?
>   

I've had similar "sliding" sync problems transcoding 720p recordings 
captured with my Hauppauge HD-PVR with mencoder/ffmpeg.

I've been using Handbrake (http://handbrake.fr) for a couple of weeks, 
and have been having pretty good results so far.  I've created a custom 
preset for my transcodes (MPEG-4, AC-3 copy, into a mkv container).  
Handbrake will use multiple threads, and tends to run around 235% to 
240% cpu on my C2Quad (vs mencoder at 135-170%). This is on Ubuntu 8.10.

I've had a couple of recordings with 70 and 110 msec audio delays, but 
it seems constant through the recording, so can be dealt with fairly simply.

Might be worth a try for you too.
/Ken



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