Well, basically the problem is that Quicktime and keynote are not reproducing some AVI files.
The first thing I noted was that some AVI files didn't had a screenshot of the video in the thumbnail. After this, when trying to reproduce the video, a blackscreen appeared in quicktime. But, as you can notice in the screenshot, the time bar and the time stamp were "moving" (the video is being played, but a black screen in shown):
Of course, I can reproduce the video with some other program like VLC:
I can also reproduce the video if i convert the AVI file to an MP4 file (which of course, also shows the thumbnail):
Up to this moment, this was not a problem, as I could reporduce the videos in VLC if Quicktime didn't worked.
But now I noticed that, this AVI files cannot be inserted in Keynotes files either:
Which is a problem. Of course, this didn't happened before, and that's why I'm asking you if somebody had the same problem and how you fixed it.
I'm running Sierra 10.12.1. I'm not sure if a software update caused this problem, probably it was. I installed Perian but I had no luck with it.
Thank you for your time, hope you can help me.