[FFmpeg-cvslog] lavfi: add video buffer sink, and use it in avtools
Anton Khirnov
git at videolan.org
Thu May 10 02:33:18 CEST 2012
ffmpeg | branch: master | Anton Khirnov <anton at khirnov.net> | Fri Apr 27 06:56:56 2012 +0200| [ac71230902af1a8ebc7abf85143139ffb49838eb] | committer: Anton Khirnov
lavfi: add video buffer sink, and use it in avtools
Also add the public interface libavfilter/buffersink.h.
Based on a commit by Stefano Sabatini.
> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=ac71230902af1a8ebc7abf85143139ffb49838eb
---
avconv.c | 104 ++++++++++++++++++++++++++++++------------
avplay.c | 29 ++++++++---
cmdutils.c | 68 ---------------------------
cmdutils.h | 15 ------
configure | 2 +-
doc/filters.texi | 8 +++
libavfilter/Makefile | 2 +
libavfilter/allfilters.c | 4 ++
libavfilter/buffersink.c | 114 ++++++++++++++++++++++++++++++++++++++++++++++
libavfilter/buffersink.h | 43 +++++++++++++++++
10 files changed, 267 insertions(+), 122 deletions(-)
diff --git a/avconv.c b/avconv.c
index 73f3bc3..33758c1 100644
--- a/avconv.c
+++ b/avconv.c
@@ -50,6 +50,7 @@
# include "libavfilter/avfilter.h"
# include "libavfilter/avfiltergraph.h"
# include "libavfilter/buffersrc.h"
+# include "libavfilter/buffersink.h"
# include "libavfilter/vsrc_buffer.h"
#if HAVE_SYS_RESOURCE_H
@@ -582,14 +583,25 @@ static void filter_release_buffer(AVFilterBuffer *fb)
unref_buffer(buf->ist, buf);
}
-static const enum PixelFormat *choose_pixel_fmts(OutputStream *ost)
+static char *choose_pixel_fmts(OutputStream *ost)
{
if (ost->st->codec->pix_fmt != PIX_FMT_NONE) {
- ost->pix_fmts[0] = ost->st->codec->pix_fmt;
- return ost->pix_fmts;
- } else if (ost->enc->pix_fmts)
- return ost->enc->pix_fmts;
- else
+ return av_strdup(av_get_pix_fmt_name(ost->st->codec->pix_fmt));
+ } else if (ost->enc->pix_fmts) {
+ const enum PixelFormat *p;
+ AVIOContext *s = NULL;
+ uint8_t *ret;
+ int len;
+
+ if (avio_open_dyn_buf(&s) < 0)
+ exit_program(1);
+
+ for (p = ost->enc->pix_fmts; *p != PIX_FMT_NONE; p++)
+ avio_printf(s, "%s:", av_get_pix_fmt_name(*p));
+ len = avio_close_dyn_buf(s, &ret);
+ ret[len - 1] = 0;
+ return ret;
+ } else
return NULL;
}
@@ -597,9 +609,9 @@ static int configure_video_filters(FilterGraph *fg)
{
InputStream *ist = fg->inputs[0]->ist;
OutputStream *ost = fg->outputs[0]->ost;
- AVFilterContext *last_filter, *filter;
+ AVFilterContext *in_filter, *out_filter, *filter;
AVCodecContext *codec = ost->st->codec;
- SinkContext sink_ctx = { .pix_fmts = choose_pixel_fmts(ost) };
+ char *pix_fmts;
AVRational sample_aspect_ratio;
char args[255];
int ret;
@@ -621,11 +633,13 @@ static int configure_video_filters(FilterGraph *fg)
"src", args, NULL, fg->graph);
if (ret < 0)
return ret;
- ret = avfilter_graph_create_filter(&fg->outputs[0]->filter, &sink,
- "out", NULL, &sink_ctx, fg->graph);
+ ret = avfilter_graph_create_filter(&fg->outputs[0]->filter,
+ avfilter_get_by_name("buffersink"),
+ "out", NULL, NULL, fg->graph);
if (ret < 0)
return ret;
- last_filter = fg->inputs[0]->filter;
+ in_filter = fg->inputs[0]->filter;
+ out_filter = fg->outputs[0]->filter;
