#584 CBR AAC Files incorrectly listed as variable

[Fred]

Using the newest version of MediaInfo x64, with the newest version of Nero's AAC encoder, CBR AAC files are incorrectly listed as variable. The correct bitrate is detected, although an incorrect "maximum" bitrate is detected, generally ~16kbps higher than the actual CBR bitrate. The encoder settings detected, however, look correct, with a constant bitrate and the correct flag for LC/HE.

[Jerome Martinez]

IMHO this is a bit difficult to detect "CBR" AAC because AAC frames are not same size exactly in "CBR" mode.

I can try to create an algo detecting "nearly" CBR frames and display the stream as CBR.

Please provide a sample file.

[Fred]

Picture of output

[Fred]

I've had a discussion on a forum about this, apparently it's because AAC doesn't actually use a proper CBR algorithm, it's merely a very constrained ABR algorithm. Your best bet would be to read the encoder settings first, and if the -cbr setting is detected, simply override the results to be "constant" with a bitrate of the detected encoder setting/1000 (since it's in bps).

For some reason it wouldn't allow me to directly upload an MP3 (probably
too large of a file or a network timeout), so here's a link. I've also
uploaded a picture of the output and highlighted the correct/incorrect
bits.
http://fileape.com/dl/98CVW4vptFku8A54