yading@10: /*
yading@10:  * Audio Mix Filter
yading@10:  * Copyright (c) 2012 Justin Ruggles <justin.ruggles@gmail.com>
yading@10:  *
yading@10:  * This file is part of Libav.
yading@10:  *
yading@10:  * Libav is free software; you can redistribute it and/or
yading@10:  * modify it under the terms of the GNU Lesser General Public
yading@10:  * License as published by the Free Software Foundation; either
yading@10:  * version 2.1 of the License, or (at your option) any later version.
yading@10:  *
yading@10:  * Libav is distributed in the hope that it will be useful,
yading@10:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
yading@10:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
yading@10:  * Lesser General Public License for more details.
yading@10:  *
yading@10:  * You should have received a copy of the GNU Lesser General Public
yading@10:  * License along with Libav; if not, write to the Free Software
yading@10:  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
yading@10:  */
yading@10: 
yading@10: /**
yading@10:  * @file
yading@10:  * Audio Mix Filter
yading@10:  *
yading@10:  * Mixes audio from multiple sources into a single output. The channel layout,
yading@10:  * sample rate, and sample format will be the same for all inputs and the
yading@10:  * output.
yading@10:  */
yading@10: 
yading@10: #include "libavutil/audio_fifo.h"
yading@10: #include "libavutil/avassert.h"
yading@10: #include "libavutil/avstring.h"
yading@10: #include "libavutil/channel_layout.h"
yading@10: #include "libavutil/common.h"
yading@10: #include "libavutil/float_dsp.h"
yading@10: #include "libavutil/mathematics.h"
yading@10: #include "libavutil/opt.h"
yading@10: #include "libavutil/samplefmt.h"
yading@10: 
yading@10: #include "audio.h"
yading@10: #include "avfilter.h"
yading@10: #include "formats.h"
yading@10: #include "internal.h"
yading@10: 
yading@10: #define INPUT_OFF      0    /**< input has reached EOF */
yading@10: #define INPUT_ON       1    /**< input is active */
yading@10: #define INPUT_INACTIVE 2    /**< input is on, but is currently inactive */
yading@10: 
yading@10: #define DURATION_LONGEST  0
yading@10: #define DURATION_SHORTEST 1
yading@10: #define DURATION_FIRST    2
yading@10: 
yading@10: 
yading@10: typedef struct FrameInfo {
yading@10:     int nb_samples;
yading@10:     int64_t pts;
yading@10:     struct FrameInfo *next;
yading@10: } FrameInfo;
yading@10: 
yading@10: /**
yading@10:  * Linked list used to store timestamps and frame sizes of all frames in the
yading@10:  * FIFO for the first input.
yading@10:  *
yading@10:  * This is needed to keep timestamps synchronized for the case where multiple
yading@10:  * input frames are pushed to the filter for processing before a frame is
yading@10:  * requested by the output link.
yading@10:  */
yading@10: typedef struct FrameList {
yading@10:     int nb_frames;
yading@10:     int nb_samples;
yading@10:     FrameInfo *list;
yading@10:     FrameInfo *end;
yading@10: } FrameList;
yading@10: 
yading@10: static void frame_list_clear(FrameList *frame_list)
yading@10: {
yading@10:     if (frame_list) {
yading@10:         while (frame_list->list) {
yading@10:             FrameInfo *info = frame_list->list;
yading@10:             frame_list->list = info->next;
yading@10:             av_free(info);
yading@10:         }
yading@10:         frame_list->nb_frames  = 0;
yading@10:         frame_list->nb_samples = 0;
yading@10:         frame_list->end        = NULL;
yading@10:     }
yading@10: }
yading@10: 
yading@10: static int frame_list_next_frame_size(FrameList *frame_list)
yading@10: {
yading@10:     if (!frame_list->list)
yading@10:         return 0;
yading@10:     return frame_list->list->nb_samples;
yading@10: }
yading@10: 
yading@10: static int64_t frame_list_next_pts(FrameList *frame_list)
yading@10: {
yading@10:     if (!frame_list->list)
yading@10:         return AV_NOPTS_VALUE;
yading@10:     return frame_list->list->pts;
yading@10: }
yading@10: 
yading@10: static void frame_list_remove_samples(FrameList *frame_list, int nb_samples)
yading@10: {
yading@10:     if (nb_samples >= frame_list->nb_samples) {
yading@10:         frame_list_clear(frame_list);
yading@10:     } else {
yading@10:         int samples = nb_samples;
yading@10:         while (samples > 0) {
yading@10:             FrameInfo *info = frame_list->list;
