[FFmpeg-devel] [PATCH] lavfi: add audio eval signal source

Stefano Sabatini stefasab at gmail.com
Thu Oct 13 02:08:57 CEST 2011


From: Stefano Sabatini <stefano.sabatini-lala at poste.it>

---
 doc/filters.texi            |   70 +++++++++++++++
 libavfilter/Makefile        |    1 +
 libavfilter/allfilters.c    |    1 +
 libavfilter/asrc_aevalsrc.c |  197 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 269 insertions(+), 0 deletions(-)
 create mode 100644 libavfilter/asrc_aevalsrc.c

diff --git a/doc/filters.texi b/doc/filters.texi
index 54c1417..339489f 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -275,6 +275,76 @@ equivalent to:
 abuffer=44100:1:3:1
 @end example
 
+ at section aevalsrc
+
+Generate an audio signal generated by an expression.
+
+This source accepts in input an expression, which is evaluated and
+used for generating a mono audio signal.
+
+It accepts the syntax: @var{expr}[:@var{options}] where @var{expr} is
+the expression to evaluate, and @var{options} is an optional sequence
+of @var{key}=@var{value} pairs, separated by ":".
+
+The description of the accepted options follows.
+
+ at table @option
+
+ at item nb_samples, n
+Set the number of samples per requested frames.
+
+ at item sample_rate, s
+Specify the sample rate, and defaults to 44100.
+ at end table
+
+The expression in @var{expr} can contain the following constants:
+
+ at table @option
+ at item E, PI, PHI
+the corresponding mathematical approximated values for e
+(euler number), pi (greek PI), PHI (golden ratio)
+
+ at item n
+the number of sample, starting from 0
+
+ at item t
+time of the sample expressed in second, starting from 0
+
+ at item s
+sample rate
+
+ at end table
+
+ at subsection Examples
+
+ at itemize
+
+ at item
+Generate silence:
+ at example
+aevalsrc=0
+ at end example
+
+ at item
+Generate a sin signal with frequence 4400 Hz:
+ at example
+aevalsrc="sin(4400*t)"
+ at end example
+
+ at item
+Generate white noise:
+ at example
+aevalsrc="-2+random(0)"
+ at end example
+
+ at item
+Generate amplitude modulated signal:
+ at example
+aevalsrc="sin(10*t)*sin(8800*t)"
+ at end example
+
+ at end itemize
+
 @section amovie
 
 Read an audio stream from a movie container.
diff --git a/libavfilter/Makefile b/libavfilter/Makefile
index 7086753..08a69e4 100644
--- a/libavfilter/Makefile
+++ b/libavfilter/Makefile
@@ -30,6 +30,7 @@ OBJS-$(CONFIG_ARESAMPLE_FILTER)              += af_aresample.o
 OBJS-$(CONFIG_ASHOWINFO_FILTER)              += af_ashowinfo.o
 
 OBJS-$(CONFIG_ABUFFER_FILTER)                += asrc_abuffer.o
+OBJS-$(CONFIG_AEVALSRC_FILTER)               += asrc_aevalsrc.o
 OBJS-$(CONFIG_AMOVIE_FILTER)                 += src_movie.o
 OBJS-$(CONFIG_ANULLSRC_FILTER)               += asrc_anullsrc.o
 
diff --git a/libavfilter/allfilters.c b/libavfilter/allfilters.c
index 2bb42a1..3c77adb 100644
--- a/libavfilter/allfilters.c
+++ b/libavfilter/allfilters.c
@@ -41,6 +41,7 @@ void avfilter_register_all(void)
     REGISTER_FILTER (ASHOWINFO,   ashowinfo,   af);
 
     REGISTER_FILTER (ABUFFER,     abuffer,     asrc);
+    REGISTER_FILTER (AEVALSRC,    aevalsrc,    asrc);
     REGISTER_FILTER (AMOVIE,      amovie,      asrc);
     REGISTER_FILTER (ANULLSRC,    anullsrc,    asrc);
 
