Corrupted m4a file from iPhone

Hi,

This is a data recovery case and not a forensic one one customer came to my office with a corrupted m4a file, which should contain a 1 hour interview that he had recorded on his iPhone.

The file could not be extracted from the iPhone using Mac OS X native tools, but the customer succeeded copying it from the iPhone using iExplorer.

We tried playing the file with miscellaneous softwares like VNC media player from videolan.org.
The file displayed a length of about 26 minutes but was corrupt and could not be played.

I then used faac.exe and faad.exe according to this procedure http//sysfrontier.com/en/2014/12/31/hello-world/ and got a valid audio file, with a duration of about 1 minute.

The original file is about 1 MB (1582 Ko).

I'm wondering if there is hope that the original file contains more "audio fragments" which would have been ignored by faac / faad, or if the duration of a 1 MB audio m4a file is typically around 1 minute.

Any other idea to possibly retrieve a longer m4a file from the iPhone without jailbreaking it is of course much welcome.

Thanks.