FFmpeg
filtering_audio.c
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1 /*
2  * Copyright (c) 2010 Nicolas George
3  * Copyright (c) 2011 Stefano Sabatini
4  * Copyright (c) 2012 Clément Bœsch
5  *
6  * Permission is hereby granted, free of charge, to any person obtaining a copy
7  * of this software and associated documentation files (the "Software"), to deal
8  * in the Software without restriction, including without limitation the rights
9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
10  * copies of the Software, and to permit persons to whom the Software is
11  * furnished to do so, subject to the following conditions:
12  *
13  * The above copyright notice and this permission notice shall be included in
14  * all copies or substantial portions of the Software.
15  *
16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
22  * THE SOFTWARE.
23  */
24 
25 /**
26  * @file
27  * API example for audio decoding and filtering
28  * @example filtering_audio.c
29  */
30 
31 #include <unistd.h>
32 
33 #include <libavcodec/avcodec.h>
34 #include <libavformat/avformat.h>
35 #include <libavfilter/buffersink.h>
36 #include <libavfilter/buffersrc.h>
38 #include <libavutil/opt.h>
39 
40 static const char *filter_descr = "aresample=8000,aformat=sample_fmts=s16:channel_layouts=mono";
41 static const char *player = "ffplay -f s16le -ar 8000 -ac 1 -";
42 
48 static int audio_stream_index = -1;
49 
50 static int open_input_file(const char *filename)
51 {
52  const AVCodec *dec;
53  int ret;
54 
55  if ((ret = avformat_open_input(&fmt_ctx, filename, NULL, NULL)) < 0) {
56  av_log(NULL, AV_LOG_ERROR, "Cannot open input file\n");
57  return ret;
58  }
59 
60  if ((ret = avformat_find_stream_info(fmt_ctx, NULL)) < 0) {
61  av_log(NULL, AV_LOG_ERROR, "Cannot find stream information\n");
62  return ret;
63  }
64 
65  /* select the audio stream */
67  if (ret < 0) {
68  av_log(NULL, AV_LOG_ERROR, "Cannot find an audio stream in the input file\n");
69  return ret;
70  }
72 
73  /* create decoding context */
75  if (!dec_ctx)
76  return AVERROR(ENOMEM);
78 
79  /* init the audio decoder */
80  if ((ret = avcodec_open2(dec_ctx, dec, NULL)) < 0) {
81  av_log(NULL, AV_LOG_ERROR, "Cannot open audio decoder\n");
82  return ret;
83  }
84 
85  return 0;
86 }
87 
88 static int init_filters(const char *filters_descr)
89 {
90  char args[512];
91  int ret = 0;
92  const AVFilter *abuffersrc = avfilter_get_by_name("abuffer");
93  const AVFilter *abuffersink = avfilter_get_by_name("abuffersink");
96  static const enum AVSampleFormat out_sample_fmts[] = { AV_SAMPLE_FMT_S16, -1 };
97  static const int out_sample_rates[] = { 8000, -1 };
98  const AVFilterLink *outlink;
100 
102  if (!outputs || !inputs || !filter_graph) {
103  ret = AVERROR(ENOMEM);
104  goto end;
105  }
106 
107  /* buffer audio source: the decoded frames from the decoder will be inserted here. */
110  ret = snprintf(args, sizeof(args),
111  "time_base=%d/%d:sample_rate=%d:sample_fmt=%s:channel_layout=",
112  time_base.num, time_base.den, dec_ctx->sample_rate,
114  av_channel_layout_describe(&dec_ctx->ch_layout, args + ret, sizeof(args) - ret);
115  ret = avfilter_graph_create_filter(&buffersrc_ctx, abuffersrc, "in",
116  args, NULL, filter_graph);
117  if (ret < 0) {
118  av_log(NULL, AV_LOG_ERROR, "Cannot create audio buffer source\n");
119  goto end;
120  }
121 
122  /* buffer audio sink: to terminate the filter chain. */
123  ret = avfilter_graph_create_filter(&buffersink_ctx, abuffersink, "out",
125  if (ret < 0) {
126  av_log(NULL, AV_LOG_ERROR, "Cannot create audio buffer sink\n");
127  goto end;
128  }
129 
130  ret = av_opt_set_int_list(buffersink_ctx, "sample_fmts", out_sample_fmts, -1,
132  if (ret < 0) {
133  av_log(NULL, AV_LOG_ERROR, "Cannot set output sample format\n");
134  goto end;
135  }
136 
137  ret = av_opt_set(buffersink_ctx, "ch_layouts", "mono",
139  if (ret < 0) {
140  av_log(NULL, AV_LOG_ERROR, "Cannot set output channel layout\n");
141  goto end;
142  }
143 
144  ret = av_opt_set_int_list(buffersink_ctx, "sample_rates", out_sample_rates, -1,
146  if (ret < 0) {
147  av_log(NULL, AV_LOG_ERROR, "Cannot set output sample rate\n");
148  goto end;
149  }
150 
151  /*
152  * Set the endpoints for the filter graph. The filter_graph will
153  * be linked to the graph described by filters_descr.
