[mythtv-users] nuvexport ffmpeg video quality

Joel Ebel mythtv at ebel.mybox.org
Wed May 11 07:20:27 UTC 2011

I'm happy to see the 6-channel audio problem resolved with mythexport. 
now nuvexport is usable.  However, I'm still running into video quality 
issues and looking for advice.

In my previous mythtv install, I used nuvexport with transcode and Xvid. 
  I used single pass with a quantizer value of 4.  I don't particularly 
care about exact bitrates or file sizes.  I just want consistent decent 
quality and a fast encode.  Using single pass seemed appropriate and 
worked well before.

Now, with the 24-fixes branch, transcode support is removed, so it's 
either ffmpeg or mencoder.  With ffmpeg, I get larger files and much 
worse quality using the same settings I previously used with transcode. 
  The output is very blocky.  I can get better results by using 
multi-pass encoding, though still not as good as what I got with 
transcode. Dropping to quantizer 3 makes very little improvement. 
Multi-pass encoding definitely takes longer, and seems unnecessary when 
I don't care about exact bitrates.

I tried mencoder and got much better results, however, the encode went 
much slower, and the total frame count was incorrect, so the progress 
meter was incorrect.  My first guess is it counted frames from the show 
before the cutlist was applied.

So what settings are people using with nuvexport?  Am I in the minority 
for not using multipass, so it isn't a tested code path?  What settings 
do people typically use that give a good balance of compression, 
quality, and encoding speed?


For reference, these are the ffmpeg and mencoder commands that nuvexport 

ffmpeg -threads 4 -y -f s16le -ar 48000 -ac 2 -i 
/tmp/fifodir_20851/audout -f rawvideo -pix_fmt yuv420p -s 1280x720 
-aspect 1.77777777777778 -r 59.940 -i /tmp/fifodir_20851/vidout -aspect 
1.77777777777778 -r 59.940 -s 624x352 -vcodec libxvid -b 1024k -minrate 
32k -maxrate 2048k -bt 32k -bufsize 65535 -flags +mv4+loop+aic+cgop 
-trellis 1 -mbd 1 -cmp 2 -subcmp 2 -b_qfactor 150 -b_qoffset 100 -bf 1 
-qmax 31 -qmin 4 -acodec libmp3lame -async 1 -ab 128k -f avi 
/mnt/storage/videos/The Simpsons - The Devil Wears Nada.avi

mencoder -aspect 1.77777777777778 -noskip -idx /tmp/fifodir_13604/vidout 
-audiofile /tmp/fifodir_13604/audout -demuxer 20 -audio-demuxer 20 
-rawaudio rate=48000:channels=2 -demuxer 26 -rawvideo 
w=1280:h=720:fps=59.940 -ovc xvid -oac mp3lame -lameopts vbr=3:br=128 
-xvidencopts fixed_quant=4 -o /mnt/storage/videos/The Simpsons - Pranks 
and Greens.avi -vf scale=624:352

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