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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 doc/examples/filtering_audio.c
29  */
30 
31 #include <unistd.h>
32 
33 #include <libavcodec/avcodec.h>
34 #include <libavformat/avformat.h>
36 #include <libavfilter/avcodec.h>
37 #include <libavfilter/buffersink.h>
38 #include <libavfilter/buffersrc.h>
39 #include <libavutil/opt.h>
40 
41 static const char *filter_descr = "aresample=8000,aformat=sample_fmts=s16:channel_layouts=mono";
42 static const char *player = "ffplay -f s16le -ar 8000 -ac 1 -";
43 
49 static int audio_stream_index = -1;
50 
51 static int open_input_file(const char *filename)
52 {
53  int ret;
54  AVCodec *dec;
55 
56  if ((ret = avformat_open_input(&fmt_ctx, filename, NULL, NULL)) < 0) {
57  av_log(NULL, AV_LOG_ERROR, "Cannot open input file\n");
58  return ret;
59  }
60 
61  if ((ret = avformat_find_stream_info(fmt_ctx, NULL)) < 0) {
62  av_log(NULL, AV_LOG_ERROR, "Cannot find stream information\n");
63  return ret;
64  }
65 
66  /* select the audio stream */
67  ret = av_find_best_stream(fmt_ctx, AVMEDIA_TYPE_AUDIO, -1, -1, &dec, 0);
68  if (ret < 0) {
69  av_log(NULL, AV_LOG_ERROR, "Cannot find a audio stream in the input file\n");
70  return ret;
71  }
73  dec_ctx = fmt_ctx->streams[audio_stream_index]->codec;
74  av_opt_set_int(dec_ctx, "refcounted_frames", 1, 0);
75 
76  /* init the audio decoder */
77  if ((ret = avcodec_open2(dec_ctx, dec, NULL)) < 0) {
78  av_log(NULL, AV_LOG_ERROR, "Cannot open audio decoder\n");
79  return ret;
80  }
81 
82  return 0;
83 }
84 
85 static int init_filters(const char *filters_descr)
86 {
87  char args[512];
88  int ret;
89  AVFilter *abuffersrc = avfilter_get_by_name("abuffer");
90  AVFilter *abuffersink = avfilter_get_by_name("abuffersink");
93  static const enum AVSampleFormat out_sample_fmts[] = { AV_SAMPLE_FMT_S16, -1 };
94  static const int64_t out_channel_layouts[] = { AV_CH_LAYOUT_MONO, -1 };
95  static const int out_sample_rates[] = { 8000, -1 };
96  const AVFilterLink *outlink;
97  AVRational time_base = fmt_ctx->streams[audio_stream_index]->time_base;
98 
99  filter_graph = avfilter_graph_alloc();
100 
101  /* buffer audio source: the decoded frames from the decoder will be inserted here. */
102  if (!dec_ctx->channel_layout)
104  snprintf(args, sizeof(args),
105  "time_base=%d/%d:sample_rate=%d:sample_fmt=%s:channel_layout=0x%"PRIx64,
106  time_base.num, time_base.den, dec_ctx->sample_rate,
107  av_get_sample_fmt_name(dec_ctx->sample_fmt), dec_ctx->channel_layout);
108  ret = avfilter_graph_create_filter(&buffersrc_ctx, abuffersrc, "in",
109  args, NULL, filter_graph);
110  if (ret < 0) {
111  av_log(NULL, AV_LOG_ERROR, "Cannot create audio buffer source\n");
112  return ret;
113  }
114 
115  /* buffer audio sink: to terminate the filter chain. */
116  ret = avfilter_graph_create_filter(&buffersink_ctx, abuffersink, "out",
117  NULL, NULL, filter_graph);
118  if (ret < 0) {
119  av_log(NULL, AV_LOG_ERROR, "Cannot create audio buffer sink\n");
120  return ret;
121  }
122 
123  ret = av_opt_set_int_list(buffersink_ctx, "sample_fmts", out_sample_fmts, -1,
125  if (ret < 0) {
126  av_log(NULL, AV_LOG_ERROR, "Cannot set output sample format\n");
127  return ret;
128  }
129 
130  ret = av_opt_set_int_list(buffersink_ctx, "channel_layouts", out_channel_layouts, -1,
132  if (ret < 0) {
133  av_log(NULL, AV_LOG_ERROR, "Cannot set output channel layout\n");
