[MEncoder-users] Dolby downmix

[Rolf Ernst]

>
> Rolf Ernst <rolf.ernst <at> silverlightning.org> writes:
>
>
>  Now I take the 5.1 6 channel signal and want to downmix to two channel
> surround which preserves at least some of the surround information
>
>  And as I tried to explain in my first mail in this thread I don't think this
> works with MPlayer (I didn't read the sources, but the manual clearly denies it.)
>
>
>  As for the interlacing
>
>  Carl,
>
> I uploaded sample sample_HDPVR_60-24fps_conversion_av_glitch.M2TS. I cut
> around it so ignore start and/or end glitch. At pretty much exactly 15
> seconds into it is a capturing glitch (note they are rare, maybe two or
> three in an hour). You will see that the whole file plays back without a
> hitch using mplayer or windows media player or whatever other
> semi-intelligent player there is. Perfect sync from beginning to end.
>

I use the following command line to convert it to 23.976 fps:

mencoder sample_HDPVR_60-24fps_conversion_av_glitch.M2TS  -o sample.avi -ovc
x264 -x264encopts
threads=0:bframes=5:b-adapt=2:partitions=all:cabac:nopsnr:nossim:deblock:mixed_refs:frameref=6:weight_b:b_pyramid=normal:me=umh:merange=16:subme=6:analyse=all:8x8dct=1:deblock:trellis=1:psy-rd=1,1:no-fast-pskip=1:crf=23
-oac faac -faacopts br=160:mpeg=4:object=1 -vf
tinterlace=4,softskip,harddup,filmdint=io=30:24/fast=0,scale=720:480 -noskip
-mc 0 -fps 60000/1001 -ofps 24000/1001 -demuxer lavf

You can play this back and it has aac audio and it has perfect sync even
across the glitch (this is why I like mencoder so much and believe it is
superior in some ways to ffmpeg).

Now, if you demultiplex the elementary streams and try to remultiplex them
into say a matroska container your video will be out of sync after the
glitch (after 15 seconds abruptly). If you use any other conversion method
than the one outlined in my command line (ignoring, of course, the codec)
you will get jerky video if not immediately then after the flitch. A simple
filmdint will not do. However, this method is rock-solid. I have used it for
dozens of episodes.

If you can show me any way on how to do what I did there, i.e. scale from
60fps progressive down to 24 fps progressive with perfect frame accuracy
across the glitch, keeping perfect a/v sync with ffmpeg and Dolby downmix to
2 channels I would be very interested. With mencoder I discard the channel
info with the above command line and apparently there is no way around it. I
know of no way of how to even reencode the input file (keeping it a 60 fps,
keeping the video stream and only converting the audio stream if necessary)
using any means. The problem is that as soon as I demultiplex the audio and
encode it to aac outside using any given tool I use the timing info and the
mutiplexer has to assume a frame rate (which is not correct right after the
glitch).

Ideas are appreciated.