Fang Yibo:
> Re: [FFmpeg-devel,v2,0/2] avfilter: add PCM dumping between filters for audio
> debugging
>
> From: Yibo Fang <blueybf...@outlook.com>
> Subject: [FFmpeg-devel,v2,0/2] avfilter: add PCM dumping between filters for
> audio debugging
> Date: Wed, 23 Apr 2025 10:57:00 +0800
> Message-Id: <cover.0.2@ffmpeg>
>
> This series adds a debugging feature that lets developers dump raw
> PCM audio between filters. The data are written to files in a user-
> selected directory via two new commands:
>
> dump_raw_start file=/path/to/dir/
> dump_raw_stop
>
> Planar audio is automatically interleaved; only audio links are
> affected. Patch 1/2 implements the feature, patch 2/2 documents it.
>
> Regards,
> Yibo Fang
>
> ---
>
> From 2df56e74273d477ae27003e0981220749a6b58cf Mon Sep 17 00:00:00 2001
> From: Yibo Fang <blueybf...@outlook.com>
> Date: Wed, 23 Apr 2025 10:58:55 +0800
> Subject: [PATCH 1/2] avfilter: add PCM dumping between filters for audio
> debugging
>
> This patch introduces PCM dumping support between AVFilter links,
> intended for audio debugging and filter-graph inspection.
>
> Two filter commands are added:
>
> dump_raw_start file=/path/to/output/dir/
> dump_raw_stop
>
> When dumping is enabled, audio leaving the selected filter output is
> written to an automatically named file:
>
> <src_filter>-<dst_filter>.pcm
>
> Planar formats are converted to packed. File descriptors are opened
> on demand and closed automatically. Works only on audio links.
>
> Example (C API):
> avfilter_process_command(filter, "dump_raw_start",
> "file=/tmp/", NULL, 0, 0);
>
> Signed-off-by: Yibo Fang <blueybf...@outlook.com>
> ---
> libavfilter/avfilter.c | 144 +++++++++++++++++++++++++++++++++++++++++
> libavfilter/avfilter.h | 5 ++
> 2 files changed, 149 insertions(+)
>
> diff --git a/libavfilter/avfilter.c b/libavfilter/avfilter.c
> index 64c1075c40..b7034569db 100644
> --- a/libavfilter/avfilter.c
> +++ b/libavfilter/avfilter.c
> @@ -19,6 +19,9 @@
> * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
> USA
> */
>
> +#include <fcntl.h>
> +#include <unistd.h>
> +
> #include "libavutil/avassert.h"
> #include "libavutil/avstring.h"
> #include "libavutil/bprint.h"
> @@
> return 0;
> }
>
> +/* ---------- PCM dump helpers ---------- */
> +
> +static av_cold void link_uninit_dump_pcm(AVFilterLink *link)
> +{
> + if (link->dump_pcm_fds) {
> + for (unsigned i = 0; i < link->nb_dump_pcm_fds; i++)
> + if (link->dump_pcm_fds[i] >= 0)
> + close(link->dump_pcm_fds[i]);
> + av_freep(&link->dump_pcm_fds);
> + link->nb_dump_pcm_fds = 0;
> + }
> + av_freep(&link->dump_pcm_path);
> + link->dump_pcm = 0;
> +}
> +
> +static av_cold int link_init_dump_pcm(AVFilterLink *link)
> +{
> + /* build full path "<dir>/<src>-<dst>.pcm" */
> + const char *dir = link->dump_pcm_path;
> + const char *sep = dir[strlen(dir) - 1] == '/' ? "" : "/";
> + char path[4096];
> + snprintf(path, sizeof(path), "%s%s%.16s-%.8s.pcm",
> + dir, sep, link->src->name, link->dst->name);
> +
> + link->nb_dump_pcm_fds = 1;
> + link->dump_pcm_fds = av_malloc(sizeof(int));
> + if (!link->dump_pcm_fds)
> + return AVERROR(ENOMEM);
> +
> + int fd = open(path, O_WRONLY | O_CREAT | O_TRUNC | O_EXCL, 0644);
> + if (fd < 0) {
> + link_uninit_dump_pcm(link);
> + return AVERROR(errno);
> + }
> + link->dump_pcm_fds[0] = fd;
