[FFmpeg-devel] [PATCH] avfilter/buffersrc: fix overriding unknown channel layouts with negotiated one

[Marton Balint]

On Sat, 30 Mar 2024, James Almer wrote:

> On 3/29/2024 7:01 PM, Marton Balint wrote:
>>
>>
>>  On Sat, 23 Mar 2024, Marton Balint wrote:
>>
>>>  Fixes ffplay playback of unknown layouts, when SDL directly supports the
>>>  audio
>>>  format, such as:
>>>
>>>  ffplay -f lavfi anullsrc=cl=2C,aformat=s16
>>>
>>>  Without the patch, "Channel layout change is not supported" errors are
>>>  generated because buffersrc (unknown 2 channel) and buffersink (stereo)
>>>  negotiated a stereo layout, but the stereo layout was never stored in the
>>>  BufferSourceContext.
>>>
>>>  This fixes a regression of 7251f909721a570726775acf61b2b9c28a950c76, but
>>>  this
>>>  is more of a regression of the avfilter channel layout conversion
>>>  (1f96db959c1235bb7079d354e09914a0a2608f62).
>>>
>>>  Signed-off-by: Marton Balint <cus at passwd.hu>
>>>  ---
>>>  libavfilter/buffersrc.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>>  diff --git a/libavfilter/buffersrc.c b/libavfilter/buffersrc.c
>>>  index ddcd403785..fcae4f8e69 100644
>>>  --- a/libavfilter/buffersrc.c
>>>  +++ b/libavfilter/buffersrc.c
>>>  @@ -507,7 +507,7 @@ static int config_props(AVFilterLink *link)
>>>          }
>>>          break;
>>>      case AVMEDIA_TYPE_AUDIO:
>>>  -        if (!c->ch_layout.nb_channels) {
>>>  +        if (!c->ch_layout.nb_channels || c->ch_layout.order ==
>>>  AV_CHANNEL_ORDER_UNSPEC) {
>>>              int ret = av_channel_layout_copy(&c->ch_layout,
>>>  &link->ch_layout);
>
> Why is this the only field in the function where BufferSourceContext is the 
> destination and the link is the source?

I guess the reason for that is that those link parameters are not 
negotiated, so they has to be set. Storing the negotiated layout on the 
context has a different purpose and is originated from 01649c79c87.

Regards,
Marton