[Ffmpeg-devel] [PATCH] remove drop timecode flag

[Michael Niedermayer]

Hi

On Sun, Apr 15, 2007 at 10:49:17AM -0700, Trent Piepho wrote:
> On Sun, 15 Apr 2007, Michael Niedermayer wrote:
> > On Sun, Apr 15, 2007 at 08:27:55AM -0700, Trent Piepho wrote:
> > > On Sun, 15 Apr 2007, Michael Niedermayer wrote:
> > > >
> > > > attached patch removes the drop timecode encoding support
> > > > reasoning is that iam not aware of any use (not even obscure) of this feature
> > >
> > > Isn't the timecode wrong if you don't use drop frame timecode for NTSC?
> > >
> > > e.g., the timecode after exactly 1 hour of NTSC video will be
> > > '00:59:56:12', which is short 3 seconds and 18 frames from one hour.  With
> > > drop frame timecode, the timecode after an hour would be '01:00:00:00',
> > > since 108 timecodes would have been skipped over.
> >
> > timecodes are codec specific
> > if a codec uses the rounded up fps as timebase then the timecode must be
> > scaled accordingly and if needed the drop flag be set, its not the user
> > applications job to do this
> 
> SMPTE timescodes are hour:minute:second:frame and should be unique for each
> frame.  The frame wraps from 29 to 0.  E.g., after '0:0:0:29' follows
> '0:0:01:00'.
> 
> In non-dropframe timecode, the timecode is incremented by one after each
> and every frame.  If you start at 0 and increment the counter 107892 times,
> it will end up at '00:59:56:12'.  This is just simple counting.
> '00:00:00:00' then '00:00:00:01', '00:00:00:02', and so on.
> 
> Think of the timecode as the frame number.  Not the frame PTS time, but
> just the ordinal number of the frame.  Instead of writing it in base 10,
> it's written in a weird base 30/base 60 numeric format.  It is convenient
> for humans to look at, since we keep time in base 60.
> 
> 107892 == 0x1a574 == 00:59:56:12, it's all the same, just an integer
> written in different formats.
> 
> The problem is that a broadcast of 107892 frames will last one hour, not 59
> minutes 56 seconds and 12 frames.  A broadcaster would like it if he could
> cue his tape to end after an hour by using a timecode of '01:00:00:00' in
> his automatic cueing equipment.

well iam not entirely sure what mpeg2 mandates in the non drop frame case
but mpeg4 requires 01:00:00:00 after an hour no matter if 30000/1001
fps or 12.5 fps or anything else, mpeg4 does not even support drop timecode

now if mpeg2 behaves the same (it doesnt seem so) then we have no problem
at all, if it differs then timecode is codec specific and IMHO its not
the users job to know these details, if this is really needed it belongs
into the encoder

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Freedom in capitalist society always remains about the same as it was in
ancient Greek republics: Freedom for slave owners. -- Vladimir Lenin
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