af_lavfi: add libavfilter bridge

Mostly copied from vf_lavfi. The parts that could be shared are minor,
because most code is about setting up audio and video, which are too
different.

This won't work with Libav. I used ffplay.c as guide, and noticed too
late that their setup methods are incompatible with Libav's. Trying to
make it work with both would be too much effort. The configure test for
av_opt_set_int_list() should disable af_lavfi gracefully when compiling
with Libav.

Due to option parser chaos, you currently can't have a "," as part of
the filter graph string - not even with quoting or escaping. This will
probably be fixed later.

The audio filter chain is not PTS aware. So we have to do some hacks
to make up a fake PTS, and we have to map the output PTS back to the
filter chain's method of tracking PTS changes and buffering, by
adjusting af->delay.

DOCS/man/en/af.rst

@@ -550,3 +550,13 @@ scaletempo[=option1:option2:...]
         Would playback audio file at 1.2x normal speed, with audio at normal
         pitch. Changing playback speed, would change pitch, leaving audio
         tempo at 1.2x.
+
+lavfi=graph
+    Filter audio using ffmpeg's libavfilter.
+
+    <graph>
+        Libavfilter graph. See ``lavfi`` video filter for details - the graph
+        syntax is the same.
+
+        Warning: due to shortcomings in the current ``-af`` option parser code,
+        the filter graph must not contain any ``,``.

Makefile

@@ -118,6 +118,7 @@ SOURCES-$(X11)                  += video/out/vo_x11.c video/out/x11_common.c
 SOURCES-$(XV)                   += video/out/vo_xv.c
 
 SOURCES-$(VF_LAVFI)             += video/filter/vf_lavfi.c
+SOURCES-$(AF_LAVFI)             += audio/filter/af_lavfi.c
 
 ifeq ($(HAVE_AVUTIL_REFCOUNTING),no)
     SOURCES-yes                 += video/decode/lavc_dr1.c

audio/filter/af.c

@@ -48,6 +48,7 @@ extern struct af_info af_info_sinesuppress;
 extern struct af_info af_info_karaoke;
 extern struct af_info af_info_scaletempo;
 extern struct af_info af_info_bs2b;
+extern struct af_info af_info_lavfi;
 
 static struct af_info* filter_list[] = {
     &af_info_dummy,
@@ -77,6 +78,9 @@ static struct af_info* filter_list[] = {
     &af_info_scaletempo,
 #ifdef CONFIG_LIBBS2B
     &af_info_bs2b,
+#endif
+#ifdef CONFIG_AF_LAVFI
+    &af_info_lavfi,
 #endif
     // Must come last, because it's the fallback format conversion filter
     &af_info_format,