if (codec->width || codec->height) {
snprintf(args, 255, "%d:%d:flags=0x%X",
@@ -635,9 +649,22 @@ static int configure_video_filters(FilterGraph *fg)
if ((ret = avfilter_graph_create_filter(&filter, avfilter_get_by_name("scale"),
NULL, args, NULL, fg->graph)) < 0)
return ret;
- if ((ret = avfilter_link(last_filter, 0, filter, 0)) < 0)
+ if ((ret = avfilter_link(in_filter, 0, filter, 0)) < 0)
return ret;
- last_filter = filter;
+ in_filter = filter;
+ }
+
+ if ((pix_fmts = choose_pixel_fmts(ost))) {
+ if ((ret = avfilter_graph_create_filter(&filter,
+ avfilter_get_by_name("format"),
+ "format", pix_fmts, NULL,
+ fg->graph)) < 0)
+ return ret;
+ if ((ret = avfilter_link(filter, 0, out_filter, 0)) < 0)
+ return ret;
+
+ out_filter = filter;
+ av_freep(&pix_fmts);
}
snprintf(args, sizeof(args), "flags=0x%X", (unsigned)ost->sws_flags);
@@ -648,19 +675,19 @@ static int configure_video_filters(FilterGraph *fg)
AVFilterInOut *inputs = avfilter_inout_alloc();
outputs->name = av_strdup("in");
- outputs->filter_ctx = last_filter;
+ outputs->filter_ctx = in_filter;
outputs->pad_idx = 0;
outputs->next = NULL;
inputs->name = av_strdup("out");
- inputs->filter_ctx = fg->outputs[0]->filter;
+ inputs->filter_ctx = out_filter;
inputs->pad_idx = 0;
inputs->next = NULL;
if ((ret = avfilter_graph_parse(fg->graph, ost->avfilter, inputs, outputs, NULL)) < 0)
return ret;
} else {
- if ((ret = avfilter_link(last_filter, 0, fg->outputs[0]->filter, 0)) < 0)
+ if ((ret = avfilter_link(in_filter, 0, out_filter, 0)) < 0)
return ret;
}
@@ -776,33 +803,52 @@ static void init_input_filter(FilterGraph *fg, AVFilterInOut *in)
static int configure_output_filter(FilterGraph *fg, OutputFilter *ofilter, AVFilterInOut *out)
{
- SinkContext sink_ctx;
+ char *pix_fmts;
AVCodecContext *codec = ofilter->ost->st->codec;
AVFilterContext *last_filter = out->filter_ctx;
int pad_idx = out->pad_idx;
int ret;
- sink_ctx.pix_fmts = choose_pixel_fmts(ofilter->ost);
- ret = avfilter_graph_create_filter(&ofilter->filter, &sink,
- "out", NULL, &sink_ctx, fg->graph);
+ ret = avfilter_graph_create_filter(&ofilter->filter,
+ avfilter_get_by_name("buffersink"),
+ "out", NULL, pix_fmts, fg->graph);
if (ret < 0)
return ret;
if (codec->width || codec->height) {
char args[255];
+ AVFilterContext *filter;
+
snprintf(args, sizeof(args), "%d:%d:flags=0x%X",
codec->width,
codec->height,
(unsigned)ofilter->ost->sws_flags);
- if ((ret = avfilter_graph_create_filter(&last_filter, avfilter_get_by_name("scale"),
+ if ((ret = avfilter_graph_create_filter(&filter, avfilter_get_by_name("scale"),
NULL, args, NULL, fg->graph)) < 0)
return ret;
- if ((ret = avfilter_link(out->filter_ctx, out->pad_idx, last_filter, 0)) < 0)
+ if ((ret = avfilter_link(last_filter, pad_idx, filter, 0)) < 0)
return ret;
+
+ last_filter = filter;
pad_idx = 0;
}
+ if ((pix_fmts = choose_pixel_fmts(ofilter->ost))) {
+ AVFilterContext *filter;
+ if ((ret = avfilter_graph_create_filter(&filter,
+ avfilter_get_by_name("format"),
+ "format", pix_fmts, NULL,
+ fg->graph)) < 0)
+ return ret;
+ if ((ret = avfilter_link(last_filter, pad_idx, filter, 0)) < 0)