yading@10:             av_assert0(info != NULL);
yading@10:             if (info->nb_samples <= samples) {
yading@10:                 samples -= info->nb_samples;
yading@10:                 frame_list->list = info->next;
yading@10:                 if (!frame_list->list)
yading@10:                     frame_list->end = NULL;
yading@10:                 frame_list->nb_frames--;
yading@10:                 frame_list->nb_samples -= info->nb_samples;
yading@10:                 av_free(info);
yading@10:             } else {
yading@10:                 info->nb_samples       -= samples;
yading@10:                 info->pts              += samples;
yading@10:                 frame_list->nb_samples -= samples;
yading@10:                 samples = 0;
yading@10:             }
yading@10:         }
yading@10:     }
yading@10: }
yading@10: 
yading@10: static int frame_list_add_frame(FrameList *frame_list, int nb_samples, int64_t pts)
yading@10: {
yading@10:     FrameInfo *info = av_malloc(sizeof(*info));
yading@10:     if (!info)
yading@10:         return AVERROR(ENOMEM);
yading@10:     info->nb_samples = nb_samples;
yading@10:     info->pts        = pts;
yading@10:     info->next       = NULL;
yading@10: 
yading@10:     if (!frame_list->list) {
yading@10:         frame_list->list = info;
yading@10:         frame_list->end  = info;
yading@10:     } else {
yading@10:         av_assert0(frame_list->end != NULL);
yading@10:         frame_list->end->next = info;
yading@10:         frame_list->end       = info;
yading@10:     }
yading@10:     frame_list->nb_frames++;
yading@10:     frame_list->nb_samples += nb_samples;
yading@10: 
yading@10:     return 0;
yading@10: }
yading@10: 
yading@10: 
yading@10: typedef struct MixContext {
yading@10:     const AVClass *class;       /**< class for AVOptions */
yading@10:     AVFloatDSPContext fdsp;
yading@10: 
yading@10:     int nb_inputs;              /**< number of inputs */
yading@10:     int active_inputs;          /**< number of input currently active */
yading@10:     int duration_mode;          /**< mode for determining duration */
yading@10:     float dropout_transition;   /**< transition time when an input drops out */
yading@10: 
yading@10:     int nb_channels;            /**< number of channels */
yading@10:     int sample_rate;            /**< sample rate */
yading@10:     int planar;
yading@10:     AVAudioFifo **fifos;        /**< audio fifo for each input */
yading@10:     uint8_t *input_state;       /**< current state of each input */
yading@10:     float *input_scale;         /**< mixing scale factor for each input */
yading@10:     float scale_norm;           /**< normalization factor for all inputs */
yading@10:     int64_t next_pts;           /**< calculated pts for next output frame */
yading@10:     FrameList *frame_list;      /**< list of frame info for the first input */
yading@10: } MixContext;
yading@10: 
yading@10: #define OFFSET(x) offsetof(MixContext, x)
yading@10: #define A AV_OPT_FLAG_AUDIO_PARAM
yading@10: #define F AV_OPT_FLAG_FILTERING_PARAM
yading@10: static const AVOption amix_options[] = {
yading@10:     { "inputs", "Number of inputs.",
yading@10:             OFFSET(nb_inputs), AV_OPT_TYPE_INT, { .i64 = 2 }, 1, 32, A|F },
yading@10:     { "duration", "How to determine the end-of-stream.",
yading@10:             OFFSET(duration_mode), AV_OPT_TYPE_INT, { .i64 = DURATION_LONGEST }, 0,  2, A|F, "duration" },
yading@10:         { "longest",  "Duration of longest input.",  0, AV_OPT_TYPE_CONST, { .i64 = DURATION_LONGEST  }, INT_MIN, INT_MAX, A|F, "duration" },
yading@10:         { "shortest", "Duration of shortest input.", 0, AV_OPT_TYPE_CONST, { .i64 = DURATION_SHORTEST }, INT_MIN, INT_MAX, A|F, "duration" },
yading@10:         { "first",    "Duration of first input.",    0, AV_OPT_TYPE_CONST, { .i64 = DURATION_FIRST    }, INT_MIN, INT_MAX, A|F, "duration" },
yading@10:     { "dropout_transition", "Transition time, in seconds, for volume "
yading@10:                             "renormalization when an input stream ends.",
yading@10:             OFFSET(dropout_transition), AV_OPT_TYPE_FLOAT, { .dbl = 2.0 }, 0, INT_MAX, A|F },
yading@10:     { NULL },
yading@10: };
yading@10: 
yading@10: AVFILTER_DEFINE_CLASS(amix);
yading@10: 
yading@10: /**
yading@10:  * Update the scaling factors to apply to each input during mixing.
