How to convert .ivr to mp3?

FFmpeg: How can I convert a stream of mp3 bytes to a properly-formatted ogg file?

• I'm using mplayer to dump a m3u stream into an mp3 file, but if I pick up in the middle of the event it doesn't catch the header info on the streamed mp3 file so I just end up with a collection of mp3-formatted bytes. This pseudo-mp3 file plays fine in VLC and Chrome (via <audio>). However, I also need to support Firefox, so I tried converting the file to ogg using ffmpeg; this works, but ffmpeg complains about not finding a header on the mp3 file and in the end Firefox refuses to play the ogg file because it's 'corrupted' (it plays in VLC but without showing a max duration). Any thoughts? (I'm on Arch Linux if it matters.)

• Answer:

  MP3 (per se) doesn't have a header. The MPEG-1 and MPEG-2 video and audio formats were designed to be broadcast to many receivers who might tune in to the channel at any point. As long as you cut on a frame boundary (which you should do!) the result is valid MPEG-1/MPEG-2 audio. If you cut in the middle of a frame, the result will be valid MPEG-1/MPEG-2 audio with a small amount of junk at the beginning before the first synchronization word, which many decoders will still handle fine. But not all. (There are some dubious additions to MP3 designed by warez traders in the mid-1990s, like ID3, that are "file-based" and only come at the beginning. These are not part of the ISO MPEG standards. And Ogg Vorbis is different. Vorbis files usually do contain a header at the beginning of the file that is important to the decoding process.) Cutting MP3 streams on a frame boundary is one way to do it, but this may not be so easy. (In MP3 these generally start with 0xff 0xfa, but not always, and their length can vary if the file was encoded with a variable bitrate.) The easier approach is probably to convert your "cropped" MP3 to a WAV file, and play it back to make sure it sounds good. Then convert the WAV to Ogg Vorbis using the method of your choice.