With video cameras being completely ubiquitous and GoPro cameras able to be mounted pretty much anywhere, lots of GA pilots now like to make videos of their own flights. A passenger's cell phone video was used as supporting evidence in the Germanwings crash. Have there been any situations so far where a GA crash has been puzzling to investigators until they watch the video from the pilot's camera which shows the cause clearly? Are they even allowed to do this (anywhere, but NTSB in particular) or are there privacy regulations which prevent them from doing so?
The NTSB will use anything and everything available to them in their investigation, though release of certain materials is prohibited by law (e.g. CVR contents are not released, only transcripts).
I believe the NTSB is observing a similar protocol for onboard video: A synopsis is released (including a transcript of conversations) when requested, but the actual video is kept confidential by the agency -- I am not certain in that though, and the NTSB press office could provide a more detailed answer on their rules surrounding cockpit video / audio in GA crashes.