[FFmpeg-devel] [PATCH 2/2] lavfi: add audio silencedetect filter.

Stefano Sabatini stefasab at gmail.com
Sat Jan 7 21:37:09 CET 2012


On date Saturday 2012-01-07 15:41:05 +0100, Clément Bœsch encoded:
> On Thu, Jan 05, 2012 at 08:29:35PM +0100, Nicolas George wrote:
[...]
> From 2e7c6e75d225818b0eacf29f5599dfd308804406 Mon Sep 17 00:00:00 2001
> From: =?UTF-8?q?Cl=C3=A9ment=20B=C5=93sch?= <ubitux at gmail.com>
> Date: Tue, 3 Jan 2012 23:47:09 +0100
> Subject: [PATCH] lavfi: add audio silencedetect filter.
> 
> ---
>  Changelog                      |    1 +
>  doc/filters.texi               |   24 ++++++
>  libavfilter/Makefile           |    1 +
>  libavfilter/af_silencedetect.c |  171 ++++++++++++++++++++++++++++++++++++++++
>  libavfilter/allfilters.c       |    1 +
>  libavfilter/avfilter.h         |    4 +-
>  6 files changed, 200 insertions(+), 2 deletions(-)
>  create mode 100644 libavfilter/af_silencedetect.c
> 
> diff --git a/Changelog b/Changelog
> index db4c7b3..d4ec698 100644
> --- a/Changelog
> +++ b/Changelog
> @@ -19,6 +19,7 @@ version next:
>  - Avid 1:1 10-bit RGB Packer decoder
>  - v308 Quicktime Uncompressed 4:4:4 encoder and decoder
>  - yuv4 libquicktime packed 4:2:0 encoder and decoder
> +- silencedetect audio filter
>  
>  
>  version 0.9:
> diff --git a/doc/filters.texi b/doc/filters.texi
> index de73e3f..3bc117c 100644
> --- a/doc/filters.texi
> +++ b/doc/filters.texi
> @@ -358,6 +358,30 @@ Note that @command{ffmpeg} integrates a default down-mix (and up-mix) system
>  that should be preferred (see "-ac" option) unless you have very specific
>  needs.
>  
> + at section silencedetect
> +
> +Print a notification line when silence is detected, or when sound is back in
> +the given audio stream.

This needs more explanation. For example:

This filter logs a message when detect that the input audio volume is
less or equal to the noise tolerance value set with @option{noise} for
a duration greater or equal to the silence duration value set with
@option{duration}.

> +
> + at table @option
> + at item d, duration
> +Set silence duration until notification (default is 2 seconds).
> +
> + at item noise, n
> +Set noise tolerance. Can be specified in dB or amplitude ratio. Default is

in db (in case "dB" is appended to the specified value).