yading@10:  *
yading@10:  * This balances the full volume range between active inputs and handles
yading@10:  * volume transitions when EOF is encountered on an input but mixing continues
yading@10:  * with the remaining inputs.
yading@10:  */
yading@10: static void calculate_scales(MixContext *s, int nb_samples)
yading@10: {
yading@10:     int i;
yading@10: 
yading@10:     if (s->scale_norm > s->active_inputs) {
yading@10:         s->scale_norm -= nb_samples / (s->dropout_transition * s->sample_rate);
yading@10:         s->scale_norm = FFMAX(s->scale_norm, s->active_inputs);
yading@10:     }
yading@10: 
yading@10:     for (i = 0; i < s->nb_inputs; i++) {
yading@10:         if (s->input_state[i] == INPUT_ON)
yading@10:             s->input_scale[i] = 1.0f / s->scale_norm;
yading@10:         else
yading@10:             s->input_scale[i] = 0.0f;
yading@10:     }
yading@10: }
yading@10: 
yading@10: static int config_output(AVFilterLink *outlink)
yading@10: {
yading@10:     AVFilterContext *ctx = outlink->src;
yading@10:     MixContext *s      = ctx->priv;
yading@10:     int i;
yading@10:     char buf[64];
yading@10: 
yading@10:     s->planar          = av_sample_fmt_is_planar(outlink->format);
yading@10:     s->sample_rate     = outlink->sample_rate;
yading@10:     outlink->time_base = (AVRational){ 1, outlink->sample_rate };
yading@10:     s->next_pts        = AV_NOPTS_VALUE;
yading@10: 
yading@10:     s->frame_list = av_mallocz(sizeof(*s->frame_list));
yading@10:     if (!s->frame_list)
yading@10:         return AVERROR(ENOMEM);
yading@10: 
yading@10:     s->fifos = av_mallocz(s->nb_inputs * sizeof(*s->fifos));
yading@10:     if (!s->fifos)
yading@10:         return AVERROR(ENOMEM);
yading@10: 
yading@10:     s->nb_channels = av_get_channel_layout_nb_channels(outlink->channel_layout);
yading@10:     for (i = 0; i < s->nb_inputs; i++) {
yading@10:         s->fifos[i] = av_audio_fifo_alloc(outlink->format, s->nb_channels, 1024);
yading@10:         if (!s->fifos[i])
yading@10:             return AVERROR(ENOMEM);
yading@10:     }
yading@10: 
yading@10:     s->input_state = av_malloc(s->nb_inputs);
yading@10:     if (!s->input_state)
yading@10:         return AVERROR(ENOMEM);
yading@10:     memset(s->input_state, INPUT_ON, s->nb_inputs);
yading@10:     s->active_inputs = s->nb_inputs;
yading@10: 
yading@10:     s->input_scale = av_mallocz(s->nb_inputs * sizeof(*s->input_scale));
yading@10:     if (!s->input_scale)
yading@10:         return AVERROR(ENOMEM);
yading@10:     s->scale_norm = s->active_inputs;
yading@10:     calculate_scales(s, 0);
yading@10: 
yading@10:     av_get_channel_layout_string(buf, sizeof(buf), -1, outlink->channel_layout);
yading@10: 
yading@10:     av_log(ctx, AV_LOG_VERBOSE,
yading@10:            "inputs:%d fmt:%s srate:%d cl:%s\n", s->nb_inputs,
yading@10:            av_get_sample_fmt_name(outlink->format), outlink->sample_rate, buf);
yading@10: 
yading@10:     return 0;
yading@10: }
yading@10: 
yading@10: /**
yading@10:  * Read samples from the input FIFOs, mix, and write to the output link.