154  */
155 
156  /*
157  * The buffer source output must be connected to the input pad of
158  * the first filter described by filters_descr; since the first
159  * filter input label is not specified, it is set to "in" by
160  * default.
161  */
162  outputs->name = av_strdup("in");
163  outputs->filter_ctx = buffersrc_ctx;
164  outputs->pad_idx = 0;
165  outputs->next = NULL;
166 
167  /*
168  * The buffer sink input must be connected to the output pad of
169  * the last filter described by filters_descr; since the last
170  * filter output label is not specified, it is set to "out" by
171  * default.
172  */
173  inputs->name = av_strdup("out");
174  inputs->filter_ctx = buffersink_ctx;
175  inputs->pad_idx = 0;
176  inputs->next = NULL;
177 
178  if ((ret = avfilter_graph_parse_ptr(filter_graph, filters_descr,
179  &inputs, &outputs, NULL)) < 0)
180  goto end;
181 
183  goto end;
184 
185  /* Print summary of the sink buffer
186  * Note: args buffer is reused to store channel layout string */
187  outlink = buffersink_ctx->inputs[0];
188  av_channel_layout_describe(&outlink->ch_layout, args, sizeof(args));
189  av_log(NULL, AV_LOG_INFO, "Output: srate:%dHz fmt:%s chlayout:%s\n",
190  (int)outlink->sample_rate,
191  (char *)av_x_if_null(av_get_sample_fmt_name(outlink->format), "?"),
192  args);
193 
194 end:
197 
198  return ret;
199 }
200 
201 static void print_frame(const AVFrame *frame)
202 {
203  const int n = frame->nb_samples * frame->ch_layout.nb_channels;
204  const uint16_t *p = (uint16_t*)frame->data[0];
205  const uint16_t *p_end = p + n;
206 
207  while (p < p_end) {
208  fputc(*p & 0xff, stdout);
209  fputc(*p>>8 & 0xff, stdout);
210  p++;
211  }
212  fflush(stdout);
213 }
214 
215 int main(int argc, char **argv)
216 {
217  int ret;
218  AVPacket *packet = av_packet_alloc();
220  AVFrame *filt_frame = av_frame_alloc();
221 
222  if (!packet || !frame || !filt_frame) {
223  fprintf(stderr, "Could not allocate frame or packet\n");
224  exit(1);
225  }
226  if (argc != 2) {
227  fprintf(stderr, "Usage: %s file | %s\n", argv[0], player);
228  exit(1);
229  }
230 
231  if ((ret = open_input_file(argv[1])) < 0)
232  goto end;
233  if ((ret = init_filters(filter_descr)) < 0)
234  goto end;
235 
236  /* read all packets */
237  while (1) {
238  if ((ret = av_read_frame(fmt_ctx, packet)) < 0)
239  break;
240 
241  if (packet->stream_index == audio_stream_index) {
242  ret = avcodec_send_packet(dec_ctx, packet);
243  if (ret < 0) {
244  av_log(NULL, AV_LOG_ERROR, "Error while sending a packet to the decoder\n");
245  break;
246  }
247 
248  while (ret >= 0) {
250  if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
251  break;
252  } else if (ret < 0) {
253  av_log(NULL, AV_LOG_ERROR, "Error while receiving a frame from the decoder\n");
254  goto end;
255  }
256 
257  if (ret >= 0) {
258  /* push the audio data from decoded frame into the filtergraph */
260  av_log(NULL, AV_LOG_ERROR, "Error while feeding the audio filtergraph\n");
261  break;
262  }
263 
264  /* pull filtered audio from the filtergraph */
265  while (1) {
267  if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
268  break;
269  if (ret < 0)
270  goto end;
271  print_frame(filt_frame);
272  av_frame_unref(filt_frame);
273  }
275  }
276  }
277  }
278  av_packet_unref(packet);
279  }
280 end:
284  av_packet_free(&packet);
286  av_frame_free(&filt_frame);
287 
288  if (ret < 0 && ret != AVERROR_EOF) {
289  fprintf(stderr, "Error occurred: %s\n", av_err2str(ret));
290  exit(1);
291  }
292 
293  exit(0);
294 }
av_packet_unref
void av_packet_unref(AVPacket *pkt)
Wipe the packet.