+ return ret;
+
+ last_filter = filter;
+ pad_idx = 0;
+ av_freep(&pix_fmts);
+ }
+
if ((ret = avfilter_link(last_filter, pad_idx, ofilter->filter, 0)) < 0)
return ret;
@@ -1801,7 +1847,7 @@ static int poll_filters(void)
{
AVFilterBufferRef *picref;
AVFrame *filtered_frame = NULL;
- int i, frame_size, ret;
+ int i, frame_size;
for (i = 0; i < nb_output_streams; i++) {
OutputStream *ost = output_streams[i];
@@ -1816,13 +1862,11 @@ static int poll_filters(void)
avcodec_get_frame_defaults(ost->filtered_frame);
filtered_frame = ost->filtered_frame;
- while (avfilter_poll_frame(ost->filter->filter->inputs[0])) {
- AVRational ist_pts_tb;
- if ((ret = get_filtered_video_frame(ost->filter->filter,
- filtered_frame, &picref,
- &ist_pts_tb)) < 0)
- return ret;
- filtered_frame->pts = av_rescale_q(picref->pts, ist_pts_tb, AV_TIME_BASE_Q);
+ while (av_buffersink_read(ost->filter->filter, &picref) >= 0) {
+ avfilter_copy_buf_props(filtered_frame, picref);
+ filtered_frame->pts = av_rescale_q(picref->pts,
+ ost->filter->filter->inputs[0]->time_base,
+ AV_TIME_BASE_Q);
if (of->start_time && filtered_frame->pts < of->start_time)
return 0;
diff --git a/avplay.c b/avplay.c
index 9bd83f3..d291ba3 100644
--- a/avplay.c
+++ b/avplay.c
@@ -41,6 +41,7 @@
#if CONFIG_AVFILTER
# include "libavfilter/avfilter.h"
# include "libavfilter/avfiltergraph.h"
+# include "libavfilter/buffersink.h"
#endif
#include "cmdutils.h"
@@ -1708,21 +1709,28 @@ static AVFilter input_filter =
static int configure_video_filters(AVFilterGraph *graph, VideoState *is, const char *vfilters)
{
- static const enum PixelFormat pix_fmts[] = { PIX_FMT_YUV420P, PIX_FMT_NONE };
char sws_flags_str[128];
int ret;
- SinkContext sink_ctx = { .pix_fmts = pix_fmts };
- AVFilterContext *filt_src = NULL, *filt_out = NULL;
+ AVFilterContext *filt_src = NULL, *filt_out = NULL, *filt_format;
snprintf(sws_flags_str, sizeof(sws_flags_str), "flags=%d", sws_flags);
graph->scale_sws_opts = av_strdup(sws_flags_str);
if ((ret = avfilter_graph_create_filter(&filt_src, &input_filter, "src",
NULL, is, graph)) < 0)
return ret;
- if ((ret = avfilter_graph_create_filter(&filt_out, &sink, "out",
- NULL, &sink_ctx, graph)) < 0)
+ if ((ret = avfilter_graph_create_filter(&filt_out,
+ avfilter_get_by_name("buffersink"),
+ "out", NULL, NULL, graph)) < 0)
return ret;
+ if ((ret = avfilter_graph_create_filter(&filt_format,
+ avfilter_get_by_name("format"),
+ "format", "yuv420p", NULL, graph)) < 0)
+ return ret;
+ if ((ret = avfilter_link(filt_format, 0, filt_out, 0)) < 0)
+ return ret;
+
+
if (vfilters) {
AVFilterInOut *outputs = avfilter_inout_alloc();
AVFilterInOut *inputs = avfilter_inout_alloc();
@@ -1733,14 +1741,14 @@ static int configure_video_filters(AVFilterGraph *graph, VideoState *is, const c
outputs->next = NULL;
inputs->name = av_strdup("out");
- inputs->filter_ctx = filt_out;
+ inputs->filter_ctx = filt_format;
inputs->pad_idx = 0;
inputs->next = NULL;
if ((ret = avfilter_graph_parse(graph, vfilters, inputs, outputs, NULL)) < 0)
return ret;
} else {
- if ((ret = avfilter_link(filt_src, 0, filt_out, 0)) < 0)
