[FFmpeg-devel] [PATCH] RFC: Set reasonable subtitle dimensions for timed-text in mov/mp4.

Nicolas George nicolas.george at normalesup.org
Mon Mar 11 21:16:26 CET 2013

Le primidi 21 ventôse, an CCXXI, Philip Langdale a écrit :
> No. The extradata doesn't let you do that - the stream headers added by
> the muxer represent that.

Too bad.

> Then you don't see anything - which is what triggered the original bug
> report. It will render the subtitles in a 0x0 box in the top left
> corner :-/

Too bad again.

> Well, it means requiring a bunch more information. My proposal gives you
> reasonable results in the vast majority of cases. I agree that additional
> encoding options are probably necessary to give total control, but I'd
> like something that doesn't require it.
> It's very tedious if you're trying to do a simple remux to have to provide
> a bunch of options that are easily guessable in the normal scenario.

I am strongly opposed to doing this kind of thing in the demuxer. To me,
doing the correct thing in all cases is much more important than making the
usual situation more practical.

I would suggest the following course of action:

1. Make sure the encoder and the muxer do the right thing in all cases.
   Doing the right thing requires working in a completely predictable and
   controllable way.

2. Make sure the encoder has the options necessary to control these fields.

3. Implement the size-guessing heuristics in the application that calls the
   encoder (i.e. in ffmpeg.c), while still making sure it can be controlled
   by the user.


  Nicolas George
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