audio/filter/af_lavfi.c

@@ -0,0 +1,306 @@
+/*
+ * This file is part of mpv.
+ *
+ * Filter graph creation code taken from FFmpeg ffplay.c (LGPL 2.1 or later)
+ *
+ * mpv is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * mpv is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with mpv.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <assert.h>
+
+#include <libavutil/avstring.h>
+#include <libavutil/mem.h>
+#include <libavutil/mathematics.h>
+#include <libavutil/rational.h>
+#include <libavutil/samplefmt.h>
+#include <libavutil/time.h>
+#include <libavutil/opt.h>
+#include <libavfilter/avfilter.h>
+#include <libavfilter/avfiltergraph.h>
+#include <libavfilter/buffersink.h>
+#include <libavfilter/buffersrc.h>
+
+#include "audio/format.h"
+#include "audio/fmt-conversion.h"
+#include "af.h"
+
+#define IS_LIBAV_FORK (LIBAVFILTER_VERSION_MICRO < 100)
+
+// FFmpeg and Libav have slightly different APIs, just enough to cause us
+// unnecessary pain. <Expletive deleted.>
+#if IS_LIBAV_FORK
+#define graph_parse(graph, filters, inputs, outputs, log_ctx) \
+    avfilter_graph_parse(graph, filters, inputs, outputs, log_ctx)
+#else
+#define graph_parse(graph, filters, inputs, outputs, log_ctx) \
+    avfilter_graph_parse(graph, filters, &(inputs), &(outputs), log_ctx)
+#endif
+
+struct priv {
+    AVFilterGraph *graph;
+    AVFilterContext *in;
+    AVFilterContext *out;
+
+    // Guarantee that the data stays valid until next filter call
+    char *out_buffer;
+
+    struct mp_audio data;
+    struct mp_audio temp;
+
+    int64_t bytes_in;
+    int64_t bytes_out;
+
+    AVRational timebase_out;
+
+    // options
+    char *cfg_graph;
+};
+
+static void destroy_graph(struct af_instance *af)
+{
+    struct priv *p = af->setup;
+    avfilter_graph_free(&p->graph);
+    p->in = p->out = NULL;
+}
+
+static bool recreate_graph(struct af_instance *af, struct mp_audio *config)
+{
+    void *tmp = talloc_new(NULL);
+    struct priv *p = af->setup;
+    AVFilterContext *in = NULL, *out = NULL;
+    int r;
+
+    if (bstr0(p->cfg_graph).len == 0) {
+        mp_msg(MSGT_AFILTER, MSGL_FATAL, "lavfi: no filter graph set\n");
+        return false;
+    }
+
+    destroy_graph(af);
+    mp_msg(MSGT_AFILTER, MSGL_V, "lavfi: create graph: '%s'\n", p->cfg_graph);
+
+    AVFilterGraph *graph = avfilter_graph_alloc();
+    if (!graph)
+        goto error;
+
+    AVFilterInOut *outputs = avfilter_inout_alloc();
+    AVFilterInOut *inputs  = avfilter_inout_alloc();
+    if (!outputs || !inputs)
+        goto error;
+
+    char *src_args = talloc_asprintf(tmp,
+        "sample_rate=%d:sample_fmt=%s:channels=%d:time_base=%d/%d:"
+        "channel_layout=0x%"PRIx64,  config->rate,
+        av_get_sample_fmt_name(af_to_avformat(config->format)),
+        config->channels.num, 1, config->rate,
+        mp_chmap_to_lavc(&config->channels));
+
+    if (avfilter_graph_create_filter(&in, avfilter_get_by_name("abuffer"),
+                                     "src", src_args, NULL, graph) < 0)
+        goto error;
+
+    if (avfilter_graph_create_filter(&out, avfilter_get_by_name("abuffersink"),
+                                     "out", NULL, NULL, graph) < 0)
+        goto error;
+
+    static const enum AVSampleFormat sample_fmts[] = {
+        AV_SAMPLE_FMT_U8, AV_SAMPLE_FMT_S16, AV_SAMPLE_FMT_S32,
+        AV_SAMPLE_FMT_FLT, AV_SAMPLE_FMT_DBL,
+        AV_SAMPLE_FMT_NONE
+    };
+    r = av_opt_set_int_list(out, "sample_fmts", sample_fmts,
+                            AV_SAMPLE_FMT_NONE, AV_OPT_SEARCH_CHILDREN);
+    if (r < 0)
+        goto error;
+
+    r = av_opt_set_int(out, "all_channel_counts", 1, AV_OPT_SEARCH_CHILDREN);
+    if (r < 0)
+        goto error;
+
+    outputs->name = av_strdup("in");
+    outputs->filter_ctx = in;
+
+    inputs->name = av_strdup("out");
+    inputs->filter_ctx = out;
+
+    if (graph_parse(graph, p->cfg_graph, inputs, outputs, NULL) < 0)
+        goto error;
+
+    if (avfilter_graph_config(graph, NULL) < 0)
+        goto error;
+
+    p->in = in;
+    p->out = out;
+    p->graph = graph;
+
+    assert(out->nb_inputs == 1);
+    assert(in->nb_outputs == 1);
+
+    talloc_free(tmp);
+    return true;
+
+error:
+    mp_msg(MSGT_AFILTER, MSGL_FATAL, "Can't configure libavfilter graph.\n");
