MP42Foundation comes up with a different bitrate than iTunes for M4A files

[Andrew Hyatt]

Upon using MP42Foundation to modify metadata and add artwork to M4A files (all 256 kbps and from iTunes) and calling update on the MP42File, the bitrate displayed for the files in iTunes changes.

I am not aware of any implications other than the displayed bitrate being different.

Why is MP42Foundation recalculating the bitrate when only the metadata was modified?

The bitrates change from 256 kpbs to anywhere from 258 to 282 kpbs. Since none resulted in a lesser displayed bitrate, maybe the added artwork and metadata is causing a greater bitrate to be calculated?

[Damiano Galassi]

iTunes doesn't write the real track bitrate (probable because people don't understand that constant bit rate is not possible with modern codecs). MP42Foundation always recalculate each AAC track bitrate, if you don't want this behaviour you have to pass MP4_CLOSE_DO_NOT_COMPUTE_BITRATE to the MP42Close() call.

[Andrew Hyatt]

Thanks, submitted a PR with this option