Open broken cam file in any hex editor, I used to use XVI32. Magic header (red on screen under) is 12 bytes long, we need to keep it,

next 8 bytes is timestamp of first packet, which we need to remove.

So we selecting 8 bytes of 1st packet and the packet itself (red on screenshor) and we erasing it (delete block in XVI32).
Result:


Then just save the file and enjoy fixed cam.