On 12/10/2024 9:06 PM, Scott Theisen wrote:
On 12/9/24 02:30, Anton Khirnov wrote:Quoting James Almer (2024-11-30 14:41:20)On 11/14/2024 1:37 AM, Scott Theisen wrote:When attempting to upstream this MythTV change in September 2022, it was recommended touse AV_CHANNEL_ORDER_CUSTOM with two AV_CHAN_FRONT_CENTER channels. Seehttps://patchwork.ffmpeg.org/project/ffmpeg/ patch/20220921192611.3241-1-scott.the....@gmail.com/--- libavcodec/audiotoolboxdec.c | 4 ++-- libavcodec/mpegaudio_parser.c | 12 +++++++++--- libavcodec/mpegaudiodecheader.c | 4 +++- libavcodec/mpegaudiodecheader.h | 2 +- tests/ref/fate/pva-demux | 2 +- 5 files changed, 16 insertions(+), 8 deletions(-)diff --git a/libavcodec/audiotoolboxdec.c b/libavcodec/ audiotoolboxdec.cindex 0f7ce8e4eb..d279d7bbc4 100644 --- a/libavcodec/audiotoolboxdec.c +++ b/libavcodec/audiotoolboxdec.c@@ -346,10 +346,10 @@ static av_cold int ffat_create_decoder(AVCodecContext *avctx,avctx->codec_id == AV_CODEC_ID_MP2 || avctx->codec_id == AV_CODEC_ID_MP3)) { enum AVCodecID codec_id; - int bit_rate; + int bit_rate, dual_mono;if (ff_mpa_decode_header(AV_RB32(pkt->data), &avctx- >sample_rate, &in_format.mChannelsPerFrame, &avctx->frame_size,- &bit_rate, &codec_id) < 0)+ &bit_rate, &codec_id, &dual_mono) < 0)return AVERROR_INVALIDDATA; avctx->bit_rate = bit_rate; in_format.mSampleRate = avctx->sample_rate;diff --git a/libavcodec/mpegaudio_parser.c b/libavcodec/ mpegaudio_parser.cindex d54366f10a..d1a4ee6434 100644 --- a/libavcodec/mpegaudio_parser.c +++ b/libavcodec/mpegaudio_parser.c@@ -65,12 +65,12 @@ static int mpegaudio_parse(AVCodecParserContext *s1,} }else{ while(i<buf_size){ - int ret, sr, channels, bit_rate, frame_size;+ int ret, sr, channels, bit_rate, frame_size, dual_mono;enum AVCodecID codec_id = avctx->codec_id; state= (state<<8) + buf[i++];- ret = ff_mpa_decode_header(state, &sr, &channels, &frame_size, &bit_rate, &codec_id); + ret = ff_mpa_decode_header(state, &sr, &channels, &frame_size, &bit_rate, &codec_id, &dual_mono);if (ret < 4) { if (i > 4) s->header_count = -2; @@ -85,7 +85,13 @@ static int mpegaudio_parse(AVCodecParserContext *s1, if (s->header_count > header_threshold) { avctx->sample_rate= sr; av_channel_layout_uninit(&avctx->ch_layout);- av_channel_layout_default(&avctx- >ch_layout, channels);+ if (dual_mono) {+ av_channel_layout_custom_init(&avctx- >ch_layout, 2); + avctx->ch_layout.u.map[0].id = AV_CHAN_FRONT_CENTER; + avctx->ch_layout.u.map[1].id = AV_CHAN_FRONT_CENTER;Kind of sucks we have used FC to represent mono for so long that we can't cleanly introduce a new channel that's strictly mono (with no speaker location implied) and give it meaningful use.AV_CHAN_UNKNOWN?Using AV_CHAN_UNKNOWN would be fine with me.However, would using AV_CHANNEL_ORDER_UNSPEC instead of AV_CHANNEL_ORDER_CUSTOM be better?
UNSPEC means the channels have no definition. We could allow the user to assume 1 channel is "mono", but definitely not 2 channels for dual mono.
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