Salvaging mystery video file, convert to avi? help/advice?

[RootlessAgrarian]

I have a problem to solve: someone gave me 2 video files of the form

Code: Select all

name.avi

but only one of them was playable. Both were allegedly about 1 hr 20 in length; they were of almost identical size; the first one did indeed play to that length, but the other would fail every time (VLC popped up and instantly exited). On examining the files with basic command line tools I found that the first one was a valid AVI file (though VLC felt it needed repair); the other one was just "data", would not start, showed up as zero length, and could not be repaired.

Well, I banged my head on that file. I thought perhaps the sender had brutally chopped a longer AVI file in half w/o repackaging, so tried concatting the two files and re-repairing the headers with VLC. Nope. The repair got to exactly halfway through and ended, and the resulting 2x size file was playable for exactly 1 hr 20 minutes (i.e. only file 1).

After a while it struck me that maybe the sender had converted file 1 to avi but failed to convert file 2 -- it might be in some other format contrary to the file extension. So I started trying different file extensions on file 2 to see if I could use a different codec. Eventually I got around to m4v and Bingo, the result was (sort of!) playable. There was no audio and intermittent tiling (large rectangles that did not update or were b&w) but after a minute or two it settled down and I could see content. So I tried converting it to AVI using VLC -- I wasn't sure what I was doing, as this was my first attempt at using VLC to convert. It sorta worked, but not really; wouldn't play, and any click on the scrub control caused the playback window to close.

I tried various variations on codecs in the VLC convert Custom parameters, but I don't really know what I'm doing so it's basically a waste of time. I tried the GSpot app to see if it could analyze the file, but it hasn't got a clue about the corrupt file_2. Original author seems to have labelled it DivX, but as far as I can tell that's just another mp4 variant. This really is a maze of twisty little passages if you are not familiar with the underlying technology

Alas, this is my first foray into struggling with video formats so forgive my ignorance... is there a standard checklist of things to try when attempting to repair a damaged (or unidentifiable) video file? Anything else I can do (other than give up)?

[Jean-Baptiste Kempf]

Try mediainfo to analyze the file.