> + av_log(link->dst, AV_LOG_INFO, "PCM dump file: %s\n", path);
> + return 0;
> +}
> +
> +static int filter_set_dump_pcm(AVFilterContext *f, const char *arg, int set)
> +{
> + const char *prefix = "file=";
> + if (!arg || av_strncasecmp(arg, prefix, strlen(prefix))) {
> + av_log(f, AV_LOG_ERROR,
> + "dump_raw_* expects argument file=/dir/\n");
> + return AVERROR(EINVAL);
> + }
> + const char *dir = arg + strlen(prefix);
> +
> + for (int i = 0; i < f->nb_outputs; i++) {
> + AVFilterLink *l = f->outputs[i];
> + if (l->type != AVMEDIA_TYPE_AUDIO)
> + continue;
> + if (set) {
> + av_freep(&l->dump_pcm_path);
> + l->dump_pcm_path = av_strdup(dir);
> + if (!l->dump_pcm_path)
> + return AVERROR(ENOMEM);
> + l->dump_pcm = 1;
> + } else
> + link_uninit_dump_pcm(l);
> + }
> + return 0;
> +}
> +
> +/* write one frame */
> +static int link_dump_frame(AVFilterLink *link, AVFrame *frame)
> +{
> + int ret;
> + if (!link->dump_pcm_fds &&
> + (ret = link_init_dump_pcm(link)) < 0)
> + return ret;
> +
> + const int ch = frame->ch_layout.nb_channels;
> + const int bps = av_get_bytes_per_sample(frame->format);
> + const int ns = frame->nb_samples;
> + const int totlen = ch * ns * bps;
> +
> + /* interleave planar to packed if necessary */
> + if (av_sample_fmt_is_planar(frame->format)) {
> + uint8_t *buf = av_malloc(totlen);
> + if (!buf)
> + return AVERROR(ENOMEM);
> + for (int s = 0; s < ns; s++)
> + for (int c = 0; c < ch; c++)
> + memcpy(buf + (s*ch + c)*bps,
> + (uint8_t*)frame->extended_data[c] + s*bps,
> + bps);
> + ret = write(link->dump_pcm_fds[0], buf, totlen);
> + av_free(buf);
> + } else
> + ret = write(link->dump_pcm_fds[0], frame->data[0], totlen);
> +
> + if (ret < 0) {
> + av_log(link->dst, AV_LOG_ERROR, "PCM dump write failed: %s\n",
> + av_err2str(ret));
> + link_uninit_dump_pcm(link);
> + return ret;
> + }
> + return 0;
> +}
> +
> static void link_free(AVFilterLink **link)
> {
> @@
>
> int avfilter_process_command(AVFilterContext *filter, const char *cmd,
> const char *arg, char *res, int res_len, int
> flags)
> {
> @@
> - if (res == local_res)
> - av_log(filter, AV_LOG_INFO, "%s", res);
> - return 0;
> + if (res == local_res)
> + av_log(filter, AV_LOG_INFO, "%s", res);
> + return 0;
> + } else if (!strcmp(cmd, "dump_raw_start")) {
> + return filter_set_dump_pcm(filter, arg, 1);
> + } else if (!strcmp(cmd, "dump_raw_stop")) {
> + return filter_set_dump_pcm(filter, arg, 0);
> } else if(!strcmp(cmd, "enable")) {
> return set_enable_expr(fffilterctx(filter), arg);
> @@
> /* ... existing code ... */
>
> + if (link->dump_pcm && link->type == AVMEDIA_TYPE_AUDIO) {
> + ret = link_dump_frame(link, frame);
> + if (ret < 0)
> + av_log(link->dst, AV_LOG_ERROR,
> + "PCM dump failed with %s\n", av_err2str(ret));
> + }
> +
> li->frame_blocked_in = li->frame_wanted_out = 0;
> @@
> diff --git a/libavfilter/avfilter.h b/libavfilter/avfilter.h
> index a89d3cf658..0d4c91bb6b 100644
> --- a/libavfilter/avfilter.h
> +++ b/libavfilter/avfilter.h
> @@
> AVChannelLayout ch_layout; ///< channel layout of current buffer
>
> + int dump_pcm; ///< enable dumping on this link
> + int *dump_pcm_fds; ///< one FD per link (currently 1)
> + unsigned nb_dump_pcm_fds; ///< number of FDs
> + char *dump_pcm_path; ///< user-supplied directory
> +
> /**
> * Define the time base used by the PTS of the frames/samples
> * which will pass through this link.