+ if ((ret = avfilter_link(filt_src, 0, filt_format, 0)) < 0)
return ret;
}
@@ -1796,11 +1804,16 @@ static int video_thread(void *arg)
last_w = is->video_st->codec->width;
last_h = is->video_st->codec->height;
}
- ret = get_filtered_video_frame(filt_out, frame, &picref, &tb);
+ ret = av_buffersink_read(filt_out, &picref);
if (picref) {
+ avfilter_copy_buf_props(frame, picref);
+
pts_int = picref->pts;
+ tb = filt_out->inputs[0]->time_base;
pos = picref->pos;
frame->opaque = picref;
+
+ ret = 1;
}
if (ret >= 0 && av_cmp_q(tb, is->video_st->time_base)) {
diff --git a/cmdutils.c b/cmdutils.c
index 6d2e97f..3cd11ca 100644
--- a/cmdutils.c
+++ b/cmdutils.c
@@ -1021,74 +1021,6 @@ AVDictionary **setup_find_stream_info_opts(AVFormatContext *s,
return opts;
}
-#if CONFIG_AVFILTER
-
-static int sink_init(AVFilterContext *ctx, const char *args, void *opaque)
-{
- SinkContext *priv = ctx->priv;
-
- if (!opaque)
- return AVERROR(EINVAL);
- *priv = *(SinkContext *)opaque;
-
- return 0;
-}
-
-static void null_end_frame(AVFilterLink *inlink) { }
-
-static int sink_query_formats(AVFilterContext *ctx)
-{
- SinkContext *priv = ctx->priv;
-
- if (priv->pix_fmts)
- avfilter_set_common_formats(ctx, avfilter_make_format_list(priv->pix_fmts));
- else
- avfilter_default_query_formats(ctx);
- return 0;
-}
-
-AVFilter sink = {
- .name = "sink",
- .priv_size = sizeof(SinkContext),
- .init = sink_init,
-
- .query_formats = sink_query_formats,
-
- .inputs = (AVFilterPad[]) {{ .name = "default",
- .type = AVMEDIA_TYPE_VIDEO,
- .end_frame = null_end_frame,
- .min_perms = AV_PERM_READ, },
- { .name = NULL }},
- .outputs = (AVFilterPad[]) {{ .name = NULL }},
-};
-
-int get_filtered_video_frame(AVFilterContext *ctx, AVFrame *frame,
- AVFilterBufferRef **picref_ptr, AVRational *tb)
-{
- int ret;
- AVFilterBufferRef *picref;
-
- if ((ret = avfilter_request_frame(ctx->inputs[0])) < 0)
- return ret;
- if (!(picref = ctx->inputs[0]->cur_buf))
- return AVERROR(ENOENT);
- *picref_ptr = picref;
- ctx->inputs[0]->cur_buf = NULL;
- *tb = ctx->inputs[0]->time_base;
-
- memcpy(frame->data, picref->data, sizeof(frame->data));
- memcpy(frame->linesize, picref->linesize, sizeof(frame->linesize));
- frame->interlaced_frame = picref->video->interlaced;
- frame->top_field_first = picref->video->top_field_first;
- frame->key_frame = picref->video->key_frame;
- frame->pict_type = picref->video->pict_type;
- frame->sample_aspect_ratio = picref->video->pixel_aspect;
-
- return 1;
-}
-
-#endif /* CONFIG_AVFILTER */
-
void *grow_array(void *array, int elem_size, int *size, int new_size)
{
if (new_size >= INT_MAX / elem_size) {
diff --git a/cmdutils.h b/cmdutils.h
index 792254c..6fff47d 100644
--- a/cmdutils.h
+++ b/cmdutils.h
@@ -367,21 +367,6 @@ int64_t guess_correct_pts(PtsCorrectionContext *ctx, int64_t pts, int64_t dts);
FILE *get_preset_file(char *filename, size_t filename_size,
const char *preset_name, int is_path, const char *codec_name);
-typedef struct {
- const enum PixelFormat *pix_fmts;
-} SinkContext;
-
-extern AVFilter sink;
-
-/**
- * Extract a frame from sink.