diff --git a/libavfilter/asrc_aevalsrc.c b/libavfilter/asrc_aevalsrc.c
new file mode 100644
index 0000000..189d60d
--- /dev/null
+++ b/libavfilter/asrc_aevalsrc.c
@@ -0,0 +1,197 @@
+/*
+ * Copyright (c) 2011 Stefano Sabatini
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * eval audio source
+ */
+
+#include "libavutil/audioconvert.h"
+#include "libavutil/avstring.h"
+#include "libavutil/eval.h"
+#include "libavutil/opt.h"
+#include "avfilter.h"
+#include "internal.h"
+
+static const char *var_names[] = {
+    "E",
+    "PHI",
+    "PI",
+    "n",            ///< number of frame
+    "t",            ///< timestamp expressed in seconds
+    "s",            ///< sample rate, same as 1/tb
+    NULL
+};
+
+enum var_name {
+    VAR_E,
+    VAR_PHI,
+    VAR_PI,
+    VAR_N,
+    VAR_T,
+    VAR_S,
+    VAR_VARS_NB
+};
+
+typedef struct {
+    const AVClass *class;
+    char *sample_rate_str;
+    int sample_rate;
+    int64_t pts;
+    AVExpr *expr;
+    char *expr_str;
+    int nb_samples;             ///< number of samples per requested frame
+    uint64_t n;
+    double var_values[VAR_VARS_NB];
+} EvalContext;
+
+#define OFFSET(x) offsetof(EvalContext, x)
+
+static const AVOption eval_options[]= {
+    { "nb_samples",     "set the number of samples per requested frame", OFFSET(nb_samples), FF_OPT_TYPE_INT, {.dbl = 1024}, 0, INT_MAX },
+    { "n",              "set the number of samples per requested frame", OFFSET(nb_samples), FF_OPT_TYPE_INT, {.dbl = 1024}, 0, INT_MAX },
+    { "sample_rate", "set the sample rate", OFFSET(sample_rate_str), FF_OPT_TYPE_STRING, {.str = "44100"}, 0, INT_MAX },
+    { "s", "set the sample rate", OFFSET(sample_rate_str), FF_OPT_TYPE_STRING, {.str = "44100"}, 0, INT_MAX },
+{NULL},
+};
+
+static const char *eval_get_name(void *ctx)
+{
+    return "aevalsrc";
+}
+
+static const AVClass eval_class = {
+    "AEvalSrcContext",
+    eval_get_name,
+    eval_options
+};
+
+static int init(AVFilterContext *ctx, const char *args, void *opaque)
+{
+    EvalContext *eval = ctx->priv;
+    int ret;
+
+    eval->class = &eval_class;
+    av_opt_set_defaults(eval);
+
+    if (args)
+        eval->expr_str = av_get_token(&args, ":");
+    if (!eval->expr_str || !*eval->expr_str) {
+        av_log(ctx, AV_LOG_ERROR, "No expression provided!\n");
+        return AVERROR(EINVAL);
+    }
+
+    if ((ret = av_expr_parse(&eval->expr, eval->expr_str, var_names,
+                             NULL, NULL, NULL, NULL, 0, ctx)) < 0)
+        return ret;
+
+    if (*args++ == ':' && (ret = av_set_options_string(eval, args, "=", ":")) < 0) {
+        av_log(ctx, AV_LOG_ERROR, "Error parsing options string: '%s'\n", args);
+        return ret;
+    }
+
+    if ((ret = ff_parse_sample_rate(&eval->sample_rate, eval->sample_rate_str, ctx)))
+        return ret;
+    eval->n = 0;
+
+    return 0;
+}
+
+static void uninit(AVFilterContext *ctx)
+{
+    EvalContext *eval = ctx->priv;
+
+    av_expr_free(eval->expr); eval->expr = NULL;
+    av_freep(&eval->expr_str);
+    av_freep(&eval->sample_rate_str);
+}
+
+static int config_props(AVFilterLink *outlink)
+{
+    EvalContext *eval = outlink->src->priv;
+
+    outlink->time_base = (AVRational){1, eval->sample_rate};
+    outlink->sample_rate = eval->sample_rate;
+
+    eval->var_values[VAR_S]  = eval->sample_rate;
+
+    av_log(outlink->src, AV_LOG_INFO,
+           "sample_rate:%d expr:'%s'\n", eval->sample_rate, eval->expr_str);
+
+    return 0;
+}
+
+static int query_formats(AVFilterContext *ctx)
+{
+    enum AVSampleFormat sample_fmts[] = { AV_SAMPLE_FMT_DBL, AV_SAMPLE_FMT_NONE };
+    int64_t chlayouts[] = { AV_CH_LAYOUT_MONO, -1 };
+    int packing_fmts[] = { AVFILTER_PACKED, -1 };
+
+    avfilter_set_common_sample_formats (ctx, avfilter_make_format_list(sample_fmts));
+    avfilter_set_common_channel_layouts(ctx, avfilter_make_format64_list(chlayouts));
+    avfilter_set_common_packing_formats(ctx, avfilter_make_format_list(packing_fmts));
+
+    return 0;
+}
+
+static int request_frame(AVFilterLink *outlink)
+{
+    EvalContext *eval = outlink->src->priv;
+    AVFilterBufferRef *samplesref;
+    int i;
+
+    samplesref = avfilter_get_audio_buffer(outlink, AV_PERM_WRITE, eval->nb_samples);
+    eval->var_values[VAR_N] = eval->n;
+
+    /* evaluate expression for each single sample */
+    for (i = 0; i < eval->nb_samples; i++) {
+        eval->var_values[VAR_T] = eval->var_values[VAR_N] * (double)1/eval->sample_rate;
+        *((double *) samplesref->data[0] + i) =
+            av_expr_eval(eval->expr, eval->var_values, NULL);
+        eval->var_values[VAR_N] = eval->n++;
+    }
+
+    samplesref->pts = eval->pts;
+    samplesref->pos = -1;
+    samplesref->audio->sample_rate = eval->sample_rate;
+    eval->pts += eval->nb_samples;
+
+    avfilter_filter_samples(outlink, samplesref);
+
+    return 0;
+}
+
+AVFilter avfilter_asrc_aevalsrc = {
+    .name        = "aevalsrc",
+    .description = NULL_IF_CONFIG_SMALL("Generate an audio signal generated by an expression."),
+
+    .query_formats = query_formats,
+    .init        = init,
+    .uninit      = uninit,
+    .priv_size   = sizeof(EvalContext),
+
+    .inputs      = (AVFilterPad[]) {{ .name = NULL}},
+
+    .outputs     = (AVFilterPad[]) {{ .name = "default",
+                                      .type = AVMEDIA_TYPE_AUDIO,
+                                      .config_props = config_props,
+                                      .request_frame = request_frame, },
+                                    { .name = NULL}},
+};
-- 
1.7.4.1



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