On Mon, Oct 26, 2015 at 8:42 PM, Mel Matsuoka <[email protected]> wrote:
> > > > On Oct 26, 2015, at 9:15 AM, Carl Eugen Hoyos <[email protected]> wrote: > > > > I believe (strongly) that what you like as output > > framerate is not 29.97 but 30000/1001 > > > Hi Carl, > > I guess I'm looking for the "why", rather than the "what", as far as this > syntax is concerned. > > In NTSC broadcast land, 29.97 frame rate is *always* defined and referred > to as just that: 29.97. No professional video tool that I'm aware of > requires the user to define that frame rate with the level of precision > that dividing 30000 by 1001 gives you. > > And I suppose this begs the question, where do the numbers 30000 and 1001 > come from to begin with? > > Just some heuristics. As explained by Moritz, the correct rate is 30000/1001 due to its analogue heritage and most tools (software, cameras) I know produce timestamps (and thus a frame rate) based on that. However, some don't. E.g. Final Cut Pro 7 and earlier and most Apple Tools from that time even used the rounded version 29.97 in the files they produced. In theory the difference is so marginal, that it should not cause problems (it takes more than nine hours for the rounding difference to produce 1 frame A/V desync if a tool interpretes a 29.97 file as 30000/1001 which definitely happens in some cases). My experience has been, that the safer side is to use 30000/1001, simply because more tools use it and even Apple's new tools (like FCPX use 30000/1001 internally). You will probably not run into these problems if you use 29.97 but if you do, errors might be very subtle and hard to diagnose. _______________________________________________ ffmpeg-user mailing list [email protected] http://ffmpeg.org/mailman/listinfo/ffmpeg-user
