Re: [mad-dev] max mp3 frame size?

Andre wrote:

...

According to "Bertrand Petit" who wrote madlld (mad low-level demonstration): (can found in MAD main page)

• When this occurs, the remaining unused bytes must be
• put back at the beginning of the buffer and taken in
• account before refilling the buffer. This means that
• the input buffer must be large enough to hold a whole
• frame at the highest observable bit-rate (currently 448
• kb/s). XXX=XXX Is 2016 bytes the size of the largest
• frame? (448000*(1152/32000))/8

I'm not sure where 448 kb/sec comes from.... ?

448 kbps is the highest possible bitrate for MPEG audio, but it is only possible for Layer I. Since there are only 384 samples per frame in Layer I, the above formula doesn't calculate the correct frame size.

If you substitute 320 kb/sec into the above formula however, the largest possible MP3 frame comes out as 1440 bytes which I believe is the correct answer.

This is correct for MPEG-1 and MPEG 2.5 Layer III. In theory frames at 320 kbps could have their padding slot bit set for a total of 1441 bytes.

-rob