I am using Mp3tag v3.00 to tag .m4a audio files and have noticed that the CRC32 of the audio data (note: I am not talking about the entire file's CRC32, I only mean the audio data which excludes the file metadata etc.) is different after tagging to what it was originally.
If it's significant, I am using dBpoweramp's "Calculate Audio CRC" encoder to calculate the checksums. I have never known this plugin to malfunction before, after thousands of uses, so I trust it.
Before tagging the .m4a files I notice that, according to Mp3tag, the contained tag before I make any alterations is "MP4 (MP4 Nero)" and after alterations it is now "MP4 (MP4)".
Regardless of how big or small the tag alteration is, or even if I select the "Optimize MP4" feature in Mp3tag without altering the tags, the resulting files all have the same audio checksum. It simply seems that any kind of change to the file changes the audio data in the same way.
I am very reluctant to proceed with tagging these files unless I am confident the audio data is unaffected. If Mp3tag is not capable of achieving this, please can someone suggest an alternative tool that will let me achieve this? If this not possible at all - with any tool - then can someone please explain why this is the case?
Thanks for any help.