RaP: Workaround broken seeking in flv after red5 update.

Since the update to the newer red5, seeking in flv files (webcams in
particular are noticable) has been broken, resulting in cameras
appearing to "hang" any time there is a cut in the generated video -
which happens when start/stop button is pushed, or when cameras are
added or removed.

We can detect the problematic video files because the timestamp of the
first frame is large (old red5 versions always set first frame
timestamp to 0.001 seconds). If we see a file like this, having ffmpeg
remux the file - rewriting the timestamps and index - works around the
problem.