I just wrote a video file with GStreamer and I can't play it in any video player

You need to add -e it's always -e.

Ok the reality of the debugging steps:

• First check if there is any legitimate amount of data in the output file, this can normally be done by running ls -l and checking to see if there are more than a few bits
• If there is actual data, and you still can't read it make sure that you're closing the file stream!!
  • If this is in the command line add -e to the end of the commend. This will make sure that the file is closed properly. If the file is not closed properly, other video players will hate you.
  • If you're using a library like OpenCV VideoWriter make sure to run .release to finish your stream
  • If you're doing anything else find the equivalent and make sure to do it

Even after closing it properly you might still not be able to preview it - your pipeline is probably still busted. However, checking that it is closed properly is step one and should always be step one.

I'm also a big fan of the videotestsrc