Convert Mpeg to 3GP file
Now I expected this to be hard. Or at least take a lot of fiddling to get right. However, it seems to be quite easy. http://www.niemueller.de/wiki/index.php?[[ConvertVideoTo3GP|This]] site has all the goodness. It requires three steps. Now assume we have a file called movie.mpeg and we want to convert it to movie.3GP. The steps required would be
mencoder movie.mpeg -nosound -ovc lavc \ -lavcopts vcodec=mpeg4 \ -vop expand=176:144,scale=176:-2 \ -o movie.avi -ofps 12
This will extract the video, scale it and reduce the frame rate. Now we need to extract the sound.
mplayer -vo null -ao pcm -af \ resample=8000,volume=+4db:sc movie.mpeg
An output file called audiodump.wav will be created that has the audio that we require. Finally we need to combine these two files together.
ffmpeg -i movie.avi -i audiodump.wav \ -b 48 -ac 1 -ab 12 -map 0.0 -map 1.0 movie.3GP
And that is that. Next I need to bundle this lot up into a script so I can then forget all about how this works.