FFmpeg 5.1.6
filtering_audio.c
Go to the documentation of this file.
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>
38#include <libavutil/opt.h>
39
40static const char *filter_descr = "aresample=8000,aformat=sample_fmts=s16:channel_layouts=mono";
41static const char *player = "ffplay -f s16le -ar 8000 -ac 1 -";
42
48static int audio_stream_index = -1;
49
50static 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 */
66 ret = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_AUDIO, -1, -1, &dec, 0);
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
88static 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",
124 NULL, NULL, filter_graph);
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
182 if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0)
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
194end:
195 avfilter_inout_free(&inputs);
196 avfilter_inout_free(&outputs);
197
198 return ret;
199}
200
201static 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
215int 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) {
266 ret = av_buffersink_get_frame(buffersink_ctx, filt_frame);
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 }
280end:
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}
Libavcodec external API header.
Main libavformat public API header.
memory buffer sink API for audio and video
Memory buffer source API.
audio channel layout utility functions
static AVFrame * frame
AVFilterGraph * filter_graph
int main(int argc, char **argv)
static AVFormatContext * fmt_ctx
AVFilterContext * buffersink_ctx
static const char * filter_descr
static int audio_stream_index
AVFilterContext * buffersrc_ctx
static const char * player
static int open_input_file(const char *filename)
static int init_filters(const char *filters_descr)
static AVCodecContext * dec_ctx
static void print_frame(const AVFrame *frame)
#define AV_OPT_SEARCH_CHILDREN
Search in possible children of the given object first.
Definition: opt.h:563
int avcodec_open2(AVCodecContext *avctx, const AVCodec *codec, AVDictionary **options)
Initialize the AVCodecContext to use the given AVCodec.
AVCodecContext * avcodec_alloc_context3(const AVCodec *codec)
Allocate an AVCodecContext and set its fields to default values.
int avcodec_parameters_to_context(AVCodecContext *codec, const AVCodecParameters *par)
Fill the codec context based on the values from the supplied codec parameters.
void avcodec_free_context(AVCodecContext **avctx)
Free the codec context and everything associated with it and write NULL to the provided pointer.
int avcodec_receive_frame(AVCodecContext *avctx, AVFrame *frame)
Return decoded output data from a decoder.
int avcodec_send_packet(AVCodecContext *avctx, const AVPacket *avpkt)
Supply raw packet data as input to a decoder.
void av_packet_free(AVPacket **pkt)
Free the packet, if the packet is reference counted, it will be unreferenced first.
void av_packet_unref(AVPacket *pkt)
Wipe the packet.
AVPacket * av_packet_alloc(void)
Allocate an AVPacket and set its fields to default values.
int av_read_frame(AVFormatContext *s, AVPacket *pkt)
Return the next frame of a 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.
int avformat_open_input(AVFormatContext **ps, const char *url, const AVInputFormat *fmt, AVDictionary **options)
Open an input stream and read the header.
int avformat_find_stream_info(AVFormatContext *ic, AVDictionary **options)
Read packets of a media file to get stream information.
void avformat_close_input(AVFormatContext **s)
Close an opened input AVFormatContext.
int av_buffersink_get_frame(AVFilterContext *ctx, AVFrame *frame)
Get a frame with filtered data from sink and put it in frame.
av_warn_unused_result int av_buffersrc_add_frame_flags(AVFilterContext *buffer_src, AVFrame *frame, int flags)
Add a frame to the buffer source.
@ AV_BUFFERSRC_FLAG_KEEP_REF
Keep a reference to the frame.
Definition: buffersrc.h:53
int avfilter_graph_config(AVFilterGraph *graphctx, void *log_ctx)
Check validity and configure all the links and formats in the graph.
const AVFilter * avfilter_get_by_name(const char *name)
Get a filter definition matching the given name.
void avfilter_inout_free(AVFilterInOut **inout)
Free the supplied list of AVFilterInOut and set *inout to NULL.
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.
void avfilter_graph_free(AVFilterGraph **graph)
Free a graph, destroy its links, and set *graph to NULL.
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.
