Improve ffmpeg error reporting and replay logic.

[Former user]

2 requests.

1. When ffmpeg crashes with return code 1!, it should be possible to provide the actual ffmpeg error messages in the log. This would allow users and others trying to help them in the forum, to determine the problem without having to request/run/attach the manual ffmpeg command output.

2. After an ffmpeg crash with return code 1!, Serviio reports the failure, but then if the play attempt is repeated, Serviio thinks the transcoded file already exists and will not attempt to transcode again. This creates problems when the failure is due to a temporary condition, such as stream errors, or a file that has been renamed prior to a database refresh.

See http://forum.serviio.org/viewtopic.php?f=7&t=7411&view=unread#p52680 for an example log showing a failure followed by a replay.

[Former user]

It would also be very useful if the ffmpeg version could be reported in the log on a return code 1 or when Serviio checks for ffmpeg on startup.

[Petr Nejedly]

Might also check the version and compare to the min. supported version, to help solving FFmpeg problems on linux.

[Petr Nejedly]

Point 1) implemented for 1.2.1

[Petr Nejedly]

2 finished for 1.3, also prints out FFMpeg version