Damaged AVI file by starting a Capture with AMCAP to a Loved file. Hours of Video is now 2 seconds

I used a program called AMCAP to record some video (with audio).
It starts by specifying a "Capture File"
It asks how much space to be "Pre-Allocated", and defaults to 1Mb.
It then grows to whatever size (in my case ~13Gb in ~5 hours)....

If you stop the capture after say 5 hours, the file is now xxx big.
If you then start capturing again, it uses the same name and whatever the size was, is now treated as pre-allocated space.

I accidentally started the capture again, realised and stopped it two seconds later.
The file is still xxx big as if there is 5 hours of video, but when you play it, the file is now two seconds long
The mission is to recover the missing Video (& Audio) that I assume is still completely intact.
Every player I try only sees the first two seconds
Basically I assume there is a header and the Length is now wrong and I need to edit it.
Any Suggestions or recommendations for a suitable utility that can recover the remaining data would be much appreciated?
If it helps, I don't care about the Video, but recovering the Audio is very important.

I believe the properties of the file are:-
The Image is 320 x 240 pixels
Duration 0:00:01 (Actual is probably close to 5 hours)
The Audio is 1411kbps  16bit PCM
The Video is 29fps
Data Rate is 14350kbps
Video sample size is 24 bit
Uncompressed
The current File Size is 13Gb representing about 5 hours

Many Thanks
John Pengelley
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