Definition: avpacket.c:422
AVCodec
AVCodec.
Definition: codec.h:184
AVERROR
Filter the word “frame” indicates either a video frame or a group of audio as stored in an AVFrame structure Format for each input and each output the list of supported formats For video that means pixel format For audio that means channel sample they are references to shared objects When the negotiation mechanism computes the intersection of the formats supported at each end of a all references to both lists are replaced with a reference to the intersection And when a single format is eventually chosen for a link amongst the remaining all references to the list are updated That means that if a filter requires that its input and output have the same format amongst a supported all it has to do is use a reference to the same list of formats query_formats can leave some formats unset and return AVERROR(EAGAIN) to cause the negotiation mechanism toagain later. That can be used by filters with complex requirements to use the format negotiated on one link to set the formats supported on another. Frame references ownership and permissions
opt.h
AVCodecContext::sample_rate
int sample_rate
samples per second
Definition: avcodec.h:1034
AVERROR_EOF
#define AVERROR_EOF
End of file.
Definition: error.h:57
buffersink_ctx
AVFilterContext * buffersink_ctx
Definition: filtering_audio.c:45
av_opt_set_int_list
#define av_opt_set_int_list(obj, name, val, term, flags)
Set a binary option to an integer list.
Definition: opt.h:721
AV_BUFFERSRC_FLAG_KEEP_REF
@ AV_BUFFERSRC_FLAG_KEEP_REF
Keep a reference to the frame.
Definition: buffersrc.h:53
av_frame_free
void av_frame_free(AVFrame **frame)
Free the frame and any dynamically allocated objects in it, e.g.
Definition: frame.c:99
AVFrame
This structure describes decoded (raw) audio or video data.
Definition: frame.h:330
AVFormatContext::streams
AVStream ** streams
A list of all streams in the file.
Definition: avformat.h:1172
AVChannelLayout::order
enum AVChannelOrder order
Channel order used in this layout.
Definition: channel_layout.h:306
av_read_frame
int av_read_frame(AVFormatContext *s, AVPacket *pkt)
Return the next frame of a stream.
Definition: demux.c:1439
AVChannelLayout::nb_channels
int nb_channels
Number of channels in this layout.
Definition: channel_layout.h:311
av_packet_free
void av_packet_free(AVPacket **pkt)
Free the packet, if the packet is reference counted, it will be unreferenced first.
Definition: avpacket.c:73
avfilter_graph_free
void avfilter_graph_free(AVFilterGraph **graph)
Free a graph, destroy its links, and set *graph to NULL.
Definition: avfiltergraph.c:119
av_find_best_stream
int av_find_best_stream(AVFormatContext *ic, enum AVMediaType type, int wanted_stream_nb, int related_stream, const AVCodec **decoder_ret, int flags)
Find the "best" stream in the file.
Definition: avformat.c:414
avformat_close_input
void avformat_close_input(AVFormatContext **s)
Close an opened input AVFormatContext.
Definition: demux.c:369
avfilter_graph_create_filter
int avfilter_graph_create_filter(AVFilterContext **filt_ctx, const AVFilter *filt, const char *name, const char *args, void *opaque, AVFilterGraph *graph_ctx)
Create and add a filter instance into an existing graph.
Definition: avfiltergraph.c:138
AVCodecContext::ch_layout
AVChannelLayout ch_layout
Audio channel layout.
Definition: avcodec.h:2050
filter_graph
AVFilterGraph * filter_graph
Definition: filtering_audio.c:47
avfilter_graph_alloc
AVFilterGraph * avfilter_graph_alloc(void)
Allocate a filter graph.
Definition: avfiltergraph.c:82
av_opt_set
int av_opt_set(void *obj, const char *name, const char *val, int search_flags)
Definition: opt.c:487
AVRational::num
int num
Numerator.
Definition: rational.h:59
main
int main(int argc, char **argv)
Definition: filtering_audio.c:215
av_frame_alloc
AVFrame * av_frame_alloc(void)
Allocate an AVFrame and set its fields to default values.
