[MEncoder-users] Demuxing and 6 channel ac3 audio

L Lee llee040 at sbcglobal.net
Mon Mar 9 19:51:54 CET 2009

I'm trying to simplify a process I'm using for transcoding some interlaced
AVCHD files to 24 fps mpeg-2 for saving to DVD video.
(See http://thread.gmane.org/gmane.comp.video.mencoder.user/9689/focus=9790)

I'm using several open source applications to do the job, and I'm relying on
mencoder to accomplish the transcoding of the video. I haven't found it
necessary to modify the audio, so I'm separating audio and video before
encoding. The source audio is 6 channel ac3.

Is there a way to perform the mencoder video encoding step so that the
mencoder output is recognized as a video stream with no audio (a la .m2v) by
mplex so that I don't have to run an additional demuxing operation on it?
I've tried using the -demuxer option as well as specifying the ".m2v" name
extension for the output, but all methods I've used to determine the format
of the results report muxed video even though no audio stream is present.

If not, how can I use mencoder to transcode the original muxed source to
preserve 6 channel audio? So far I've only tried these audio options: -oac
lavc copy and -oav lavc lavcopts abitrate=256 (I've tried 320 and a couple
of other bitrate settings for lavcopts also, including the original 384).
The audio output always contains only 2 channels.

Also, what kinds of extra steps are involved in making standards-compliant
DVD video using 24 fps sources rather than 25 or 30 fps? I always get a
warning about it when using dvdauthor, although I'm able to play the
resulting DVDs with good results using the two means most immediately
available to me, my set top DVD player and computer.

Laine Lee

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