FFmpeg  5.1.1
encode_audio.c
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1 /*
2  * Copyright (c) 2001 Fabrice Bellard
3  *
4  * Permission is hereby granted, free of charge, to any person obtaining a copy
5  * of this software and associated documentation files (the "Software"), to deal
6  * in the Software without restriction, including without limitation the rights
7  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
8  * copies of the Software, and to permit persons to whom the Software is
9  * furnished to do so, subject to the following conditions:
10  *
11  * The above copyright notice and this permission notice shall be included in
12  * all copies or substantial portions of the Software.
13  *
14  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
15  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
16  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
17  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
18  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
19  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
20  * THE SOFTWARE.
21  */
22 
23 /**
24  * @file
25  * audio encoding with libavcodec API example.
26  *
27  * @example encode_audio.c
28  */
29 
30 #include <stdint.h>
31 #include <stdio.h>
32 #include <stdlib.h>
33 
34 #include <libavcodec/avcodec.h>
35 
37 #include <libavutil/common.h>
38 #include <libavutil/frame.h>
39 #include <libavutil/samplefmt.h>
40 
41 /* check that a given sample format is supported by the encoder */
42 static int check_sample_fmt(const AVCodec *codec, enum AVSampleFormat sample_fmt)
43 {
44  const enum AVSampleFormat *p = codec->sample_fmts;
45 
46  while (*p != AV_SAMPLE_FMT_NONE) {
47  if (*p == sample_fmt)
48  return 1;
49  p++;
50  }
51  return 0;
52 }
53 
54 /* just pick the highest supported samplerate */
55 static int select_sample_rate(const AVCodec *codec)
56 {
57  const int *p;
58  int best_samplerate = 0;
59 
60  if (!codec->supported_samplerates)
61  return 44100;
62 
63  p = codec->supported_samplerates;
64  while (*p) {
65  if (!best_samplerate || abs(44100 - *p) < abs(44100 - best_samplerate))
66  best_samplerate = *p;
67  p++;
68  }
69  return best_samplerate;
70 }
71 
72 /* select layout with the highest channel count */
73 static int select_channel_layout(const AVCodec *codec, AVChannelLayout *dst)
74 {
75  const AVChannelLayout *p, *best_ch_layout;
76  int best_nb_channels = 0;
77 
78  if (!codec->ch_layouts)
80 
81  p = codec->ch_layouts;
82  while (p->nb_channels) {
83  int nb_channels = p->nb_channels;
84 
85  if (nb_channels > best_nb_channels) {
86  best_ch_layout = p;
87  best_nb_channels = nb_channels;
88  }
89  p++;
90  }
91  return av_channel_layout_copy(dst, best_ch_layout);
92 }
93 
95  FILE *output)
96 {
97  int ret;
98 
99  /* send the frame for encoding */
100  ret = avcodec_send_frame(ctx, frame);
101  if (ret < 0) {
102  fprintf(stderr, "Error sending the frame to the encoder\n");
103  exit(1);
104  }
105 
106  /* read all the available output packets (in general there may be any
107  * number of them */
108  while (ret >= 0) {
109  ret = avcodec_receive_packet(ctx, pkt);
110  if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
111  return;
112  else if (ret < 0) {
113  fprintf(stderr, "Error encoding audio frame\n");
114  exit(1);
115  }
116 
117  fwrite(pkt->data, 1, pkt->size, output);
119  }
120 }
121 
122 int main(int argc, char **argv)
123 {
124  const char *filename;
125  const AVCodec *codec;
126  AVCodecContext *c= NULL;
127  AVFrame *frame;
128  AVPacket *pkt;
129  int i, j, k, ret;
130  FILE *f;
131  uint16_t *samples;
132  float t, tincr;
133 
134  if (argc <= 1) {
135  fprintf(stderr, "Usage: %s <output file>\n", argv[0]);
136  return 0;
137  }
138  filename = argv[1];
139 
140  /* find the MP2 encoder */
142  if (!codec) {
143  fprintf(stderr, "Codec not found\n");
144  exit(1);
145  }
146 
147  c = avcodec_alloc_context3(codec);
148  if (!c) {
149  fprintf(stderr, "Could not allocate audio codec context\n");
150  exit(1);
151  }
152 
153  /* put sample parameters */
154  c->bit_rate = 64000;
155 
156  /* check that the encoder supports s16 pcm input */
158  if (!check_sample_fmt(codec, c->sample_fmt)) {
159  fprintf(stderr, "Encoder does not support sample format %s",
161  exit(1);
162  }
163 
164  /* select other audio parameters supported by the encoder */
165  c->sample_rate = select_sample_rate(codec);
166  ret = select_channel_layout(codec, &c->ch_layout);
167  if (ret < 0)
168  exit(1);
169 
170  /* open it */
171  if (avcodec_open2(c, codec, NULL) < 0) {
172  fprintf(stderr, "Could not open codec\n");
173  exit(1);
174  }
175 
176  f = fopen(filename, "wb");
177  if (!f) {