Definition: frame.c:87
avfilter_inout_free
void avfilter_inout_free(AVFilterInOut **inout)
Free the supplied list of AVFilterInOut and set *inout to NULL.
Definition: graphparser.c:206
player
static const char * player
Definition: filtering_audio.c:41
AV_LOG_ERROR
#define AV_LOG_ERROR
Something went wrong and cannot losslessly be recovered.
Definition: log.h:180
open_input_file
static int open_input_file(const char *filename)
Definition: filtering_audio.c:50
avformat_open_input
int avformat_open_input(AVFormatContext **ps, const char *url, const AVInputFormat *fmt, AVDictionary **options)
Open an input stream and read the header.
Definition: demux.c:221
av_channel_layout_describe
int av_channel_layout_describe(const AVChannelLayout *channel_layout, char *buf, size_t buf_size)
Get a human-readable string describing the channel layout properties.
Definition: channel_layout.c:778
avcodec_alloc_context3
AVCodecContext * avcodec_alloc_context3(const AVCodec *codec)
Allocate an AVCodecContext and set its fields to default values.
Definition: options.c:153
AVMEDIA_TYPE_AUDIO
@ AVMEDIA_TYPE_AUDIO
Definition: avutil.h:202
AV_CHANNEL_ORDER_UNSPEC
@ AV_CHANNEL_ORDER_UNSPEC
Only the channel count is specified, without any further information about the channel order.
Definition: channel_layout.h:112
av_buffersink_get_frame
int attribute_align_arg av_buffersink_get_frame(AVFilterContext *ctx, AVFrame *frame)
Get a frame with filtered data from sink and put it in frame.
Definition: buffersink.c:94
avcodec_receive_frame
int attribute_align_arg avcodec_receive_frame(AVCodecContext *avctx, AVFrame *frame)
Return decoded output data from a decoder or encoder (when the AV_CODEC_FLAG_RECON_FRAME flag is used...
Definition: avcodec.c:704
outputs
static const AVFilterPad outputs[]
Definition: af_acontrast.c:172
init_filters
static int init_filters(const char *filters_descr)
Definition: filtering_audio.c:88
av_get_sample_fmt_name
const char * av_get_sample_fmt_name(enum AVSampleFormat sample_fmt)
Return the name of sample_fmt, or NULL if sample_fmt is not recognized.
Definition: samplefmt.c:51
buffersrc_ctx
AVFilterContext * buffersrc_ctx
Definition: filtering_audio.c:46
AVFormatContext
Format I/O context.
Definition: avformat.h:1104
avfilter_get_by_name
const AVFilter * avfilter_get_by_name(const char *name)
Get a filter definition matching the given name.
Definition: allfilters.c:608
AVStream::codecpar
AVCodecParameters * codecpar
Codec parameters associated with this stream.
Definition: avformat.h:861
avfilter_graph_config
int avfilter_graph_config(AVFilterGraph *graphctx, void *log_ctx)
Check validity and configure all the links and formats in the graph.
Definition: avfiltergraph.c:1167
AVStream::time_base
AVRational time_base
This is the fundamental unit of time (in seconds) in terms of which frame timestamps are represented.
Definition: avformat.h:877
NULL
#define NULL
Definition: coverity.c:32
avcodec_free_context
void avcodec_free_context(AVCodecContext **avctx)
Free the codec context and everything associated with it and write NULL to the provided pointer.
Definition: options.c:168
AVRational
Rational number (pair of numerator and denominator).
Definition: rational.h:58
AVFilterContext::inputs
AVFilterLink ** inputs
array of pointers to input links
Definition: avfilter.h:400
avfilter_inout_alloc
AVFilterInOut * avfilter_inout_alloc(void)
Allocate a single AVFilterInOut entry.
Definition: graphparser.c:201
avcodec_open2
int attribute_align_arg avcodec_open2(AVCodecContext *avctx, const AVCodec *codec, AVDictionary **options)
Initialize the AVCodecContext to use the given AVCodec.
Definition: avcodec.c:115
AVFilterGraph
Definition: avfilter.h:855
inputs
these buffered frames must be flushed immediately if a new input produces new the filter must not call request_frame to get more It must just process the frame or queue it The task of requesting more frames is left to the filter s request_frame method or the application If a filter has several inputs
Definition: filter_design.txt:243
avformat_find_stream_info
int avformat_find_stream_info(AVFormatContext *ic, AVDictionary **options)
Read packets of a media file to get stream information.
