Finalize a .mp4 movie after simplescreenrecorer crashed?

[ronneber]

First a big thanks for providing this excellent piece of work. I use simplescreenrecorder every week to record my lectures. But today it crashed and left an .mp4 file which is not playable. Is there a way to fix this file? I think the content is in it (it has a size of 28MB for approx. half an hour slides with audio).
Best regards,
Olaf

[iamgreaser]

My advice in future would be to use Matroska (MKV) for your container format - it's still H264, but it doesn't require some crap at the end of your file. I've had SSR crash on me before, but at least I was able to play the resulting MKV file.

As for recovering the mp4 data, I'm not sure what to do - I guess you could try to play it as raw AAC (or whatever .mp4 can handle for audio / whatever you used for audio) and that would at least get the audio out of it... there will be a fair bit of garbage, but it might just do the trick.

[MaartenBaert]

Have you any idea why SSR crashed? Which version are you using, and which distribution? This is not normal. Did it actually crash, or did you just get an error message? SSR saves logs in ~/.ssr/logs, did those show anything unusual?

Regarding MP4 repair, the thing you should look for is recovering the mp4 'moov atom'. Some googling turned up this:
http://vcg.isti.cnr.it/~ponchio/untrunc.php
Not tested, I have no idea how well this works. As iamgreaser suggested, use MKV whenever possible to avoid problems like this.

[MaartenBaert]

For future reference, there is now a fork of untrunc which works quite well at least in my tests:

https://github.com/anthwlock/untrunc

Even if it works, you may find that the file has issues, e.g. video and audio may be out of sync. The tool has some options to try to correct this.

Still, the best way to avoid this problem is to use MKV instead, then the repair process is much easier and more reliable.