[FFmpeg-user] [Bulk] Re: ProRes Quicktimes with audio not playing back reliably

[Tim Nicholson]

On 24/09/12 08:30, Tim Nicholson wrote:
> On 23/09/12 04:43, Bob Maple wrote:
>>> Does it work if you use another audio codec?
>>> (aac with high bitrate)
>>
>> Ah - forgot to finish testing that the other night as well (I was
>> getting errors about AAC being 'experimental' and then got sidetracked
>> on something else.)
>>
>> But no, AAC doesn't work, nor does MP3.. still get glitchy
>> playback/dropped frames.
>>
>> For fun I also tried still using PCM and changing the bit depth and
>> sample rate to no avail;  pcm_s24le at 48khz is still not good,
>> pcm_s16le at 44.1khz is still not good, etc.
>>
>> Back on the video front, I tried MJPEG as suggested by Thomas which
>> works fine, and I also just did DNxHD and it plays fine as well.  So it
>> seems to be something with Prores specifically.
>>
> 
> 
> I can confirm that on playing back some recent ProRes files in QT player
> 7 I was seeing random picture freezing/jumping with audio playing
> smoothly, which, if you stopped and went back over the same material did
> not occur/occurred in a different place. I was putting this down to
> pulling the files over the network until I saw this thread....
> 
> My coding parameters were:-
> 
> ffmpeg version N-44123-g5d55830
> -c:v prores -profile:v 3 \
> -c:a copy \
> (Audio was 4 streams of pcm_s24be)
> 
>>
>> |  Bob Maple
>> [..]
> 
> 

OK I've done some more investigation on this.

Copied a sample file locally, and it still exhibits the issue.

Created a test file with the same coding parameters as was used by the
sample file as above using the following command line:-

ffmpeg -f lavfi -i "testsrc=duration=600.0:size=720x576:rate=25" \
-f lavfi -i "aevalsrc=0::d=600.0" -f lavfi -i "aevalsrc=0::d=600.0" \
-f lavfi -i "aevalsrc=0::d=600.0" -f lavfi -i "aevalsrc=0::d=600.0" -map
0:v -map 1:a -map 2:a -map 3:a -map 4:a \
-vf "drawtext=fontfile=/usr/share/fonts/truetype/DroidSans.ttf: \
timecode='00\:00\:00\:00': r=25: x=(w-tw)/2: y=(1*lh): \
fontcolor=white: fontsize=60: box=1: boxcolor=0x00000000 at 1" \
-c:v prores -profile:v 3 \
-c:a pcm_s24be -ar 48000 \
-y Prores_test_A.mov

This file does not show any of the problems (as evidenced by QTPlayer
<apple I> info box showing the rate stuttering or any visible stutter of
the timecode, or scrolling rainbow).

I note that my original file, duration 11 mins 03 secs is 4.8G in size,
and the lavfi version, duration 10 mins is only 1.7G. A recoded version
of the original to the same codec and level (done in QT Pro) is just
over 5G (but the audios have been merged into a 4 channel stream from
the 4 discrete streams). This has no issues.

I therefore wonder if the problem is buffer related, with the more
complex material coded by ffmpeg exceeding a limit momentarily, with the
Apple coded material being within the limits, and simple material coded
by ffmeg just fortuitously staying within limits.

-- 
Tim