CBR issue

Hello felmakoudi,

This is a great topic to bring up! You're not doing anything wrong here at all. In fact, the issue here is with the way mediainfo calculates AAC audio with frame size.

AAC uses the concept of a bit reservoir, which allows it to spend more bits on the demanding parts of the audio signal and then save bits for the easier (less complex) parts, while at the same time allowing the transport over constant rate channels by buffering the bit reservoir. This mode is called CBR mode. Therefore, the bitrate of audio does fluctuate even in CBR mode.

In addition, mediainfo reports the audio as VBR due to how MediaInfo extracts the metadata of the files output from MediaConvert. Essentially, it is being reported by mediainfo as VBR; however, if you have chosen "CBR" for both the audio and video, the output itself should be fine. MediaConvert AAC output is considered CBR by AAC specification.

I hope that explanation helps!

Kind regards,
Jeff

Thank you very much for the explanation