AVFilterInOut * avfilter_inout_alloc(void)
Allocate a single AVFilterInOut entry.
AVFilterGraph * avfilter_graph_alloc(void)
Allocate a filter graph.
void av_channel_layout_default(AVChannelLayout *ch_layout, int nb_channels)
Get the default channel layout for a given number of channels.
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.
@ AV_CHANNEL_ORDER_UNSPEC
Only the channel count is specified, without any further information about the channel order.
#define AVERROR_EOF
End of file.
Definition: error.h:57
#define av_err2str(errnum)
Convenience macro, the return value should be used only directly in function arguments but never stan...
Definition: error.h:121
#define AVERROR(e)
Definition: error.h:45
void av_frame_unref(AVFrame *frame)
Unreference all the buffers referenced by frame and reset the frame fields.
void av_frame_free(AVFrame **frame)
Free the frame and any dynamically allocated objects in it, e.g.
AVFrame * av_frame_alloc(void)
Allocate an AVFrame and set its fields to default values.
#define AV_LOG_INFO
Standard information.
Definition: log.h:191
#define AV_LOG_ERROR
Something went wrong and cannot losslessly be recovered.
Definition: log.h:180
void av_log(void *avcl, int level, const char *fmt,...) av_printf_format(3
Send the specified message to the log if the level is less than or equal to the current av_log_level.
char * av_strdup(const char *s) av_malloc_attrib
Duplicate a string.
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
@ AVMEDIA_TYPE_AUDIO
Definition: avutil.h:202
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.
AVSampleFormat
Audio sample formats.
Definition: samplefmt.h:55
@ AV_SAMPLE_FMT_S16
signed 16 bits
Definition: samplefmt.h:58
int av_opt_set(void *obj, const char *name, const char *val, int search_flags)
#define av_opt_set_int_list(obj, name, val, term, flags)
Set a binary option to an integer list.
Definition: opt.h:721
AVOptions.
enum AVChannelOrder order
Channel order used in this layout.
int nb_channels
Number of channels in this layout.
main external API structure.
Definition: avcodec.h:389
AVChannelLayout ch_layout
Audio channel layout.
Definition: avcodec.h:2056
enum AVSampleFormat sample_fmt
audio sample format
Definition: avcodec.h:1014
int sample_rate
samples per second
Definition: avcodec.h:998
AVCodec.
Definition: codec.h:196
An instance of a filter.
Definition: avfilter.h:408
AVFilterLink ** inputs
array of pointers to input links
Definition: avfilter.h:416
A linked-list of the inputs/outputs of the filter chain.
Definition: avfilter.h:1031
AVFilterContext * filter_ctx
filter context associated to this input/output
Definition: avfilter.h:1036
int pad_idx
index of the filt_ctx pad to use for linking
Definition: avfilter.h:1039
char * name
unique name for this input/output in the list
Definition: avfilter.h:1033
struct AVFilterInOut * next
next input/input in the list, NULL if this is the last
Definition: avfilter.h:1042
Filter definition.
Definition: avfilter.h:171
Format I/O context.
Definition: avformat.h:1213
AVStream ** streams
A list of all streams in the file.
Definition: avformat.h:1281
This structure describes decoded (raw) audio or video data.
Definition: frame.h:325
int nb_samples
number of audio samples (per channel) described by this frame
Definition: frame.h:405
uint8_t * data[AV_NUM_DATA_POINTERS]
pointer to the picture/channel planes.
Definition: frame.h:346
AVChannelLayout ch_layout
Channel layout of the audio data.
Definition: frame.h:704
This structure stores compressed data.
Definition: packet.h:351
int stream_index
Definition: packet.h:376
Rational number (pair of numerator and denominator).
Definition: rational.h:58
int num
Numerator.
Definition: rational.h:59
int den
Denominator.
Definition: rational.h:60
AVCodecParameters * codecpar
Codec parameters associated with this stream.
Definition: avformat.h:1108
AVRational time_base
This is the fundamental unit of time (in seconds) in terms of which frame timestamps are represented.
Definition: avformat.h:978