+    avfilter_graph_free(&graph);
+    talloc_free(tmp);
+    return false;
+}
+
+static int control(struct af_instance *af, int cmd, void *arg)
+{
+    struct priv *p = af->setup;
+
+    switch (cmd) {
+    case AF_CONTROL_REINIT: {
+        struct mp_audio *in = arg;
+        struct mp_audio orig_in = *in;
+        struct mp_audio *out = af->data;
+
+        if (af_to_avformat(in->format) == AV_SAMPLE_FMT_NONE)
+            mp_audio_set_format(in, AF_FORMAT_FLOAT_NE);
+
+        if (!mp_chmap_is_lavc(&in->channels))
+            mp_chmap_reorder_to_lavc(&in->channels); // will always work
+
+        if (!recreate_graph(af, in))
+            return AF_ERROR;
+
+        AVFilterLink *l_out = p->out->inputs[0];
+
+        out->rate = l_out->sample_rate;
+
+        mp_audio_set_format(out, af_from_avformat(l_out->format));
+
+        struct mp_chmap out_cm;
+        mp_chmap_from_lavc(&out_cm, l_out->channel_layout);
+        if (!out_cm.num || out_cm.num != l_out->channels)
+            mp_chmap_from_channels(&out_cm, l_out->channels);
+        mp_audio_set_channels(out, &out_cm);
+
+        p->timebase_out = l_out->time_base;
+
+        af->mul = (double) (out->rate * out->nch) / (in->rate * in->nch);
+
+        return mp_audio_config_equals(in, &orig_in) ? AF_OK : AF_FALSE;
+    }
+    case AF_CONTROL_COMMAND_LINE: {
+        talloc_free(p->cfg_graph);
+        p->cfg_graph = talloc_strdup(p, (char *)arg);
+        return AF_OK;
+    }
+    }
+    return AF_UNKNOWN;
+}
+
+static struct mp_audio *play(struct af_instance *af, struct mp_audio *data)
+{
+    struct priv *p = af->setup;
+
+    AVFilterLink *l_in = p->in->outputs[0];
+
+    struct mp_audio *r = &p->temp;
+    *r = *af->data;
+
+    int in_frame_size = data->bps * data->channels.num;
+    int out_frame_size = r->bps * r->channels.num;
+
+    AVFrame *frame = av_frame_alloc();
+    frame->nb_samples = data->len / in_frame_size;
+    frame->format = l_in->format;
+
+    // Timebase is 1/sample_rate
+    frame->pts = p->bytes_in / in_frame_size;
+
+    av_frame_set_channels(frame, l_in->channels);
+    av_frame_set_channel_layout(frame, l_in->channel_layout);
+    av_frame_set_sample_rate(frame, l_in->sample_rate);
+
+    frame->data[0] = data->audio;
+    frame->extended_data = frame->data;
+
+    if (av_buffersrc_add_frame(p->in, frame) < 0) {
+        av_frame_free(&frame);
+        return NULL;
+    }
+    av_frame_free(&frame);
+
+    int64_t out_pts = AV_NOPTS_VALUE;
+    size_t out_len = 0;
+    for (;;) {
+        frame = av_frame_alloc();
+        if (av_buffersink_get_frame(p->out, frame) < 0) {
+            // Not an error situation - no more output buffers in queue.
+            av_frame_free(&frame);
+            break;
+        }
+
+        size_t new_len = out_len + frame->nb_samples * out_frame_size;
+        if (new_len > talloc_get_size(p->out_buffer))
+            p->out_buffer = talloc_realloc(p, p->out_buffer, char, new_len);
+        memcpy(p->out_buffer + out_len, frame->data[0], new_len - out_len);
+        out_len = new_len;
+        if (out_pts == AV_NOPTS_VALUE)
+            out_pts = frame->pts;
+
+        av_frame_free(&frame);
+    }
+
+    r->audio = p->out_buffer;
+    r->len = out_len;
+
+    p->bytes_in += data->len;
+    p->bytes_out += r->len;
+
+    if (out_pts != AV_NOPTS_VALUE) {
+        int64_t num_in_frames = p->bytes_in / in_frame_size;
+        double in_time = num_in_frames / (double)data->rate;
+
+        double out_time = out_pts * av_q2d(p->timebase_out);
+        // Need pts past the last output sample.
+        int out_frames = r->len / out_frame_size;
+        out_time += out_frames / (double)r->rate;
+
+        af->delay = (in_time - out_time) * r->rate * out_frame_size;
+    }
+
+    return r;
+}
+
+static void uninit(struct af_instance *af)
+{
+    talloc_free(af->setup);
+}
+
+static int af_open(struct af_instance *af)
+{
+    af->control = control;
+    af->uninit = uninit;
+    af->play = play;
+    af->mul = 1;
+    struct priv *priv = talloc_zero(NULL, struct priv);
+    af->setup = priv;
+    af->data = &priv->data;
+    return AF_OK;
+}
+
+struct af_info af_info_lavfi = {
+    "libavfilter bridge",
+    "lavfi",
+    "",
+    "",
+    0,
+    af_open
+};