> +-60dB, or 0.001.
> + at end table
> +
> +Detect 5 seconds of silence with -50dB noise tolerance:
> + at example
> +silencedetect=n=-50dB:d=5
> + at end example
> +
> +Complete example with ffmpeg to detect silence with 0.0001 noise tolerance:
> + at example
> +ffmpeg -f lavfi -i amovie=silence.mp3,silencedetect=noise=0.0001 -f null -
> + at end example
> +
>  @section volume
>  
>  Adjust the input audio volume.
> diff --git a/libavfilter/Makefile b/libavfilter/Makefile
> index 0d8f120..bb5748b 100644
> --- a/libavfilter/Makefile
> +++ b/libavfilter/Makefile
> @@ -35,6 +35,7 @@ OBJS-$(CONFIG_ASTREAMSYNC_FILTER)            += af_astreamsync.o
>  OBJS-$(CONFIG_EARWAX_FILTER)                 += af_earwax.o
>  OBJS-$(CONFIG_PAN_FILTER)                    += af_pan.o
>  OBJS-$(CONFIG_VOLUME_FILTER)                 += af_volume.o
> +OBJS-$(CONFIG_SILENCEDETECT_FILTER)          += af_silencedetect.o
>  
>  OBJS-$(CONFIG_ABUFFER_FILTER)                += asrc_abuffer.o
>  OBJS-$(CONFIG_AEVALSRC_FILTER)               += asrc_aevalsrc.o
> diff --git a/libavfilter/af_silencedetect.c b/libavfilter/af_silencedetect.c
> new file mode 100644
> index 0000000..fe798dc
> --- /dev/null
> +++ b/libavfilter/af_silencedetect.c
> @@ -0,0 +1,171 @@
> +/*
> + * This file is part of FFmpeg.
> + *
> + * Copyright (c) 2011 Clément Bœsch <ubitux at gmail.com>
> + *
> + * 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
> + * Audio silence detector
> + */
> +
> +#include "libavutil/opt.h"
> +#include "avfilter.h"
> +
> +typedef struct {
> +    const AVClass *class;
> +    char *noise_str;            ///< noise option string
> +    double noise;               ///< noise amplitude ratio
> +    int duration;               ///< minimum duration to monitor in seconds
> +    int64_t nb_null_samples;    ///< current number of continuous zero samples
> +    double start;               ///< if silence is detected, this value contains the time of the first zero sample
> +    int last_sample_rate;       ///< last sample rate to check for sample rate changes
> +} SilenceDetectContext;
> +
> +#define OFFSET(x) offsetof(SilenceDetectContext, x)
> +static const AVOption silencedetect_options[] = {
> +    { "n",         "set noise tolerance",              OFFSET(noise_str), AV_OPT_TYPE_STRING, {.str="-60dB"}, CHAR_MIN, CHAR_MAX },
> +    { "noise",     "set noise tolerance",              OFFSET(noise_str), AV_OPT_TYPE_STRING, {.str="-60dB"}, CHAR_MIN, CHAR_MAX },
> +    { "d",         "set minimum duration in seconds",  OFFSET(duration),  AV_OPT_TYPE_INT,    {.dbl=2},    0, INT_MAX},
> +    { "duration",  "set minimum duration in seconds",  OFFSET(duration),  AV_OPT_TYPE_INT,    {.dbl=2},    0, INT_MAX},
> +    { NULL },
> +};
> +
> +static const char *silencedetect_get_name(void *ctx)
> +{
> +    return "silencedetect";
> +}
> +
> +static const AVClass silencedetect_class = {
> +    .class_name = "SilenceDetectContext",
> +    .item_name  = silencedetect_get_name,
> +    .option     = silencedetect_options,
> +};
> +
> +static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
> +{
> +    int ret;
> +    char *tail;
> +    SilenceDetectContext *silence = ctx->priv;
> +
> +    silence->class = &silencedetect_class;
> +    av_opt_set_defaults(silence);
> +
> +    if ((ret = av_set_options_string(silence, args, "=", ":")) < 0) {
> +        av_log(ctx, AV_LOG_ERROR, "Error parsing options string: '%s'\n", args);
> +        return ret;
> +    }
> +

> +    silence->noise = strtod(silence->noise_str, &tail);
> +    if (!strcmp(tail, "dB"))
> +        silence->noise = pow(10, silence->noise/20);

Alternatively you may want to create an internal function, to share
with af_volume(). Also this is missing a check, in case noise_str
contains a foobar value.

> +    return 0;
> +}
> +
> +static void filter_samples(AVFilterLink *inlink, AVFilterBufferRef *insamples)
> +{
> +    int i;
> +    SilenceDetectContext *silence = inlink->dst->priv;
> +    const int     nb_channels       = av_get_channel_layout_nb_channels(inlink->channel_layout);
> +    const int     nb_samples        = insamples->audio->nb_samples            * nb_channels;

> +    const int64_t nb_samples_notify = inlink->sample_rate * silence->duration * nb_channels;

alternatively you can cache nb_samples_notify, and update it when
sample_rate changes.

> +
> +    if (silence->last_sample_rate &&
> +        silence->last_sample_rate != inlink->sample_rate) {
> +        av_log(silence, AV_LOG_WARNING,
> +               "Sample rate changed, detection might not be accurate\n");
> +        silence->start = silence->nb_null_samples = 0;
> +    }
> +    silence->last_sample_rate = inlink->sample_rate;
> +
> +    // TODO: support more sample formats
> +    if (insamples->format == AV_SAMPLE_FMT_DBL) {
> +        double *p = (double *)insamples->data[0];
> +
> +        for (i = 0; i < nb_samples; i++, p++) {
> +            if (*p < silence->noise && *p > -silence->noise) {
> +                if (!silence->start) {
> +                    silence->nb_null_samples++;
> +                    if (silence->nb_null_samples == nb_samples_notify) {
> +                        silence->start = insamples->pts * av_q2d(inlink->time_base) - silence->duration;

> +                        av_log(silence, AV_LOG_INFO,
> +                               "Silence detected at %f sec\n", silence->start);

what about "silence_start:%f"
=> easier to grep

> +                    }
> +                }
> +            } else {
> +                if (silence->start) {
> +                    double end = insamples->pts * av_q2d(inlink->time_base);
> +                    av_log(silence, AV_LOG_INFO,
> +                           "Silence ended at %f sec (duration: %f sec)\n",

same here:
"silence_end:%f silence_duration:%s"

[...]
-- 
FFmpeg = Fast and Frightening Multipurpose Pontificating Everlasting God


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