We’re using ffmpeg to encode videos for flash on several of the sites I’m involved with, and this usually works flawless. From time to time there’s however certain video files that makes something go wrong, usually small issues like stuttering at random places. Today I decided to go bug hunting and try to find out exactly what triggered this behaviour in one of our recent videos.
After quite a bit of debugging and re-encoding the offending video segment (which limits the rate of debug attempts, as you have to wait a couple of minutes ++ for each encode), I decided to try to simply use -acodec copy for the audio codec. The Quicktime file already used AAC as its codec, and the file we were encoding also used AAC. The stuttering disappeared! This indicates that the sound encoding of the process were to blame for the stuttering, so if you’re having a sound related problem, try to copy the input codec to the output source.
As libfaac and libfaad were the two only involved libraries of the encoding and decoding process, the first thing to try were to check if there were any new versions of these libraries available. And lo’ and behold, both libfaac and libfaad had been updated since the versions included in our ubuntu version (no real shocker there, as things in the audio and video codec world moves with a rather high velocity).
I removed the packages (sudo apt-get remove libfaac-dev libfaad-dev) from Ubuntu, downloaded the new libfaac and libfaad versions, compiled (./configure && make) and installed them (sudo make install), and then recompiled ffmpeg with the new libraries in place. ffmpeg then complained about libfaac.so.2 missing, but a quick run of ldconfig (sudo ldconfig) fixed that issue.
Re-encoding the file yet again – and wooho! The offending file now works as it should. This probably also solve the issue we’ve been seeing for several other files too. The new versions of libfaac and libfaad solved the issues we were having.
BTW: There’s a small fix needed to make libfaac compile with gcc4.