Re: [FFmpeg-devel] [PATCH] avformat/pcmdec: add support to set channel layout

From: James Almer <jamrial@gmail.com>
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH] avformat/pcmdec: add support to set channel layout
Date: Fri, 18 Mar 2022 15:32:02 -0300
Message-ID: <54aa664c-cc91-1f18-511d-e63c59cf7b86@gmail.com> (raw)
In-Reply-To: <20220318182458.64311-1-onemda@gmail.com>

On 3/18/2022 3:24 PM, Paul B Mahol wrote:
> Signed-off-by: Paul B Mahol <onemda@gmail.com>
> ---
>   libavformat/pcmdec.c | 13 ++++++++++++-
>   1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/libavformat/pcmdec.c b/libavformat/pcmdec.c
> index c7da740541..775cda8cc7 100644
> --- a/libavformat/pcmdec.c
> +++ b/libavformat/pcmdec.c
> @@ -22,6 +22,7 @@
>   #include "config_components.h"
>   
>   #include "libavutil/avstring.h"
> +#include "libavutil/channel_layout.h"
>   #include "avformat.h"
>   #include "internal.h"
>   #include "pcm.h"
> @@ -33,6 +34,7 @@ typedef struct PCMAudioDemuxerContext {
>       AVClass *class;
>       int sample_rate;
>       int channels;
> +    char *ch_layout_str;
>   } PCMAudioDemuxerContext;
>   
>   static int pcm_read_header(AVFormatContext *s)
> @@ -41,6 +43,7 @@ static int pcm_read_header(AVFormatContext *s)
>       AVCodecParameters *par;
>       AVStream *st;
>       uint8_t *mime_type = NULL;
> +    int ret;
>   
>       st = avformat_new_stream(s, NULL);
>       if (!st)
> @@ -50,7 +53,14 @@ static int pcm_read_header(AVFormatContext *s)
>       par->codec_type  = AVMEDIA_TYPE_AUDIO;
>       par->codec_id    = s->iformat->raw_codec_id;
>       par->sample_rate = s1->sample_rate;
> -    par->ch_layout.nb_channels = s1->channels;
> +    if (s1->ch_layout_str) {
> +        ret = av_channel_layout_from_string(&par->ch_layout,
> +                                            s1->ch_layout_str);
> +        if (ret < 0)
> +            return ret;
> +    } else {
> +        par->ch_layout.nb_channels = s1->channels;
> +    }
>   
>       av_opt_get(s->pb, "mime_type", AV_OPT_SEARCH_CHILDREN, &mime_type);
>       if (mime_type && s->iformat->mime_type) {
> @@ -99,6 +109,7 @@ static int pcm_read_header(AVFormatContext *s)
>   static const AVOption pcm_options[] = {
>       { "sample_rate", "", offsetof(PCMAudioDemuxerContext, sample_rate), AV_OPT_TYPE_INT, {.i64 = 44100}, 0, INT_MAX, AV_OPT_FLAG_DECODING_PARAM },
>       { "channels",    "", offsetof(PCMAudioDemuxerContext, channels),    AV_OPT_TYPE_INT, {.i64 = 1}, 0, INT_MAX, AV_OPT_FLAG_DECODING_PARAM },

This option should be deprecated here and in every other raw demuxer in 
favor of a new ch_layout one like the one you're introducing, and the 
code in ffmpeg.c looking for them adapted.

> +    { "ch_layout",   "", offsetof(PCMAudioDemuxerContext, ch_layout_str),AV_OPT_TYPE_STRING, {.str = NULL}, 0, 0, AV_OPT_FLAG_DECODING_PARAM },

AV_OPT_TYPE_CHLAYOUT. That way you don't need to bother with 
av_channel_layout_from_string(), and use av_channel_layout_copy() instead.

>       { NULL },
>   };
>   static const AVClass pcm_demuxer_class = {
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