Re: [FFmpeg-devel] Politics

["Daniel Cantarín" <canta@canta.com.ar>]

> 
> consider a subtitle track
> consider 2 video tracks for US 30000/1001 fps and EU 25 fps
> 
> the 6th frame in the US track is at  0.2002 sec, the 5th in the EU 
> track at 0.2sec
> 
> 
> if these differ and you want a subtitle to either stop displaying after 
> the
> earlier or begin displaying after the earlier reliably. Then you need a
> timebase that can represent points within each such close encounter of 
> frame
> times.
> 

So, this isn't a subtitle problem if subtitle timings are correct. You
let 0.2002 in the subtitle, players will decide the frame. You want to
match the frame with the content, then you transcode the video properly.
Am I losing something?

Then again, we're of course not discussing players. One may say "that's
not ffmpeg responsability", yet players are 90% of the time the main
reason we have to do any extra work with ffmpeg. If we discuss real
life scenarios, we should be discussing players.

I also fail to see why would somebody want a "frame-perfect" sync
between two videos with different FPS. That's absurd: there's no such
thing as "frame-perfect" in such scenarios. What you would want is video
timings to be honored. That is: FPS conversion to be faithful to video
timings and content. I can imagine such precision dealing with frames
being blurred and having to do lots of fine tuning in order to be able
to perceive a single frame off in subtitles. That would be the real
problematic situation, not any .0002 rounding.

So, I see your example as a case of "what would the player do with that
0.2002 rounding" (in which case, we all know there would be two
different subtitle files/streams with different precision for each
video if it's THAT important) instead of "we need to change the timebase
to something 4 decimals precise multiplier to both videos".

And even if this fails and a frame is interpreted incorrectly in the
player, good luck finding anyone saying anything about it: nobody cares
about a single frame when it's about subtitles. People watching
subtitles are simply not looking at that. This isn't speedrunning: it's
translating and transcribing. People wants to understand what's going on
in the screen, not debugging video frames.

So, I see no "serious subtitle problem" nor anything close to
"unnaceptable" here.

Let's remark, as softworkz say, this are all fantasy scenarios, and the
patchset doesn't show any real precision problem so far. If anyone is
willing to share input files to test such possible precision problems,
I'm willing to do the tests. No such files so far.


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