Distinguishing the actual Bit Rate of an audio file

The bitrate of the auto is the storage potential for the data that makes up the frequencies and amplitudes of an audio file Different codecs allow for better compression, deletion of frequencies that won't be perceptible etc., to reduce the amount of data that needs to be stored.

If you take a 320kbps file, re-encode it to 192kbps, then re-encode it again to 320kbps, the output file from the 320kbps can only be as good as output from the 192kbps encode. If the 192kbps encode lowered the quality of the audio (perceptual or otherwise), when you re-encode it to 320kbps it will obviously encode the lower quality output.

There really isn't a way to know whether an audio file has been re-compressed unless you can compare the 320kbps file with an original copy of the source. If there were encoding artifacts introduced with a 192kbps encode, it may be possible to detect them (of course, you may be able to hear them), but you wouldn't know whether that was a result of a re-encode or from the source. Likewise, if it seems that there is extra bitrate than required for the audio, you wouldn't know whether thats a re-encode or source related, as the audio may simply not require 320kbps.

As you suggest, re-encoding to 320kbps is absolutely pointless, unless an audio format change is necessary. An MP3 file encoded to 320kbps is pretty high anyway, but of course the quality of the encode depends on the encoder used. People are still using ancient mp3 encoders, or mp3 encoders that are simply bad, and these are definitely noticeable (depending on the bitrate of course). Using the latest LAME 3.99A11 (as an example, LAME 3.98.x is exceptionally good too), VBR mode, the quality of a song with VBR ~160 can be superior to old or poor encoders at 192kbps, or even 224kbps or higher!

Basically, 320kbps mp3 is kinda pointless, as that suggests CBR which is excessibely wasteful, as silence utilises the same amount of data as complex audio scenes. A VBR file of ~192kbps (average) may have parts where its 32kbps, 64kbps etc, and when necessary fully utilise 320kbps.

In answer to your question, not really! Most of the video encoders out there are meant for ease of use, not so much quality. The only situation where CBR should be used is with streaming scenarios. Probably one of the advantages for anti-piracy is the fact that most people don't encode properly, use the wrong software etc. To encode a movie in anything other than Constant quality (unknown end size, although can be estimated. Stable quality across encodes no matter length), or ABR mode (2-pass encoding), where the best way is to encode the audio using VBR, and using the end file size encoding the video to certain bitrate, in 2-pass mode not CBR, taking into account container requirements (links the audio, video, subtitle channels and timings etc). For 2-pass encoding, the first pass is a fast data storage requirement check (essentially), which stores the analysis in a stats file which the second pass can use. Areas that require more bitrate, such as motion scenes, get that bitrate, and still scenes use only the bitrate required (balanced with the bitrate requirement for the other scenes of course).

Basically any encoded file with 320kbps MP3 audio hasn't been done correctly regardless of any other factors