[FFmpeg-devel] [PATCH] Add documentation for -ast, -vst, -sst

[Stefano Sabatini]

On date Friday 2009-02-27 17:19:30 -0500, Ronald S. Bultje encoded:
> Hi,
> 
> On Fri, Feb 27, 2009 at 4:18 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Fri, Feb 27, 2009 at 03:26:19PM -0500, Ronald S. Bultje wrote:
> >> On Thu, Feb 26, 2009 at 2:43 PM, Stefano Sabatini
> >> <stefano.sabatini-lala at poste.it> wrote:
> >> > On date Tuesday 2009-02-24 23:50:40 +0100, Stefano Sabatini encoded:
> >> >> + at item -ast @var{audio_stream_number}
> >> >> +Select the desired audio stream number, counting from 1.
> >>
> >> This has confused me all too often. Can we change this so it counts
> >> like a regular number from 0?
> >
> > yes
> 
> that piece of code is full of crap btw, <0 for subtitles is seen as
> "disable" but <0 for audio/video isn't. I added that also, which makes
> the subtitle/video/audio selection code more alike. This would also
> allow to remove -an/-vn at some point but that could also be done
> after the release.
> 
> if you think this changes too much, I'll just apply the
> "wanted_x_stream < 0" to "wanted_x_stream <= 0" *3 change.
> 
> Stefano, can you regen your documentation patch with this change taken
> into account and apply that also?

Hi, thanks for noticing the issue, yes the code as it is is greatly
obfuscated and subtlely broken.

I split your patch and done more simplifications.
Summary:

* ffplay-fix-sst-logic.patch
  When the user selects the subtitle stream N, if N is not 0 then it
  is always selected N-1.
  Patches fixes this.

* ffplay-simplify-sst-logic.patch
  Simplify the logic, using the following reasoning:

  A & B & (C | A) =
  A & B

  since if A & B then A is always true so (C | A) is always true.
  Formal derivation below:

  A & B & (C | A) =
  (A & B) & (C | A) =
  (A & B & C) | (A & B & A) =
  (A & B & C) | (A & B) =
  A & B

  Thus the third condition (subtitle_index < 0) is unnecessary.

* ffplay-consistent-ast-vst.patch
  Make the -ast and -vst behaviour consistent with that of -sst, that
  is count starts from 0 and negative values are interpreted as
  "disable".

* ffplay-document-xst.patch
  Document the -ast, -vst, -sst options according to the new
  (sane) behaviour.

Regards.
-- 
FFmpeg = Fundamentalist and Faboulous Murdering Portentous Erroneous Gem
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