Audio Bitrate always comes out wrong
I'm a commercial editor at a TV station. We occasionally have to load completed videos to a service/site called Premion for putting local ads onto streaming services such as Hulu. The problem is that Premion is EXTREMELY picky and will not accept anything even the slightest bit outside of their recommended specs. Those specs are H.264 QuickTime format, with .mp4 file type, 10-50 mbps video bitrate, audio that's AAC, 48kHz, 192 or 256 kbps. That last one is the main problem.
The program that we were originally given to convert videos that were originally made for broadcasting to Premion specs wasn't outputting the specs quite right, so I taught the people who handle this daily how to download and use MPEG Streamclip, since its free. They still had to come to me once every few days to fix things that it couldn't quite get right (video missing two frames and now Premion considers it to be 14 seconds instead of 15, etc.). Often the audio bitrate would also be wrong.
Today we had a doozy of an ad that absolutely refuses to conform to the recommended specs, particularly with the audio bitrate, which is supposed to be 256 kbps (192 is also acceptable, but we've had similar results trying that). Avid Media Encoder with precedence set to Bitrate in Advanced audio settings comes out to 254. iSkysoft Video Converter (Mac) is usually my champ, but it gives me 191 kbps no matter what I do. QuickTime Pro (PC) doesn't get very close at all. VLC Media Player's export isn't even playable for some reason. The closest anything has gotten has been MPEG Streamclip for Mac, which gets it right according to its own analysis, but according to the "Details" tab of Properties when I move the file to a PC, is just barely off at 255.
What do I do? Why is the audio bitrate always coming out wrong?
Also, this is an ad that we originally edited but didn't shoot ourselves, so I can toy with a few more things.
I may be wrong about this....but I thought AAC was, by nature, a Variable Bit Rate compression format. So AME allows you to set "precedence" meaning you want to force it, as much as possible to conform to either "Bitrate" or "Sample Rate"...but even within the precedence their is still allowance for it to slide as needed.
I'm not sure a great way around this other than your previously described work arounds for trying to get a file to conform. It may help to run the file through as an completely different format (Quicktime file with PCM audio) and then convert that back to h.264 with AAC audio and see if it forces it into the mold?