- *
- * @return a negative error in case of failure, 1 if one frame has
- * been extracted successfully.
- */
-int get_filtered_video_frame(AVFilterContext *sink, AVFrame *frame,
- AVFilterBufferRef **picref, AVRational *pts_tb);
-
/**
* Do all the necessary cleanup and abort.
* This function is implemented in the avtools, not cmdutils.
diff --git a/configure b/configure
index 67cba5a..4b1e551 100755
--- a/configure
+++ b/configure
@@ -1540,7 +1540,7 @@ avfilter_deps="swscale"
avformat_deps="avcodec"
# programs
-avconv_deps="avcodec avfilter avformat avresample swscale"
+avconv_deps="avcodec avfilter avformat avresample swscale format_filter"
avplay_deps="avcodec avformat swscale sdl"
avplay_select="rdft"
avprobe_deps="avcodec avformat"
diff --git a/doc/filters.texi b/doc/filters.texi
index c5a56f4..dbcc86a 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -2078,6 +2078,14 @@ will generate a video with a duration of 5.3 seconds, with size
Below is a description of the currently available video sinks.
+ at section buffersink
+
+Buffer video frames, and make them available to the end of the filter
+graph.
+
+This sink is intended for a programmatic use through the interface defined in
+ at file{libavfilter/buffersink.h}.
+
@section nullsink
Null video sink, do absolutely nothing with the input video. It is
diff --git a/libavfilter/Makefile b/libavfilter/Makefile
index ae85839..e786b6d 100644
--- a/libavfilter/Makefile
+++ b/libavfilter/Makefile
@@ -4,6 +4,7 @@ FFLIBS-$(CONFIG_MOVIE_FILTER) += avformat avcodec
HEADERS = avfilter.h \
avfiltergraph.h \
+ buffersink.h \
buffersrc.h \
version.h \
vsrc_buffer.h \
@@ -11,6 +12,7 @@ HEADERS = avfilter.h \
OBJS = allfilters.o \
avfilter.o \
avfiltergraph.o \
+ buffersink.o \
defaults.o \
drawutils.o \
formats.o \
diff --git a/libavfilter/allfilters.c b/libavfilter/allfilters.c
index 198e152..f887002 100644
--- a/libavfilter/allfilters.c
+++ b/libavfilter/allfilters.c
@@ -95,6 +95,10 @@ void avfilter_register_all(void)
avfilter_register(&avfilter_vsrc_buffer);
}
{
+ extern AVFilter avfilter_vsink_buffer;
+ avfilter_register(&avfilter_vsink_buffer);
+ }
+ {
extern AVFilter avfilter_vf_scale;
avfilter_register(&avfilter_vf_scale);
}
diff --git a/libavfilter/buffersink.c b/libavfilter/buffersink.c
new file mode 100644
index 0000000..e4cbe3b
--- /dev/null
+++ b/libavfilter/buffersink.c
@@ -0,0 +1,114 @@
+/*
+ * Copyright (c) 2011 Stefano Sabatini
+ *
+ * This file is part of Libav.
+ *
+ * Libav 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.
