Update: I discovered several other recordings which had 21 kb in size, also f4v but with only sound, nellymoser. I did not get any error in logs or event viewer which makes it tough to debug! What could cause such a thing? I understand that there is no data recorded in the stream file, except metadata probably. I tried to convert such a file with ffmpeg and got an error saying there is no stream data found in file.
The method we use for publishing/recording is the following: the stream is published from the client in live mode (no record at all). On the server side, I create a new Stream and attach the publishing stream to it. Then I record the new stream. It seems to be working great in most cases but sometimes, for unknown reasons, it does not work.
Anybody, an idea?