yading@10:  */
yading@10: static int output_frame(AVFilterLink *outlink, int nb_samples)
yading@10: {
yading@10:     AVFilterContext *ctx = outlink->src;
yading@10:     MixContext      *s = ctx->priv;
yading@10:     AVFrame *out_buf, *in_buf;
yading@10:     int i;
yading@10: 
yading@10:     calculate_scales(s, nb_samples);
yading@10: 
yading@10:     out_buf = ff_get_audio_buffer(outlink, nb_samples);
yading@10:     if (!out_buf)
yading@10:         return AVERROR(ENOMEM);
yading@10: 
yading@10:     in_buf = ff_get_audio_buffer(outlink, nb_samples);
yading@10:     if (!in_buf) {
yading@10:         av_frame_free(&out_buf);
yading@10:         return AVERROR(ENOMEM);
yading@10:     }
yading@10: 
yading@10:     for (i = 0; i < s->nb_inputs; i++) {
yading@10:         if (s->input_state[i] == INPUT_ON) {
yading@10:             int planes, plane_size, p;
yading@10: 
yading@10:             av_audio_fifo_read(s->fifos[i], (void **)in_buf->extended_data,
yading@10:                                nb_samples);
yading@10: 
yading@10:             planes     = s->planar ? s->nb_channels : 1;
yading@10:             plane_size = nb_samples * (s->planar ? 1 : s->nb_channels);
yading@10:             plane_size = FFALIGN(plane_size, 16);
yading@10: 
yading@10:             for (p = 0; p < planes; p++) {
yading@10:                 s->fdsp.vector_fmac_scalar((float *)out_buf->extended_data[p],
yading@10:                                            (float *) in_buf->extended_data[p],
yading@10:                                            s->input_scale[i], plane_size);
yading@10:             }
yading@10:         }
yading@10:     }
yading@10:     av_frame_free(&in_buf);
yading@10: 
yading@10:     out_buf->pts = s->next_pts;
yading@10:     if (s->next_pts != AV_NOPTS_VALUE)
yading@10:         s->next_pts += nb_samples;
yading@10: 
yading@10:     return ff_filter_frame(outlink, out_buf);
yading@10: }
yading@10: 
yading@10: /**
yading@10:  * Returns the smallest number of samples available in the input FIFOs other
yading@10:  * than that of the first input.
yading@10:  */
yading@10: static int get_available_samples(MixContext *s)
yading@10: {
yading@10:     int i;
yading@10:     int available_samples = INT_MAX;
yading@10: 
yading@10:     av_assert0(s->nb_inputs > 1);
yading@10: 
yading@10:     for (i = 1; i < s->nb_inputs; i++) {
yading@10:         int nb_samples;
yading@10:         if (s->input_state[i] == INPUT_OFF)
yading@10:             continue;
yading@10:         nb_samples = av_audio_fifo_size(s->fifos[i]);
yading@10:         available_samples = FFMIN(available_samples, nb_samples);
yading@10:     }
yading@10:     if (available_samples == INT_MAX)
yading@10:         return 0;
yading@10:     return available_samples;
yading@10: }
yading@10: 
yading@10: /**
yading@10:  * Requests a frame, if needed, from each input link other than the first.
yading@10:  */
yading@10: static int request_samples(AVFilterContext *ctx, int min_samples)
yading@10: {
yading@10:     MixContext *s = ctx->priv;
yading@10:     int i, ret;
yading@10: 
yading@10:     av_assert0(s->nb_inputs > 1);
yading@10: 
yading@10:     for (i = 1; i < s->nb_inputs; i++) {
yading@10:         ret = 0;
yading@10:         if (s->input_state[i] == INPUT_OFF)
yading@10:             continue;
yading@10:         while (!ret && av_audio_fifo_size(s->fifos[i]) < min_samples)
yading@10:             ret = ff_request_frame(ctx->inputs[i]);
yading@10:         if (ret == AVERROR_EOF) {
yading@10:             if (av_audio_fifo_size(s->fifos[i]) == 0) {
yading@10:                 s->input_state[i] = INPUT_OFF;
yading@10:                 continue;
yading@10:             }
yading@10:         } else if (ret < 0)
yading@10:             return ret;
yading@10:     }
yading@10:     return 0;
yading@10: }
yading@10: 
yading@10: /**
yading@10:  * Calculates the number of active inputs and determines EOF based on the
yading@10:  * duration option.