178  fprintf(stderr, "Could not open %s\n", filename);
179  exit(1);
180  }
181 
182  /* packet for holding encoded output */
183  pkt = av_packet_alloc();
184  if (!pkt) {
185  fprintf(stderr, "could not allocate the packet\n");
186  exit(1);
187  }
188 
189  /* frame containing input raw audio */
190  frame = av_frame_alloc();
191  if (!frame) {
192  fprintf(stderr, "Could not allocate audio frame\n");
193  exit(1);
194  }
195 
197  frame->format = c->sample_fmt;
199  if (ret < 0)
200  exit(1);
201 
202  /* allocate the data buffers */
203  ret = av_frame_get_buffer(frame, 0);
204  if (ret < 0) {
205  fprintf(stderr, "Could not allocate audio data buffers\n");
206  exit(1);
207  }
208 
209  /* encode a single tone sound */
210  t = 0;
211  tincr = 2 * M_PI * 440.0 / c->sample_rate;
212  for (i = 0; i < 200; i++) {
213  /* make sure the frame is writable -- makes a copy if the encoder
214  * kept a reference internally */
216  if (ret < 0)
217  exit(1);
218  samples = (uint16_t*)frame->data[0];
219 
220  for (j = 0; j < c->frame_size; j++) {
221  samples[2*j] = (int)(sin(t) * 10000);
222 
223  for (k = 1; k < c->ch_layout.nb_channels; k++)
224  samples[2*j + k] = samples[2*j];
225  t += tincr;
226  }
227  encode(c, frame, pkt, f);
228  }
229 
230  /* flush the encoder */
231  encode(c, NULL, pkt, f);
232 
233  fclose(f);
234 
238 
239  return 0;
240 }
Libavcodec external API header.
audio channel layout utility functions
common internal and external API header
static AVPacket * pkt
static AVFrame * frame
static int select_channel_layout(const AVCodec *codec, AVChannelLayout *dst)
Definition: encode_audio.c:73
int main(int argc, char **argv)
Definition: encode_audio.c:122
static void encode(AVCodecContext *ctx, AVFrame *frame, AVPacket *pkt, FILE *output)
Definition: encode_audio.c:94
static int check_sample_fmt(const AVCodec *codec, enum AVSampleFormat sample_fmt)
Definition: encode_audio.c:42
static int select_sample_rate(const AVCodec *codec)
Definition: encode_audio.c:55
reference-counted frame API
int avcodec_open2(AVCodecContext *avctx, const AVCodec *codec, AVDictionary **options)
Initialize the AVCodecContext to use the given AVCodec.
const AVCodec * avcodec_find_encoder(enum AVCodecID id)
Find a registered encoder with a matching codec ID.
AVCodecContext * avcodec_alloc_context3(const AVCodec *codec)
Allocate an AVCodecContext and set its fields to default values.
void avcodec_free_context(AVCodecContext **avctx)
Free the codec context and everything associated with it and write NULL to the provided pointer.
@ AV_CODEC_ID_MP2
Definition: codec_id.h:427
int avcodec_receive_packet(AVCodecContext *avctx, AVPacket *avpkt)
Read encoded data from the encoder.
int avcodec_send_frame(AVCodecContext *avctx, const AVFrame *frame)
Supply a raw video or audio frame to the encoder.
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.
#define AV_CHANNEL_LAYOUT_STEREO
int av_channel_layout_copy(AVChannelLayout *dst, const AVChannelLayout *src)
Make a copy of a channel layout.
#define AVERROR_EOF
End of file.
Definition: error.h:57
#define AVERROR(e)
Definition: error.h:45
int av_frame_get_buffer(AVFrame *frame, int align)
Allocate new buffer(s) for audio or video data.
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.
int av_frame_make_writable(AVFrame *frame)
Ensure that the frame data is writable, avoiding data copy if possible.
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_NONE
Definition: samplefmt.h:56
@ AV_SAMPLE_FMT_S16
signed 16 bits
Definition: samplefmt.h:58
#define M_PI
Definition: mathematics.h:52
An AVChannelLayout holds information about the channel layout of audio data.
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
int64_t bit_rate
the average bitrate
Definition: avcodec.h:439
int sample_rate
samples per second
Definition: avcodec.h:998
int frame_size
Number of samples per channel in an audio frame.
Definition: avcodec.h:1026
AVCodec.
Definition: codec.h:196
const AVChannelLayout * ch_layouts
Array of supported channel layouts, terminated with a zeroed layout.
Definition: codec.h:246
enum AVSampleFormat * sample_fmts
array of supported sample formats, or NULL if unknown, array is terminated by -1
Definition: codec.h:220
const int * supported_samplerates
array of supported audio samplerates, or NULL if unknown, array is terminated by 0
Definition: codec.h:219
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
int format
format of the frame, -1 if unknown or unset Values correspond to enum AVPixelFormat for video frames,...
Definition: frame.h:412
This structure stores compressed data.
Definition: packet.h:351
int size
Definition: packet.h:375
uint8_t * data
Definition: packet.h:374