[MPlayer-dev-eng] [PATCH] further dvr-ms playback improvements

[Nico Sabbi]

John Donaghy wrote:

>
> The current version in SVN is fine for straight playback because it
> reads the average frame time from the container. This value is
> normally perfect in in all the recordings I have but it was wrong in
> my one HD sample, which is why I tried instead to calculate it. (In
> the file in question the average frame time was set to 0.0166833 in

59.94 fps

> what I think is a PAL format HD recording. That value is half the
> frametime of what an NTSC frame should be so maybe the recording was
> actually NTSC progressive scan but I dont know. And I dont know what
> the average frame time should be for progressive scan - presumably it
> is half??? I need more samples where I can be sure of the source).

the frame time doesn't depend on the progressiveness/interlacing
of the video, but on the framerate. For some time now, for some obscure 
reason,
many american broadcasters have been transmitting ntsc content
tricked (changing the repeat-* in the sequence headers) so as to make
the video stream look like encoded ad double the framerate.
The decoder will have to deal with this change somehow in order it to show
it correctly on tv (that accepts 59.94 _fields_ per second, not _frames_ 
per
second as  indicated by the sequence headers), and repeat the other field
when indicated in the stream, so what's the benefit of this abomination
is really beyond my understanding.
I guess you stumbled on a transmission of this kind

>
> Seeking will still not work correctly with the current version because
> you really need the frame number after the seek to set the correct PTS
> value based on the average frame time. I dont know if there's a way to
> calculate it though. The alternative is to use the file based PTS as
> the starting point after the seek and then start adding the average
> frame time but if the first file PTS value is significantly wrong then
> the audio and video might not be exactly in sync after a seek.


maybe ask microsoft. Isn't there any useful information in msdn? :)