configure

@@ -329,6 +329,7 @@ Optional features:
   --disable-libavdevice  enable libavdevice demuxers [autodetect]
   --disable-libavfilter  enable libavfilter [autodetect]
   --disable-vf-lavfi     enable vf_lavfi libavfilter bridge [audodetect]
+  --disable-af-lavfi     enable af_lavfi libavfilter bridge [audodetect]
 
 Codecs:
   --enable-mng              enable MNG input support [autodetect]
@@ -487,6 +488,7 @@ _rpath=no
 libpostproc=auto
 libavfilter=auto
 vf_lavfi=auto
+af_lavfi=auto
 libavdevice=auto
 _stream_cache=yes
 _priority=no
@@ -703,6 +705,8 @@ for ac_option do
   --disable-libavfilter) libavfilter=no ;;
   --enable-vf-lavfi)    vf_lavfi=auto ;;
   --disable-vf-lavfi)   vf_lavfi=no ;;
+  --enable-af-lavfi)    af_lavfi=auto ;;
+  --disable-af-lavfi)   af_lavfi=no ;;
 
   --enable-enca)        _enca=yes       ;;
   --disable-enca)       _enca=no        ;;
@@ -2750,6 +2754,31 @@ fi
 echores "$vf_lavfi"
 
 
+echocheck "libavutil av_opt_set_int_list() API"
+_avutil_has_opt_set_int_list=no
+statement_check libavutil/opt.h 'av_opt_set_int_list(0,0,(int*)0,0,0)' && _avutil_has_opt_set_int_list=yes
+echores "$_avutil_has_opt_set_int_list"
+
+
+echocheck "using libavfilter through af_lavfi"
+if test "$af_lavfi" = auto ; then
+    af_lavfi=no
+    if test "$libavfilter" = yes ; then
+        if test "$_avutil_has_opt_set_int_list" = no ; then
+            res_comment="libavutil too old"
+        else
+            af_lavfi=yes
+        fi
+    fi
+fi
+if test "$af_lavfi" = yes ; then
+    def_af_lavfi='#define CONFIG_AF_LAVFI 1'
+else
+    def_af_lavfi='#undef CONFIG_AF_LAVFI'
+fi
+echores "$af_lavfi"
+
+
 echocheck "libavdevice >= 54.0.0"
 if test "$libavdevice" = auto ; then
     libavdevice=no
@@ -3087,6 +3116,7 @@ LIBPOSTPROC = $libpostproc
 LIBAVDEVICE = $libavdevice
 LIBAVFILTER = $libavfilter
 VF_LAVFI = $vf_lavfi
+AF_LAVFI = $af_lavfi
 LIBSMBCLIENT = $_smb
 LIBQUVI = $_libquvi
 LIBTHEORA = $_theora
@@ -3242,6 +3272,7 @@ $def_libpostproc
 $def_libavdevice
 $def_libavfilter
 $def_vf_lavfi
+$def_af_lavfi
 
 
 /* Audio output drivers */