How do I debug why avconv is stalling? - ffmpeg

Question

I'm converting .mov files to .mpg files using avconv. The command being run by my php application is as follows:
avconv -y -i '$finalvideo' -target ntsc-dvd -aspect 4:3 '$mpgvideo' > $logs
I'm able to convert small .mov files to .mpg without any problems. However, I'm unable to convert videos that are over ten or fifteen minutes long. The log file is completely empty. When I run the command directly the frame stops somewhere around 34000 no matter which video I pick.
The cpu shows 97% usage on this process, however, nothing is happening.
OS Ubuntu 10~
How can I gather more information about this stalled process?
Here's the frozen output
avconv version 0.7, Copyright (c) 2000-2011 the Libav developers
built on Nov 3 2011 13:39:09 with gcc 4.3.3
Seems stream 0 codec frame rate differs from container frame rate: 180000.00 (180000/1) -> 23.98 (24000/1001)
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/var/www/sites/default/files/compiled_videos/573-stream.mov':
Metadata:
major_brand : qt
minor_version : 512
compatible_brands: qt
creation_time : 1970-01-01 00:00:00
encoder : Lavf53.0.3
Duration: 00:18:53.49, start: 0.000000, bitrate: 1430 kb/s
Stream #0.0(eng): Video: h264 (Main), yuv420p, 854x480, 1387 kb/s, 25.60 fps, 23.98 tbr, 90k tbn, 180k tbc
Metadata:
creation_time : 1970-01-01 00:00:00
Stream #0.1(eng): Audio: aac, 48000 Hz, stereo, s16, 126 kb/s
Metadata:
creation_time : 1970-01-01 00:00:00
[buffer # 0x9d88820] w:854 h:480 pixfmt:yuv420p
[scale # 0x9d88b60] w:854 h:480 fmt:yuv420p -> w:720 h:480 fmt:yuv420p flags:0x4
Incompatible sample format 's16' for codec 'ac3', auto-selecting format 'flt'
Output #0, dvd, to '/var/www/sites/default/files/compiled_videos/573.mpg':
Metadata:
major_brand : qt
minor_version : 512
compatible_brands: qt
creation_time : 1970-01-01 00:00:00
encoder : Lavf53.10.0
Stream #0.0(eng): Video: mpeg2video, yuv420p, 720x480 [PAR 8:9 DAR 4:3], q=2-31, 6000 kb/s, 90k tbn, 29.97 tbc
Metadata:
creation_time : 1970-01-01 00:00:00
Stream #0.1(eng): Audio: ac3, 48000 Hz, stereo, flt, 448 kb/s
Metadata:
creation_time : 1970-01-01 00:00:00
Stream mapping:
Stream #0.0 -> #0.0 (h264 -> mpeg2video)
Stream #0.1 -> #0.1 (aac -> ac3)
Press ctrl-c to stop encoding
[mpeg2video # 0x9d8bf20] rc buffer underflow
Input stream #0.1 frame changed from rate:48000 fmt:s16 ch:2 to rate:48000 fmt:flt ch:2
frame=33910 fps= 91 q=2.0 size= 151922kB time=336.58 bitrate=3697.7kbits/s dup=5475 drop=530
Oh interesting. I used -loglevel debug -debug. I was seeing this information
stream #0:
keyframe=0
duration=0.000
dts=1133.449 pts=1133.533
size=103
*** 1 dup!
stream #0:
keyframe=0
duration=0.000
dts=1133.449 pts=1133.449
size=104
Until I finally received this message
*** drop!
I have posted my bug with libav
http://bugzilla.libav.org/show_bug.cgi?id=67
thanks for your help.

Answer 1

Try running avconv with a higher log level: -loglevel debug.
That should give you more data. Also, try -dump and -debug.
Are you sure it's not because you're hitting a storage cap?

Answer 2

I ran into this recently with ffmpeg while converting some oddly sized video clips to a "standard" 16:9 x264 & AAC streams inside a mp4 container. When that "Incompatible sample format 's16' for codec 'ac3', auto-selecting format 'flt'" message would show up, my ffmpeg process would frequently just hang indefinitely at 100% CPU use.
I finally found that the issue, at least in my case, was that because of the conversions I was doing (transcoding to an intermediary format then to the final, desired output), it was actually the number of audio stream channels that caused the encode process to hang. By telling ffmpeg to convert the audio stream to 2-channel, I was able to fix this issue permanently.
The same solution will probably apply to avconv. In the ffmpeg world (and because I'm stuck with an outdated version), I merely needed to add -ac 2 to my ffmpeg command and everything worked perfectly!
Hope that helps :)