> --
> 2.34.1
>
> ---
>
> From 8cf7bfa52a10be87e0f17b9783159b0e83f960f7 Mon Sep 17 00:00:00 2001
> From: Yibo Fang <blueybf...@outlook.com>
> Date: Wed, 23 Apr 2025 12:38:00 +0800
> Subject: [PATCH 2/2] doc/filters: document dump_raw_start and dump_raw_stop
> commands
>
> Signed-off-by: Yibo Fang <blueybf...@outlook.com>
> ---
> doc/filters.texi | 45 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 45 insertions(+)
>
> diff --git a/doc/filters.texi b/doc/filters.texi
> index 45b3e03e5e..6a2d23df3f 100644
> --- a/doc/filters.texi
> +++ b/doc/filters.texi
> @@
> @section adumppcm
>
> Dump raw PCM audio data for debugging between filters.
>
> This filter allows writing raw audio data to disk from any audio link
> in the filtergraph for inspection. It supports planar and packed formats,
> automatically interleaving planar data for writing.
>
> @subsection Syntax
>
> @example
> dump_raw_start=file=/your/dump/directory/
> @end example
>
> @subsection Usage
>
> To enable dumping, use the @code{dump_raw_start} command:
>
> @example
> ffmpeg -i input.wav -af "volume,asendcmd='0.0 dump_raw_start
> file=/tmp/pcm/'" -f null -
> @end example
>
> To stop dumping:
>
> @example
> asendcmd='5.0 dump_raw_stop'
> @end example
>
> @subsection Options
>
> @table @option
> @item file
> Specify a directory path (not a filename) where PCM data will be dumped.
> The dumped file is named @code{<src>-<dst>.pcm} and will be overwritten if
> it already exists.
> @end table
> --
> 2.34.1
>
>
>
> ________________________________
> From: ffmpeg-devel <ffmpeg-devel-boun...@ffmpeg.org> on behalf of Andreas
> Rheinhardt <andreas.rheinha...@outlook.com>
> Sent: 26 April 2025 3:00
> To: ffmpeg-devel@ffmpeg.org <ffmpeg-devel@ffmpeg.org>
> Subject: Re: [FFmpeg-devel] [PATCH] avfilter: add PCM dumping between filters
> for audio debugging
>
> 一只大 肥猫:
>> This patch introduces PCM dumping support between AVFilter links, intended
>> for audio debugging.
>>
>> It adds a configure-time option `--dumpdir=PATH` to specify the output
>> directory for raw PCM data (default: /tmp/).
>>
>> Two commands are exposed to control dumping:
>> - dump_raw_start <dst_filter_name>
>> - dump_raw_stop <dst_filter_name>
>>
>> Dump files are written as: srcname-dstname-channel.pcm
>>
>> Supports packed and planar formats. File descriptors are managed
>> automatically and work only on audio links.
>>
>> Example usage:
>> avfilter_process_command(filter, "dump_raw_start", "volume", NULL, 0, 0);
>>
>> This feature helps developers debug filter behavior by inspecting
>> intermediate audio data.
>> ---
>> From 6a31c85afd2800c09076c1e2b7c734c7b719f73d Mon Sep 17 00:00:00 2001
>> From: Yibo Fang <blueybf...@outlook.com>
>> Date: Wed, 23 Apr 2025 09:17:51 +0800
>> Subject: [PATCH 1/1] avfilter: add PCM dumping between filters for audio
>> debugging
>>
>> This patch adds the ability to dump raw PCM audio data between AVFilter
>> links.
>> It introduces a configure-time option `--dumpdir=PATH` to control the output
>> directory of dump files (default: /tmp/). This feature is helpful for
>> debugging
>> filter behavior and verifying audio processing.
>>
>> Two filter commands are added:
>> - dump_raw_start <dst_filter_name>
>> - dump_raw_stop <dst_filter_name>
>>
>> The PCM files are written in the format: srcname-dstname-<channel>.pcm.
>>
>> Supports both packed and planar formats. File descriptors are automatically
>> managed. Works only on audio links.
>>
>> Example usage:
>> avfilter_process_command(filter, "dump_raw_start", "volume", NULL, 0, 0);
>>
>> Signed-off-by: Yibo Fang <blueybf...@outlook.com>
>> ---
>> configure | 7 +++
>> libavfilter/avfilter.c | 110 +++++++++++++++++++++++++++++++++++++++++
>> libavfilter/avfilter.h | 4 ++
>> 3 files changed, 121 insertions(+)
>>
>> diff --git a/configure b/configure
>> index c94b8eac43..381633749d 100755
>> --- a/configure
>> +++ b/configure
>> @@ -524,6 +524,7 @@ Developer options (useful when working on FFmpeg itself):
>> --disable-large-tests disable tests that use a large amount of memory
>> --disable-ptx-compression don't compress CUDA PTX code even when possible
>> --disable-version-tracking don't include the git/release version in the
>> build
>> + --dumpdir=PATH location of pcm dump files to save.