134  return ret;
135  }
136 
137  ret = av_opt_set_int_list(buffersink_ctx, "sample_rates", out_sample_rates, -1,
139  if (ret < 0) {
140  av_log(NULL, AV_LOG_ERROR, "Cannot set output sample rate\n");
141  return ret;
142  }
143 
144  /* Endpoints for the filter graph. */
145  outputs->name = av_strdup("in");
146  outputs->filter_ctx = buffersrc_ctx;
147  outputs->pad_idx = 0;
148  outputs->next = NULL;
149 
150  inputs->name = av_strdup("out");
151  inputs->filter_ctx = buffersink_ctx;
152  inputs->pad_idx = 0;
153  inputs->next = NULL;
154 
155  if ((ret = avfilter_graph_parse_ptr(filter_graph, filters_descr,
156  &inputs, &outputs, NULL)) < 0)
157  return ret;
158 
159  if ((ret = avfilter_graph_config(filter_graph, NULL)) < 0)
160  return ret;
161 
162  /* Print summary of the sink buffer
163  * Note: args buffer is reused to store channel layout string */
164  outlink = buffersink_ctx->inputs[0];
165  av_get_channel_layout_string(args, sizeof(args), -1, outlink->channel_layout);
166  av_log(NULL, AV_LOG_INFO, "Output: srate:%dHz fmt:%s chlayout:%s\n",
167  (int)outlink->sample_rate,
168  (char *)av_x_if_null(av_get_sample_fmt_name(outlink->format), "?"),
169  args);
170 
171  return 0;
172 }
173 
174 static void print_frame(const AVFrame *frame)
175 {
177  const uint16_t *p = (uint16_t*)frame->data[0];
178  const uint16_t *p_end = p + n;
179 
180  while (p < p_end) {
181  fputc(*p & 0xff, stdout);
182  fputc(*p>>8 & 0xff, stdout);
183  p++;
184  }
185  fflush(stdout);
186 }
187 
188 int main(int argc, char **argv)
189 {
190  int ret;
191  AVPacket packet;
193  AVFrame *filt_frame = av_frame_alloc();
194  int got_frame;
195 
196  if (!frame || !filt_frame) {
197  perror("Could not allocate frame");
198  exit(1);
199  }
200  if (argc != 2) {
201  fprintf(stderr, "Usage: %s file | %s\n", argv[0], player);
202  exit(1);
203  }
204 
206  av_register_all();
208 
209  if ((ret = open_input_file(argv[1])) < 0)
210  goto end;
211  if ((ret = init_filters(filter_descr)) < 0)
212  goto end;
213 
214  /* read all packets */
215  while (1) {
216  if ((ret = av_read_frame(fmt_ctx, &packet)) < 0)
217  break;
218 
219  if (packet.stream_index == audio_stream_index) {
221  got_frame = 0;
222  ret = avcodec_decode_audio4(dec_ctx, frame, &got_frame, &packet);
223  if (ret < 0) {
224  av_log(NULL, AV_LOG_ERROR, "Error decoding audio\n");
225  continue;
226  }
227 
228  if (got_frame) {
229  /* push the audio data from decoded frame into the filtergraph */
230  if (av_buffersrc_add_frame_flags(buffersrc_ctx, frame, 0) < 0) {
231  av_log(NULL, AV_LOG_ERROR, "Error while feeding the audio filtergraph\n");
232  break;
233  }
234 
235  /* pull filtered audio from the filtergraph */
236  while (1) {
237  ret = av_buffersink_get_frame(buffersink_ctx, filt_frame);
238  if(ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
239  break;
240  if(ret < 0)
241  goto end;
242  print_frame(filt_frame);
243  av_frame_unref(filt_frame);
244  }
245  }
246  }
247  av_free_packet(&packet);
248  }
249 end:
250  avfilter_graph_free(&filter_graph);
251  if (dec_ctx)
252  avcodec_close(dec_ctx);
253  avformat_close_input(&fmt_ctx);
254  av_frame_free(&frame);
255  av_frame_free(&filt_frame);
256 
257  if (ret < 0 && ret != AVERROR_EOF) {
258  char buf[1024];
259  av_strerror(ret, buf, sizeof(buf));
260  fprintf(stderr, "Error occurred: %s\n", buf);
261  exit(1);
262  }
263 
264  exit(0);
265 }