Convert flash videos (flv) to mp4 for viewing on your ipod.

ffmpeg -i FILE_NAME.flv -ar 22050 NEW_FILE_NAME.mp4

The -ar 22050 is the sample rate and it makes a big difference with audio quality. It is usually necessary to set a sample rate when encoding flv files because the MP3 encoder only supports rates of 11025, 22050, and 44100 Hz.

For practical uses you will probably want to take control over more of the quality settings for something that looks like:

ffmpeg -i video.mov -b 600k -r 24 -ar 22050 -ab 96k video.flv

These are the common settings and an explanation of what they do:

• “-b 600k” selects a video bitrate of 600 kilobits per second. This is a compromise between quality and bandwidth (with older versions of FFmpeg you would use “-b 600”. Type “ffmpeg -h” to check which units are expected in your version);
• “-r 24” selects 24 video frames per second;
• “-ar 22050” selects an audio sample rate of 22050 Hz, which is sufficient for voice;
• “-ab 96k” selects an audio bit rate of 96 kilobits per second; you could go a little lower for voice-only audio (with older versions of FFmpeg you would use “-ab 96”. Type “ffmpeg -h” to check.)

ffmpeg can also be used to convert to avi, wmv, mpg, and mov i believe.

More info found here and here where all of this info comes from.