out_21.avi
file created: 2009-05-24 14:09
file size: 514 MB (538,972,160 bytes)
Its kinda sad. We drove over 4 states (5 if we count montana) for over a day (another half to get to old faithful), setup my equipment, and when the recording of the eruption was almost over, I tripped over my own cables which caused this laptop to crash to the floor while recording the video to crash , with the battery pack disengaged.
Maybe its one of those times my heart dropped together with my items, but since the rugged laptop still manage to boot, and some hope lied within me that I would be able to recover the video one day. While I thought streaming broken video files were no big deal, it wasn’t so easy. My usual tools- media player classic, virtualdub, videolan etc were unable to play this file at all. It wasn’t until yesterday I attempted to rescue this file again.
1st I tried this open source “DivFix++ is #1 AVI Video Repair & Preview Utility” called DivFix++. While it managed to detect FourCC frames, the resulting video file was still unplayable. Okay let’s take a step back. Then because the Canon 40D I was using have officially has no video features, I used the open source EOS Video Record which allowed some form of video recording if the camera was tethered to a pc.
EOS Movie Record saves the resulting video in a MJPG format, so I tried figuring if JPGs could be extracted from the motion video file. I tried looking for MJPG2JPEG converters but none existing other than 2 examples of source codes here and here. I also started to examine and studying the file structures of AVIs, RIFF, JPEG etc, and with the help of a hex editor (the freeware HxD works great ), started digging around the file.
So when I’m peeking around the file at HEX Offset 04F0000 or human friendly number 75431936, the viewer showed full of zeros. Not a good news, because it meant there was not data beyond that point (buffer were not flush). From my estimation, based on file sizes, what was an approximately 2minute video is probably a sub 20s video. Which makes me feel like rewriting the subject as: “repairing a broken heart”, but read on…
I noticed DivFix++ almost generated a 75MB file which i meant it must have found the same errors I suspected and strip them off. So using the software did not entirely gone to waste. On examining the headers of the file, I found it empty which is a pretty good reason that nothing could play this file. I then remembered that EOS Movie Record writes the video headers only after recording. So following the avi riff structure, I copied in header values like frame rate, resolution etc, and eureka, the video became playable.
So, its not too sad and not all’s lost. The badly abused laptop (actually my mom’s and the 1st laptop I used much) still survived, I managed to recover 16s, and learn a couple of things about video file formats. And my photography apprentice of that day Ben Chua did took some photos with my spare camera.
p.s. You might be able to see the short segment of the recovered video below.
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