Definition: demux.c:2425
av_err2str
#define av_err2str(errnum)
Convenience macro, the return value should be used only directly in function arguments but never stan...
Definition: error.h:121
AVCodecContext::sample_fmt
enum AVSampleFormat sample_fmt
audio sample format
Definition: avcodec.h:1050
AV_OPT_SEARCH_CHILDREN
#define AV_OPT_SEARCH_CHILDREN
Search in possible children of the given object first.
Definition: opt.h:563
filter_descr
static const char * filter_descr
Definition: filtering_audio.c:40
av_packet_alloc
AVPacket * av_packet_alloc(void)
Allocate an AVPacket and set its fields to default values.
Definition: avpacket.c:62
AV_LOG_INFO
#define AV_LOG_INFO
Standard information.
Definition: log.h:191
buffersink.h
av_channel_layout_default
void av_channel_layout_default(AVChannelLayout *ch_layout, int nb_channels)
Get the default channel layout for a given number of channels.
Definition: channel_layout.c:962
avcodec_send_packet
int avcodec_send_packet(AVCodecContext *avctx, const AVPacket *avpkt)
Supply raw packet data as input to a decoder.
Definition: decode.c:598
avfilter_graph_parse_ptr
int avfilter_graph_parse_ptr(AVFilterGraph *graph, const char *filters, AVFilterInOut **inputs, AVFilterInOut **outputs, void *log_ctx)
Add a graph described by a string to a graph.
Definition: graphparser.c:543
avcodec_parameters_to_context
int avcodec_parameters_to_context(AVCodecContext *codec, const AVCodecParameters *par)
Fill the codec context based on the values from the supplied codec parameters.
Definition: codec_par.c:182
av_buffersrc_add_frame_flags
int attribute_align_arg av_buffersrc_add_frame_flags(AVFilterContext *ctx, AVFrame *frame, int flags)
Add a frame to the buffer source.
Definition: buffersrc.c:175
AVSampleFormat
AVSampleFormat
Audio sample formats.
Definition: samplefmt.h:55
print_frame
static void print_frame(const AVFrame *frame)
Definition: filtering_audio.c:201
av_frame_unref
void av_frame_unref(AVFrame *frame)
Unreference all the buffers referenced by frame and reset the frame fields.
Definition: frame.c:474
AV_SAMPLE_FMT_S16
@ AV_SAMPLE_FMT_S16
signed 16 bits
Definition: samplefmt.h:58
fmt_ctx
static AVFormatContext * fmt_ctx
Definition: filtering_audio.c:43
AVFilterPad::name
const char * name
Pad name.
Definition: internal.h:55
avcodec.h
AVFilter
Filter definition.
Definition: avfilter.h:161
ret
ret
Definition: filter_design.txt:187
frame
these buffered frames must be flushed immediately if a new input produces new the filter must not call request_frame to get more It must just process the frame or queue it The task of requesting more frames is left to the filter s request_frame method or the application If a filter has several the filter must be ready for frames arriving randomly on any input any filter with several inputs will most likely require some kind of queuing mechanism It is perfectly acceptable to have a limited queue and to drop frames when the inputs are too unbalanced request_frame For filters that do not use the this method is called when a frame is wanted on an output For a it should directly call filter_frame on the corresponding output For a if there are queued frames already one of these frames should be pushed If the filter should request a frame on one of its repeatedly until at least one frame has been pushed Return or at least make progress towards producing a frame
Definition: filter_design.txt:264
avformat.h
AVCodecContext
main external API structure.
Definition: avcodec.h:426
channel_layout.h
AVRational::den
int den
Denominator.
Definition: rational.h:60
AVPacket::stream_index
int stream_index
Definition: packet.h:376
AVFilterContext
An instance of a filter.
Definition: avfilter.h:392
av_strdup
char * av_strdup(const char *s)
Duplicate a string.
Definition: mem.c:270
AVPacket
This structure stores compressed data.
Definition: packet.h:351
av_log
#define av_log(a,...)
Definition: tableprint_vlc.h:27
AVFilterInOut
A linked-list of the inputs/outputs of the filter chain.
Definition: avfilter.h:1015
snprintf
#define snprintf
Definition: snprintf.h:34
buffersrc.h
audio_stream_index
static int audio_stream_index
Definition: filtering_audio.c:48
av_x_if_null
static void * av_x_if_null(const void *p, const void *x)
Return x default pointer in case p is NULL.
Definition: avutil.h:308
dec_ctx
static AVCodecContext * dec_ctx
Definition: filtering_audio.c:44