>>
>> NOTE: Object files are built at the place where configure is launched.
>> EOF
>> @@ -2690,6 +2691,7 @@ PATHS_LIST="
>> prefix
>> shlibdir
>> install_name_dir
>> + dumpdir
>> "
>>
>> CMDLINE_SET="
>> @@ -4123,6 +4125,9 @@ incdir_default='${prefix}/include'
>> libdir_default='${prefix}/lib'
>> mandir_default='${prefix}/share/man'
>>
>> +# runtime path
>> +dumpdir_default='/tmp/'
>> +
>> # toolchain
>> ar_default="ar"
>> cc_default="gcc"
>> @@ -8118,6 +8123,7 @@ DOCDIR=\$(DESTDIR)$docdir
>> MANDIR=\$(DESTDIR)$mandir
>> PKGCONFIGDIR=\$(DESTDIR)$pkgconfigdir
>> INSTALL_NAME_DIR=$install_name_dir
>> +DUMPDIR=$dumpdir
>> SRC_PATH=$source_path
>> SRC_LINK=$source_link
>> ifndef MAIN_MAKEFILE
>> @@ -8267,6 +8273,7 @@ cat > $TMPH <<EOF
>> #define CONFIG_THIS_YEAR 2025
>> #define FFMPEG_DATADIR "$(eval c_escape $datadir)"
>> #define AVCONV_DATADIR "$(eval c_escape $datadir)"
>> +#define FFMPEG_DUMPDIR "$(eval c_escape $dumpdir)"
>> #define CC_IDENT "$(c_escape ${cc_ident:-Unknown compiler})"
>> #define OS_NAME $target_os
>> #define EXTERN_PREFIX "${extern_prefix}"
>> diff --git a/libavfilter/avfilter.c b/libavfilter/avfilter.c
>> index 64c1075c40..9fc6308544 100644
>> --- a/libavfilter/avfilter.c
>> +++ b/libavfilter/avfilter.c
>> @@ -19,6 +19,9 @@
>> * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301
>> USA
>> */
>>
>> +#include <fcntl.h>
>> +#include <unistd.h>
>> +
>> #include "libavutil/avassert.h"
>> #include "libavutil/avstring.h"
>> #include "libavutil/bprint.h"
>> @@ -195,6 +198,66 @@ int avfilter_link(AVFilterContext *src, unsigned srcpad,
>> return 0;
>> }
>>
>> +static av_cold void link_uninit_dump_pcm(AVFilterLink *link, int stop)
>> +{
>> + if (link->dump_pcm_fds) {
>> + int i;
>> + for (i = 0; i < link->nb_dump_pcm_fds; i++) {
>> + if (link->dump_pcm_fds[i])
>> + close(link->dump_pcm_fds[i]);
>> + }
>> + av_free(link->dump_pcm_fds);
>> + link->dump_pcm_fds = NULL;
>> + link->nb_dump_pcm_fds = 0;
>> + }
>> +
>> + if (stop)
>> + link->dump_pcm = 0;
>> +}
>> +
>> +static av_cold int link_init_dump_pcm(AVFilterLink *link)
>> +{
>> + char path[4096];
>> + int fd, i;
>> +
>> + link->nb_dump_pcm_fds = av_sample_fmt_is_planar(link->format)?
