[FFmpeg-devel] [PATCH] ffmpeg should look up AVCodec by name

[Aurelien Jacobs]

Michael Niedermayer wrote:

> On Mon, Oct 06, 2008 at 02:19:57AM +0200, Aurelien Jacobs wrote:
> > Michael Niedermayer wrote:
> > 
> > > On Mon, Oct 06, 2008 at 01:22:09AM +0200, Aurelien Jacobs wrote:
> > > > Hi,
> > > > 
> > > > Curently, when specifying a codec with -[asv]codec to ffmpeg, it is
> > > > first converted to a CODEC_ID_* and then the coresponding AVCodec
> > > > is picked up. Problem arise when we have several AVCodec handling the
> > > > same CODEC_ID_*. eg: -acodec libvorbis select the internal vorbis
> > > > encoder instead of the libvorbis one...
> > > > Attached patch ensure we pick up AVCodec using the codec name, when
> > > > available. This allows to actually select the libvorbis encoder for
> > > > example. This works for both input and output codecs. This also
> > > > correctly display the selected codec.
> > > > 
> > > > Aurel
> > > 
> > > > Index: ffmpeg.c
> > > > ===================================================================
> > > > --- ffmpeg.c	(revision 15552)
> > > > +++ ffmpeg.c	(working copy)
> > > > @@ -1915,7 +1915,9 @@ static int av_encode(AVFormatContext **output_file
> > > >      for(i=0;i<nb_ostreams;i++) {
> > > >          ost = ost_table[i];
> > > >          if (ost->encoding_needed) {
> > > > -            AVCodec *codec;
> > > > +            AVCodec *codec = ost->st->codec->codec;
> > > 
> > > > +            ost->st->codec->codec = NULL;
> > > 
> > > why?
> > 
> > Because avcodec_open() fails if it's not NULL.
> > I guess the reason is to prevent calling avcodec_open() twice for the
> > same AVCodecContext.
> > Maybe avcodec_open() could be modified to not check this...
> 
> I do like to keep double call detection ...

OK.

> > > besides the solution looks hackish
> > 
> > In a way, it is, because it misuse ost->st->codec->codec to convey
> > the AVcodec selection inside ffmpeg.c.
> > But I haven't found a better way to convey this simply. At the time
> > the audio_codec_name is parsed, the corresponding AVInputStream is
> > still not allocated/initialized, so it can't be used. And when
> > AVInputStream is allocated, audio_codec_name is not available
> > anymore. But still this information must be conveyed on a per stream
> > basis.
> 
> why dont you use a static array?

That's indeed another possibility...
Done that way.

> > > and i think ive seen a similar patch already from someone else ...
> > 
> > I don't remember about this.
> 
> somewhere in the thread with subject
> "[FFmpeg-devel] [PATCH] Codec lookup: do not use codec_id"
> i think

Got it. I didn't remembered about it, and despite this, my patch was
really quite similar to the one of this old thread...
One difference is that my patch also allows selecting input codecs
by name (not only output codecs).

Attached an updated patch (the libavcodec/utils.c hunks are meant to
be applied separately).

Aurel
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