[FFmpeg-devel] [PATCH] check if channel layout matches number of channels

[Michael Niedermayer]

On Sun, Apr 19, 2009 at 12:17:32AM -0400, Justin Ruggles wrote:
> Michael Niedermayer wrote:
> > On Sat, Apr 18, 2009 at 07:41:14PM -0400, Justin Ruggles wrote:
> >> Hi,
> >>
> >> Currently the output channel layout is always set to the input channel
> >> layout, even when upmixing or downmixing.  This patch checks that the
> >> channel layout matches the number of channels.  If it does not, the
> >> output channel layout is set to 0.
> >>
> >> I put the function in audioconvert.c/h so that encoders and decoders can
> >>  also use it to validate the input.
> >>
> >> -Justin
> >>
> >>
> > 
> >> diff --git a/ffmpeg.c b/ffmpeg.c
> >> index 200d57d..c050512 100644
> >> --- a/ffmpeg.c
> >> +++ b/ffmpeg.c
> >> @@ -3212,6 +3212,8 @@ static void new_audio_stream(AVFormatContext *oc)
> >>          audio_enc->channels = audio_channels;
> >>          audio_enc->sample_fmt = audio_sample_fmt;
> >>          audio_enc->channel_layout = channel_layout;
> >> +        if (avcodec_channel_layout_num_channels(channel_layout) != audio_channels)
> >> +            audio_enc->channel_layout = 0;
> >>  
> >>          if(codec && codec->sample_fmts){
> >>              const enum SampleFormat *p= codec->sample_fmts;
> >> diff --git a/libavcodec/audioconvert.c b/libavcodec/audioconvert.c
> >> index b0a8afa..e4c9890 100644
> >> --- a/libavcodec/audioconvert.c
> >> +++ b/libavcodec/audioconvert.c
> >> @@ -153,6 +153,17 @@ void avcodec_get_channel_layout_string(char *buf, int buf_size, int nb_channels,
> >>      }
> >>  }
> >>  
> >> +int avcodec_channel_layout_num_channels(int64_t channel_layout)
> >> +{
> >> +    /* based on a public domain bit counting algorithm found at
> >> +       http://graphics.stanford.edu/~seander/bithacks.html */
> >> +    uint64_t v = channel_layout;
> >> +    v = v - ((v >> 1) & 0x5555555555555555ULL);
> >> +    v = (v & 0x3333333333333333ULL) + ((v >> 2) & 0x3333333333333333ULL);
> >> +    v = (v + (v >> 4)) & 0xF0F0F0F0F0F0F0FULL;
> >> +    return (v * 0x101010101010101ULL) >> 56;
> >> +}
> > 
> > this is not speed critical, not even close, so we prefer simple code over
> > fast code.
> > 
> > for(count=0; x; count++)
> >     x&= x-1;
> > return count;
> > 
> > is obfuscated enough
> 
> new patch attached with the simpler code.

ok

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Let us carefully observe those good qualities wherein our enemies excel us
and endeavor to excel them, by avoiding what is faulty, and imitating what
is excellent in them. -- Plutarch
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