[mythtv] Video OSD Length and Mpeg Telecine.

[Michael T. Dean]

On 01/18/2009 09:46 PM, Bill Stewart wrote:
> Many/most of my mpegs show the incorrect length in the OSD during 
> playback.  The actual time of the movie if timed by a stopwatch is 
> correct, but the OSD time shown is not.
>  
> This is because the mpegs are telecine encoded.  The mpeg header 
> indicates the movie is 29.97fps, where as the actual frame rate is 
> 24fps because the repeat flag is set that indicates to the playback 
> device to repeat one frame for every four frames. 
>  
> Myth plays back the video correctly and I assume inserts the redundant 
> frame.  However, when counting frames in NuppleVideoPlayer.cpp / 
> tv_play.cpp, it does not count the redundant frame because it doesn't 
> exist in the file (video playback device is to repeat the last of each 
> 4 frames).  As such that total time and running time of the movie 
> shown in the OSD is in error by 4/5.
>  
> Normally mythtv caculates the time played as framesPlayed / 
> video_frame_rate. I have a simple patch that comestically corrects 
> this by scaling the OSD times by length*frames_playes/total_frames, 
> where length is the length reported in the mpeg header.  Normally myth 
> calculates this from the position map, but I also override this if the 
> length in the header is greater than that calculated by the position map.
>  
> Before submitting a ticket, I thought to run this by the devs in the 
> list first.

It's a known issue that's basically covered by #799 ( 
http://svn.mythtv.org/trac/ticket/799 ) and also affects any video whose 
frame rate changes within the stream.  Remember when looking at the 
ticket that anything written by a non-dev should not be determined to be 
"final authority" (i.e. the "doubled recording length", as well as 
plenty of info in comments, can be ignored)

Mike