yading@10:  *
yading@10:  * @return 0 if mixing should continue, or AVERROR_EOF if mixing should stop.
yading@10:  */
yading@10: static int calc_active_inputs(MixContext *s)
yading@10: {
yading@10:     int i;
yading@10:     int active_inputs = 0;
yading@10:     for (i = 0; i < s->nb_inputs; i++)
yading@10:         active_inputs += !!(s->input_state[i] != INPUT_OFF);
yading@10:     s->active_inputs = active_inputs;
yading@10: 
yading@10:     if (!active_inputs ||
yading@10:         (s->duration_mode == DURATION_FIRST && s->input_state[0] == INPUT_OFF) ||
yading@10:         (s->duration_mode == DURATION_SHORTEST && active_inputs != s->nb_inputs))
yading@10:         return AVERROR_EOF;
yading@10:     return 0;
yading@10: }
yading@10: 
yading@10: static int request_frame(AVFilterLink *outlink)
yading@10: {
yading@10:     AVFilterContext *ctx = outlink->src;
yading@10:     MixContext      *s = ctx->priv;
yading@10:     int ret;
yading@10:     int wanted_samples, available_samples;
yading@10: 
yading@10:     ret = calc_active_inputs(s);
yading@10:     if (ret < 0)
yading@10:         return ret;
yading@10: 
yading@10:     if (s->input_state[0] == INPUT_OFF) {
yading@10:         ret = request_samples(ctx, 1);
yading@10:         if (ret < 0)
yading@10:             return ret;
yading@10: 
yading@10:         ret = calc_active_inputs(s);
yading@10:         if (ret < 0)
yading@10:             return ret;
yading@10: 
yading@10:         available_samples = get_available_samples(s);
yading@10:         if (!available_samples)
yading@10:             return AVERROR(EAGAIN);
yading@10: 
yading@10:         return output_frame(outlink, available_samples);
yading@10:     }
yading@10: 
yading@10:     if (s->frame_list->nb_frames == 0) {
yading@10:         ret = ff_request_frame(ctx->inputs[0]);
yading@10:         if (ret == AVERROR_EOF) {
yading@10:             s->input_state[0] = INPUT_OFF;
yading@10:             if (s->nb_inputs == 1)
yading@10:                 return AVERROR_EOF;
yading@10:             else
yading@10:                 return AVERROR(EAGAIN);
yading@10:         } else if (ret < 0)
yading@10:             return ret;
yading@10:     }
yading@10:     av_assert0(s->frame_list->nb_frames > 0);
yading@10: 
yading@10:     wanted_samples = frame_list_next_frame_size(s->frame_list);
yading@10: 
yading@10:     if (s->active_inputs > 1) {
yading@10:         ret = request_samples(ctx, wanted_samples);
yading@10:         if (ret < 0)
yading@10:             return ret;
yading@10: 
yading@10:         ret = calc_active_inputs(s);
yading@10:         if (ret < 0)
yading@10:             return ret;
yading@10:     }
yading@10: 
yading@10:     if (s->active_inputs > 1) {
yading@10:         available_samples = get_available_samples(s);
yading@10:         if (!available_samples)
yading@10:             return AVERROR(EAGAIN);
yading@10:         available_samples = FFMIN(available_samples, wanted_samples);
yading@10:     } else {
yading@10:         available_samples = wanted_samples;
yading@10:     }
yading@10: 
yading@10:     s->next_pts = frame_list_next_pts(s->frame_list);
yading@10:     frame_list_remove_samples(s->frame_list, available_samples);
yading@10: 
yading@10:     return output_frame(outlink, available_samples);
yading@10: }
yading@10: 
yading@10: static int filter_frame(AVFilterLink *inlink, AVFrame *buf)
yading@10: {
yading@10:     AVFilterContext  *ctx = inlink->dst;
yading@10:     MixContext       *s = ctx->priv;
yading@10:     AVFilterLink *outlink = ctx->outputs[0];
yading@10:     int i, ret = 0;
yading@10: 
yading@10:     for (i = 0; i < ctx->nb_inputs; i++)
yading@10:         if (ctx->inputs[i] == inlink)