>> link->ch_layout.nb_channels : 1;
>> + link->dump_pcm_fds = av_malloc_array(link->nb_dump_pcm_fds,
>> sizeof(int));
>> + if (!link->dump_pcm_fds)
>> + return AVERROR(ENOMEM);
>> +
>> + for (i = 0; i < link->nb_dump_pcm_fds; i++) {
>> + snprintf(path, sizeof(path), FFMPEG_DUMPDIR"%.16s-%.8s-%d.pcm",
>> link->src->name, link->dst->name, i);
>> + fd = open(path, O_WRONLY | O_CREAT | O_TRUNC, 0644);
>> + if (fd < 0) {
>> + link_uninit_dump_pcm(link, 1);
>> + return AVERROR(errno);
>> + }
>> + link->dump_pcm_fds[i] = fd;
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static int filter_set_dump_pcm(AVFilterContext *filter, const char *target,
>> int set)
>> +{
>> + int i;
>> +
>> + for (i = 0; i < filter->nb_outputs; i++) {
>> + AVFilterLink *link = filter->outputs[i];
>> + if (!target || !strcmp(link->dst->name, target)) {
>> + if (set) {
>> + link->dump_pcm = 1;
>> + } else
>> + link_uninit_dump_pcm(link, 1);
>> +
>> + if (target)
>> + return 0;
>> + }
>> + }
>> +
>> + return target ? AVERROR(EINVAL) : 0;
>> +}
>> +
>> static void link_free(AVFilterLink **link)
>> {
>> FilterLinkInternal *li;
>> @@ -208,6 +271,8 @@ static void link_free(AVFilterLink **link)
>> av_channel_layout_uninit(&(*link)->ch_layout);
>> av_frame_side_data_free(&(*link)->side_data, &(*link)->nb_side_data);
>>
>> + link_uninit_dump_pcm(*link, 1);
>> +
>> av_buffer_unref(&li->l.hw_frames_ctx);
>>
>> av_freep(link);
>> @@ -617,6 +682,10 @@ int avfilter_process_command(AVFilterContext *filter,
>> const char *cmd, const cha
>> if (res == local_res)
>> av_log(filter, AV_LOG_INFO, "%s", res);
>> return 0;
>> + }else if(!strcmp(cmd, "dump_raw_start")) {
>> + return filter_set_dump_pcm(filter, arg, 1);
>> + }else if(!strcmp(cmd, "dump_raw_stop")) {
>> + return filter_set_dump_pcm(filter, arg, 0);
>> }else if(!strcmp(cmd, "enable")) {
>> return set_enable_expr(fffilterctx(filter), arg);
>> }else if (fffilter(filter->filter)->process_command) {
>> @@ -1050,6 +1119,41 @@ fail:
>> return ret;
>> }
>>
>> +static int link_dump_frame(AVFilterLink *link, AVFrame *frame)
>> +{
>> + int samples_size, ret;
>> +
>> + if (!link->dump_pcm_fds) {
>> + ret = link_init_dump_pcm(link);
>> + if (ret < 0)
>> + return ret;
>> + }
>> +
>> + samples_size = av_get_bytes_per_sample(frame->format) *
>> frame->nb_samples;
>> + if (av_sample_fmt_is_planar(frame->format)) {
>> + int i;
>> + for (i = 0; i < link->nb_dump_pcm_fds && i <
>> frame->ch_layout.nb_channels; i++) {
>> + if (i < AV_NUM_DATA_POINTERS) {
>> + ret = write(link->dump_pcm_fds[i], frame->data[i],
>> samples_size);
>> + } else
>> + ret = write(link->dump_pcm_fds[i], frame->extended_data[i -
>> AV_NUM_DATA_POINTERS], samples_size);
>> +
>> + if (ret < 0)
>> + goto err;
>> + }
>> + } else {
>> + ret = write(link->dump_pcm_fds[0], frame->data[0], samples_size *
>> frame->ch_layout.nb_channels);
>> + if (ret < 0)
>> + goto err;
>> +
>> + }
>> +
>> + return 0;
>> +err:
>> + link_uninit_dump_pcm(link, 1);
>> + return AVERROR(errno);
>> +}
>> +
>> int ff_filter_frame(AVFilterLink *link, AVFrame *frame)
>> {
>> FilterLinkInternal * const li = ff_link_internal(link);
>> @@ -1087,6 +1191,12 @@ int ff_filter_frame(AVFilterLink *link, AVFrame
>> *frame)
>> link->time_base);
>> }
>>
>> + if (link->dump_pcm && link->type == AVMEDIA_TYPE_AUDIO) {
>> + ret = link_dump_frame(link, frame);
>> + if (ret < 0)
>> + av_log(link->dst, AV_LOG_ERROR, "Dump pcm files failed with
>> %d\n", ret);
>> + }
>> +
>> li->frame_blocked_in = li->frame_wanted_out = 0;
>> li->l.frame_count_in++;
>> li->l.sample_count_in += frame->nb_samples;
>> diff --git a/libavfilter/avfilter.h b/libavfilter/avfilter.h
>> index a89d3cf658..6d04b9da77 100644
>> --- a/libavfilter/avfilter.h
>> +++ b/libavfilter/avfilter.h
>> @@ -404,6 +404,10 @@ struct AVFilterLink {
>> int sample_rate; ///< samples per second
>> AVChannelLayout ch_layout; ///< channel layout of current buffer (see
>> libavutil/channel_layout.h)
>>
>> + int dump_pcm; ///< flag to dump pcm
>> + int *dump_pcm_fds; ///< dump files
>> + unsigned nb_dump_pcm_fds; ///< number of dump file
>> +
>> /**
>> * Define the time base used by the PTS of the frames/samples
>> * which will pass through this link.
>> --
>> 2.34.1
>>
>
> Can't you use the asplit filter to duplicate the audio?
>
> - Andreas
Ping for that question.
- Andreas
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