+ *
+ * Libav 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 Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file
+ * buffer sink
+ */
+
+#include "libavutil/fifo.h"
+
+#include "avfilter.h"
+#include "buffersink.h"
+
+typedef struct {
+ AVFifoBuffer *fifo; ///< FIFO buffer of video frame references
+} BufferSinkContext;
+
+#define FIFO_INIT_SIZE 8
+
+static av_cold void uninit(AVFilterContext *ctx)
+{
+ BufferSinkContext *sink = ctx->priv;
+
+ while (sink->fifo && av_fifo_size(sink->fifo)) {
+ AVFilterBufferRef *buf;
+ av_fifo_generic_read(sink->fifo, &buf, sizeof(buf), NULL);
+ avfilter_unref_buffer(buf);
+ }
+ av_fifo_free(sink->fifo);
+}
+
+static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
+{
+ BufferSinkContext *sink = ctx->priv;
+
+ if (!(sink->fifo = av_fifo_alloc(FIFO_INIT_SIZE*sizeof(AVFilterBufferRef*)))) {
+ av_log(ctx, AV_LOG_ERROR, "Failed to allocate fifo\n");
+ return AVERROR(ENOMEM);
+ }
+
+ return 0;
+}
+
+static void end_frame(AVFilterLink *link)
+{
+ AVFilterContext *ctx = link->dst;
+ BufferSinkContext *sink = ctx->priv;
+
+ if (av_fifo_space(sink->fifo) < sizeof(AVFilterBufferRef *) &&
+ (av_fifo_realloc2(sink->fifo, av_fifo_size(sink->fifo) * 2) < 0)) {
+ av_log(ctx, AV_LOG_ERROR, "Error reallocating the FIFO.\n");
+ return;
+ }
+
+ av_fifo_generic_write(sink->fifo, &link->cur_buf, sizeof(link->cur_buf), NULL);
+ link->cur_buf = NULL;
+}
+
+int av_buffersink_read(AVFilterContext *ctx, AVFilterBufferRef **buf)
+{
+ BufferSinkContext *sink = ctx->priv;
+ AVFilterLink *link = ctx->inputs[0];
+ int ret;
+
+ if (!buf) {
+ if (av_fifo_size(sink->fifo))
+ return av_fifo_size(sink->fifo)/sizeof(*buf);
+ else
+ return avfilter_poll_frame(ctx->inputs[0]);
+ }
+
+ if (!av_fifo_size(sink->fifo) &&
+ (ret = avfilter_request_frame(link)) < 0)
+ return ret;
+
+ if (!av_fifo_size(sink->fifo))
+ return AVERROR(EINVAL);
+
+ av_fifo_generic_read(sink->fifo, buf, sizeof(*buf), NULL);
+
+ return 0;
+}
+
+AVFilter avfilter_vsink_buffer = {
+ .name = "buffersink",
+ .description = NULL_IF_CONFIG_SMALL("Buffer video frames, and make them available to the end of the filter graph."),
+ .priv_size = sizeof(BufferSinkContext),
+ .init = init,
+ .uninit = uninit,
+
+ .inputs = (AVFilterPad[]) {{ .name = "default",
+ .type = AVMEDIA_TYPE_VIDEO,
+ .end_frame = end_frame,
+ .min_perms = AV_PERM_READ, },
+ { .name = NULL }},
+ .outputs = (AVFilterPad[]) {{ .name = NULL }},
+};
diff --git a/libavfilter/buffersink.h b/libavfilter/buffersink.h
new file mode 100644
index 0000000..e579b9a
--- /dev/null
+++ b/libavfilter/buffersink.h
@@ -0,0 +1,43 @@
+/*
+ * This file is part of Libav.
+ *
+ * Libav 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.
+ *
+ * Libav 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 Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AVFILTER_BUFFERSINK_H
+#define AVFILTER_BUFFERSINK_H
+
+/**
+ * @file
+ * memory buffer sink API
+ */
+
+#include "avfilter.h"
+
+/**
+ * Get a buffer with filtered data from sink and put it in buf.
+ *
+ * @param sink pointer to a context of a buffersink AVFilter.
+ * @param buf pointer to the buffer will be written here if buf is non-NULL. buf
+ * must be freed by the caller using avfilter_unref_buffer().
+ * Buf may also be NULL to query whether a buffer is ready to be
+ * output.
+ *
+ * @return >= 0 in case of success, a negative AVERROR code in case of
+ * failure.
+ */
+int av_buffersink_read(AVFilterContext *sink, AVFilterBufferRef **buf);
+
+#endif /* AVFILTER_BUFFERSINK_H */
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