[FFmpeg-devel] [PATCH] avfilter/af_channelsplit: add channels option
Nicolas George
george at nsup.org
Wed Mar 21 18:48:28 EET 2018
Paul B Mahol (2018-03-20):
> So user can pick which channels to extract.
>
> Signed-off-by: Paul B Mahol <onemda at gmail.com>
> ---
> doc/filters.texi | 15 ++++++++++++
> libavfilter/af_channelsplit.c | 54 +++++++++++++++++++++++++++++++++++--------
> 2 files changed, 60 insertions(+), 9 deletions(-)
Quick and incomplete review, for the sake of courtesy.
>
> diff --git a/doc/filters.texi b/doc/filters.texi
> index bd43a7ac6e..81310e1cdf 100644
> --- a/doc/filters.texi
> +++ b/doc/filters.texi
> @@ -2208,8 +2208,14 @@ It accepts the following parameters:
> @table @option
> @item channel_layout
> The channel layout of the input stream. The default is "stereo".
> + at item channels
> +The channel layout of the channels for extraction. The default is "all".
You do not specify what happens if it specifies channels that are not
present in the input.
> @end table
>
> + at subsection Examples
> +
> + at itemize
> + at item
> For example, assuming a stereo input MP3 file,
> @example
> ffmpeg -i in.mp3 -filter_complex channelsplit out.mkv
> @@ -2217,6 +2223,7 @@ ffmpeg -i in.mp3 -filter_complex channelsplit out.mkv
> will create an output Matroska file with two audio streams, one containing only
> the left channel and the other the right channel.
>
> + at item
> Split a 5.1 WAV file into per-channel files:
> @example
> ffmpeg -i in.wav -filter_complex
> @@ -2226,6 +2233,14 @@ front_center.wav -map '[LFE]' lfe.wav -map '[SL]' side_left.wav -map '[SR]'
> side_right.wav
> @end example
>
> + at item
> +Extract LFE from a 5.1 WAV file:
> + at example
> +ffmpeg -i in.wav -filter_complex 'channelsplit=channel_layout=5.1:LFE[LFE]'
"channel_layout=5.1:channels=LFE"; avoid giving examples relying on
the order of options, especially for secondary ones.
> +-map '[LFE]' lfe.wav
> + at end example
> + at end itemize
> +
> @section chorus
> Add a chorus effect to the audio.
>
> diff --git a/libavfilter/af_channelsplit.c b/libavfilter/af_channelsplit.c
> index 8c6b00fe4f..d9b9a60420 100644
> --- a/libavfilter/af_channelsplit.c
> +++ b/libavfilter/af_channelsplit.c
> @@ -38,6 +38,9 @@ typedef struct ChannelSplitContext {
>
> uint64_t channel_layout;
> char *channel_layout_str;
> + char *channels_str;
> +
> + int map[64];
Minor: could be char to save some memory.
> } ChannelSplitContext;
>
> #define OFFSET(x) offsetof(ChannelSplitContext, x)
> @@ -45,6 +48,7 @@ typedef struct ChannelSplitContext {
> #define F AV_OPT_FLAG_FILTERING_PARAM
> static const AVOption channelsplit_options[] = {
> { "channel_layout", "Input channel layout.", OFFSET(channel_layout_str), AV_OPT_TYPE_STRING, { .str = "stereo" }, .flags = A|F },
> + { "channels", "Channels to extract.", OFFSET(channels_str), AV_OPT_TYPE_STRING, { .str = "all" }, .flags = A|F },
> { NULL }
> };
>
> @@ -64,15 +68,46 @@ static av_cold int init(AVFilterContext *ctx)
> }
>
> nb_channels = av_get_channel_layout_nb_channels(s->channel_layout);
> - for (i = 0; i < nb_channels; i++) {
> - uint64_t channel = av_channel_layout_extract_channel(s->channel_layout, i);
> - AVFilterPad pad = { 0 };
>
> - pad.type = AVMEDIA_TYPE_AUDIO;
> - pad.name = av_get_channel_name(channel);
> + if (!strcmp(s->channels_str, "all")) {
> + for (i = 0; i < nb_channels; i++) {
> + uint64_t channel = av_channel_layout_extract_channel(s->channel_layout, i);
> + AVFilterPad pad = { 0 };
> +
> + pad.type = AVMEDIA_TYPE_AUDIO;
> + pad.name = av_get_channel_name(channel);
> +
> + s->map[i] = i;
>
> - if ((ret = ff_insert_outpad(ctx, i, &pad)) < 0) {
> + if ((ret = ff_insert_outpad(ctx, i, &pad)) < 0) {
> + return ret;
> + }
> + }
> + } else {
> + uint64_t channel_layout;
> + int nb_extracted_channels;
Inconsistent variable names.
> +
> + if ((ret = av_get_extended_channel_layout(s->channels_str, &channel_layout, &nb_extracted_channels)) < 0)
> return ret;
> +
> + for (i = 0; i < nb_extracted_channels; i++) {
> + uint64_t channel = av_channel_layout_extract_channel(channel_layout, i);
> + AVFilterPad pad = { 0 };
> +
> + if ((ret = av_get_channel_layout_channel_index(s->channel_layout, channel)) < 0) {
> + av_log(ctx, AV_LOG_ERROR, "Channel name '%s' not present in channel layout '%s'.\n",
> + av_get_channel_name(channel), s->channel_layout_str);
> + return ret;
> + }
> +
> + s->map[i] = ret;
> +
> + pad.type = AVMEDIA_TYPE_AUDIO;
> + pad.name = av_get_channel_name(channel);
> +
> + if ((ret = ff_insert_outpad(ctx, i, &pad)) < 0) {
> + return ret;
> + }
Stop using copy-paste! Set extracted_channels to either the parsed value
or the same as s->channel_layout and build the map only once.
> }
> }
>
> @@ -96,7 +131,7 @@ static int query_formats(AVFilterContext *ctx)
>
> for (i = 0; i < ctx->nb_outputs; i++) {
> AVFilterChannelLayouts *out_layouts = NULL;
> - uint64_t channel = av_channel_layout_extract_channel(s->channel_layout, i);
> + uint64_t channel = av_channel_layout_extract_channel(s->channel_layout, s->map[i]);
>
> if ((ret = ff_add_channel_layout(&out_layouts, channel)) < 0 ||
> (ret = ff_channel_layouts_ref(out_layouts, &ctx->outputs[i]->in_channel_layouts)) < 0)
> @@ -109,6 +144,7 @@ static int query_formats(AVFilterContext *ctx)
> static int filter_frame(AVFilterLink *inlink, AVFrame *buf)
> {
> AVFilterContext *ctx = inlink->dst;
> + ChannelSplitContext *s = ctx->priv;
> int i, ret = 0;
>
> for (i = 0; i < ctx->nb_outputs; i++) {
> @@ -119,9 +155,9 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *buf)
> break;
> }
>
> - buf_out->data[0] = buf_out->extended_data[0] = buf_out->extended_data[i];
> + buf_out->data[0] = buf_out->extended_data[0] = buf_out->extended_data[s->map[i]];
> buf_out->channel_layout =
> - av_channel_layout_extract_channel(buf->channel_layout, i);
> + av_channel_layout_extract_channel(buf->channel_layout, s->map[i]);
> buf_out->channels = 1;
>
> ret = ff_filter_frame(ctx->outputs[i], buf_out);
Regards,
--
Nicolas George
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