[mythtv-users] is it really 29.97 fps or 24 fps?

Brian J. Murrell brian at interlinx.bc.ca
Fri Sep 3 02:55:27 UTC 2010


When I play a recording of a given television show (a drama, so filmed
on real film, not video tape) recorded from clearqam with mplayer, it
says about it:

VIDEO:  MPEG2  720x480  (aspect 2)  29.970 fps  15000.0 kbps (1875.0 kbyte/s)
[V] filefmt:29  fourcc:0x10000002  size:720x480  fps:29.970  ftime:=0.0334

Yet if I step through it a frame at a time with `.' I can see quite
clearly that it's (a) not interlaced but progressive and (b) that there
are 24 frames in every second played.

So that seems to make it quite obvious that the MPEG that my cableco
sends is the original 24fps progressive frames from film.  I guess the
expectation is that whatever is displaying that to a CRT TV will
telecine it.  But I digress.

What I find interesting is that mythfrontend plays this content as 29.97
fps, even to my plasma display which is quite capable of a 24 fps
refresh rate.

Indeed, given another file which mplayer reports as:

VIDEO:  [XVID]  624x352  24bpp  23.976 fps  912.1 kbps (111.3 kbyte/s)
Auto-selected AVI audio ID = 1
[V] filefmt:3  fourcc:0x44495658  size:624x352  fps:23.976  ftime:=0.0417

and I can step through and see is progressive and count 24 fps,
mythfrontend does change the refresh rate to 24 fps on my display and
does display 24.

So what's the deal with the clearqam recorded MPEGs?  Why can mplayer
figure out they are 24fps (despite the header saying otherwise) and yet
mythfrontend cannot?

b.

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