[FFmpeg-devel] [DEVEL][PATCH] ffmpeg: fix channel_layout bug on non-default layout

[Michael Niedermayer]

On Thu, Nov 09, 2017 at 09:37:33PM +0100, pkv.stream wrote:
> Hi Michael,
> 
> >>  ffmpeg_opt.c |   11 ++++++++++-
> >>  1 file changed, 10 insertions(+), 1 deletion(-)
> >>2af07f4366efdfaf1018bb2ea29be672befe0823  0001-ffmpeg-fix-channel_layout-bug-on-non-default-layout.patch
> >> From 4ec55dc88923108132307b41300a1abddf32e6f7 Mon Sep 17 00:00:00 2001
> >>From: pkviet <pkv.stream at gmail.com>
> >>Date: Mon, 2 Oct 2017 11:14:31 +0200
> >>Subject: [PATCH] ffmpeg: fix channel_layout bug on non-default layout
> >>
> >>Fix for ticket 6706.
> >>The -channel_layout option was not working when the channel layout was not
> >>a default one (ex: for 4 channels, quad was interpreted as 4.0 which is
> >>the default layout for 4 channels; or octagonal interpreted as 7.1).
> >>This led to the spurious auto-insertion of an auto-resampler filter
> >>remapping the channels even if input and output had identical channel
> >>layouts.
> >>The fix operates by directly calling the channel layout if defined in
> >>options. If the layout is undefined, the default layout is selected as
> >>before the fix.
> >>---
> >>  ffmpeg_opt.c | 11 ++++++++++-
> >>  1 file changed, 10 insertions(+), 1 deletion(-)
> >>
> >>diff --git a/ffmpeg_opt.c b/ffmpeg_opt.c
> >>index 100fa76..cf5a63c 100644
> >>--- a/ffmpeg_opt.c
> >>+++ b/ffmpeg_opt.c
> >>@@ -1804,6 +1804,12 @@ static OutputStream *new_audio_stream(OptionsContext *o, AVFormatContext *oc, in
> >>          MATCH_PER_STREAM_OPT(audio_channels, i, audio_enc->channels, oc, st);
> >>+        AVDictionaryEntry *output_layout = av_dict_get(o->g->codec_opts,
> >>+                                                       "channel_layout",
> >>+                                                       NULL, AV_DICT_MATCH_CASE);
> >This doesnt look right
> >
> >not an issue of the patch as such but
> >why is the channel_layout option per file and not per stream?
> 
> 
> just my ignorance; do you mean this is not the right way to retrieve
> the channel_layout option from an audio stream ?

I think there is more buggy with how the channel_layout is handled

try this:
./ffmpeg -i ~/videos/matrixbench_mpeg2.mpg -channel_layout 5 test.wav
and this:
./ffmpeg -i ~/videos/matrixbench_mpeg2.mpg -channel_layout:a 5 test.wav

while it may appear that the are both working this is deceiving.
I think only the channel number gets actually used in the 2nd case

Look at what your code with av_dict_get() reads.
It does not obtain the 5 in the 2nd case

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

Never trust a computer, one day, it may think you are the virus. -- Compn
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