[FFmpeg-user] What does 'i[0][0][0] 0x0069' after mp3 codec mean?

Weiwu Zhang zhangweiwu at realss.com
Sun Jan 19 13:22:37 CET 2014

2014/1/19 Zhang Weiwu <zhangweiwu at realss.com>:
> Newbie. Using ffmpeg 1.2.4. Plenty of googling before asking in the list.
> Sometimes the codec mp3 is followed by
> U[0][0][0] 0x0055
> And sometimes:
> i[0][0][0] 0x0069
> What does that mean? I am guessing the U/i is an indicator whether or not
> the mp3 stereo is joint-stereo, but 0055 and 0069 is beyond me.

After more study of mp3 joint stereo, it turns out there are 3
possible coding of stereo mp3:

1. Joint-stereo, Intensity stereo coding
2. Joint-stereo, M/S stereo coding
3. Not joint-stereo. Each channel is encoded seperately.

If you count mono in, there is a forth mode: no stereo.

A post, I found by googling, said 99.99% mp3 stereo are encoded in
Join-stereo. So, perhaps

i[0][0][0] 0x0069

menas "intensive stereo"


U[0][0][0] 0x0055

should mean "M/S stereo". Unless I happen to own a 0.01% mp3 that
really uses two seperate channels for left and and right, in which
case "U" means "Unique" for dual unique channels.

My guess so far. Perhaps totally wrong, but I prooved that I worked
hard trying to help myself before asking everyone.

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