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

Roman Shaposhnick rvs
Wed Apr 18 04:07:18 CEST 2007

On Sun, 2007-04-15 at 14:28 -0700, Trent Piepho wrote:
> On Sun, 15 Apr 2007, Roman Shaposhnik wrote:
> >   Trent, would you be able to help me out with understanding the
> > following, please: here's my problem -- we have a physical objective
> > process of capturing frames, in the NTSC world each frame lasts
> > exactly 1001/30000 seconds (and again -- this is an objective precise
> > number). So, given these facts it'll be fair to say that:
> [...]
> > BUT when we turn to the frame #1019, which occupies
> > an interval of:
> >      [1019*1001/30000; 1020*1001/30000) == [34.0006; 34.03)
> > and is SUPPOSED to be recorded during the 34th second,
> > it still has a timecode of 00:00:33:29 !!!!!!
> >
> >    Now, from that point on -- timecode LIES to us. Why ?!?!?
> I think the key thing to understand about timecode is that it's not for
> timing.  It's not used to control playback speed, or synchronize audio, or
> control how much time something takes to play.  It is not used at all for
> decoding or playback.  It is used externally for editing and cueing.
> The name timecode is confusing.  It would be better to call it "SMPTE Frame
> ID".

  I think I understand it better now. Thanks for the explanation. My
biggest concern was that in the scenario I gave a frame that was
captured during 34th second appears as 00:00:33:29. I was ready to
NOT trust the frame counter but it appears that a second counter is
not to be trusted either. As you say -- its just an ID anyway, so as
long as different frames have different IDs I'm happy. Besides,
the error is small so even for cueing it works ok.

> It's like saying each calendar day is 1/365th of a year.  So after 365 days
> the Earth should be in the same point in its orbit as it started at.  But
> the Earth is not in the same place in its orbit on 01-01-2007 as it is was
> 01-01-2006!  Our calendar lied to us!  No, not really.  The calendar counts
> days, the Earth's rotations.  It tells us that 365 days elapsed between
> 01-01-2006 and 01-01-2007, and that's right.

  A bit of an offtopic, but I couldn't resist: with Earth it is even
worse. Because it is part of a Solar system it get influenced by other
planets. Hence the biggest trouble with the year is not even that
it can't be measured in days, but that its duration is not constant.
Each year is just a little bit different from the other one, depending
on where other Solar bodies were.


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