yading@10:             break;
yading@10:     if (i >= ctx->nb_inputs) {
yading@10:         av_log(ctx, AV_LOG_ERROR, "unknown input link\n");
yading@10:         ret = AVERROR(EINVAL);
yading@10:         goto fail;
yading@10:     }
yading@10: 
yading@10:     if (i == 0) {
yading@10:         int64_t pts = av_rescale_q(buf->pts, inlink->time_base,
yading@10:                                    outlink->time_base);
yading@10:         ret = frame_list_add_frame(s->frame_list, buf->nb_samples, pts);
yading@10:         if (ret < 0)
yading@10:             goto fail;
yading@10:     }
yading@10: 
yading@10:     ret = av_audio_fifo_write(s->fifos[i], (void **)buf->extended_data,
yading@10:                               buf->nb_samples);
yading@10: 
yading@10: fail:
yading@10:     av_frame_free(&buf);
yading@10: 
yading@10:     return ret;
yading@10: }
yading@10: 
yading@10: static int init(AVFilterContext *ctx)
yading@10: {
yading@10:     MixContext *s = ctx->priv;
yading@10:     int i;
yading@10: 
yading@10:     for (i = 0; i < s->nb_inputs; i++) {
yading@10:         char name[32];
yading@10:         AVFilterPad pad = { 0 };
yading@10: 
yading@10:         snprintf(name, sizeof(name), "input%d", i);
yading@10:         pad.type           = AVMEDIA_TYPE_AUDIO;
yading@10:         pad.name           = av_strdup(name);
yading@10:         pad.filter_frame   = filter_frame;
yading@10: 
yading@10:         ff_insert_inpad(ctx, i, &pad);
yading@10:     }
yading@10: 
yading@10:     avpriv_float_dsp_init(&s->fdsp, 0);
yading@10: 
yading@10:     return 0;
yading@10: }
yading@10: 
yading@10: static void uninit(AVFilterContext *ctx)
yading@10: {
yading@10:     int i;
yading@10:     MixContext *s = ctx->priv;
yading@10: 
yading@10:     if (s->fifos) {
yading@10:         for (i = 0; i < s->nb_inputs; i++)
yading@10:             av_audio_fifo_free(s->fifos[i]);
yading@10:         av_freep(&s->fifos);
yading@10:     }
yading@10:     frame_list_clear(s->frame_list);
yading@10:     av_freep(&s->frame_list);
yading@10:     av_freep(&s->input_state);
yading@10:     av_freep(&s->input_scale);
yading@10: 
yading@10:     for (i = 0; i < ctx->nb_inputs; i++)
yading@10:         av_freep(&ctx->input_pads[i].name);
yading@10: }
yading@10: 
yading@10: static int query_formats(AVFilterContext *ctx)
yading@10: {
yading@10:     AVFilterFormats *formats = NULL;
yading@10:     ff_add_format(&formats, AV_SAMPLE_FMT_FLT);
yading@10:     ff_add_format(&formats, AV_SAMPLE_FMT_FLTP);
yading@10:     ff_set_common_formats(ctx, formats);
yading@10:     ff_set_common_channel_layouts(ctx, ff_all_channel_layouts());
yading@10:     ff_set_common_samplerates(ctx, ff_all_samplerates());
yading@10:     return 0;
yading@10: }
yading@10: 
yading@10: static const AVFilterPad avfilter_af_amix_outputs[] = {
yading@10:     {
yading@10:         .name          = "default",
yading@10:         .type          = AVMEDIA_TYPE_AUDIO,
yading@10:         .config_props  = config_output,
yading@10:         .request_frame = request_frame
yading@10:     },
yading@10:     { NULL }
yading@10: };
yading@10: 
yading@10: AVFilter avfilter_af_amix = {
yading@10:     .name          = "amix",
yading@10:     .description   = NULL_IF_CONFIG_SMALL("Audio mixing."),
yading@10:     .priv_size     = sizeof(MixContext),
yading@10:     .priv_class    = &amix_class,
yading@10: 
yading@10:     .init           = init,
yading@10:     .uninit         = uninit,
yading@10:     .query_formats  = query_formats,
yading@10: 
yading@10:     .inputs    = NULL,
yading@10:     .outputs   = avfilter_af_amix_outputs,
yading@10: 
yading@10:     .flags     = AVFILTER_FLAG_DYNAMIC_INPUTS,
yading@10: };