I am using ffmpeg to get renditions of different formats for videos. It uses Update DAM Asset workflow to transcode videos. But some times some videos will be failed to get their renditions.
Have anyone come across the same situation and if please let me know what would be the cause?
That is possible. Not all video will be transcoded correctly. You will see error in error log for those videos. Make sure that you use latest version of FFMPEG and you have all libraries installed. You can also try manual transcoding of failed videos (Using command line) and see if that works. You can also test if transcoding of a video succed using tool under http://localhost:4502/miscadmin#/etc/dam/video
If your site is video intensive, I would suggest to use third party video service like (Scene7 or Britecove ... many more)