I discovered that the mp4 files I was writing were viewable in VLC and in
Chrome-on-desktop (ffmpeg-based) but not in Chrome-on-Android
(libstagefright-based). It turns out that I was writing Annex B sample data
rather than the correct AVCParameterSample format. ffmpeg gives both the
"extradata" and the actual frames in Annex B format when reading from rtsp.
This is still my simple, unoptimized implementation of the Annex B parser. My
Raspberry Pi 2 is still able to record my six streams using about 30% of 1
core, so it will do for the moment at least.
This code isn't pretty exactly---particularly the hardcoded lengths---but it
does work. I'll have a different mechanism for calculating the length and
nesting structure forthe more dynamic parts of the moov atom. This way is
convenient when generating a single string of mostly static data.
