FFmpeg 4.2.2
encode_audio.c
Go to the documentation of this file.
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 */
42static 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 */
55static 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 */
73static int select_channel_layout(const AVCodec *codec)
74{
75 const uint64_t *p;
76 uint64_t best_ch_layout = 0;
77 int best_nb_channels = 0;
78
79 if (!codec->channel_layouts)
81
82 p = codec->channel_layouts;
83 while (*p) {
84 int nb_channels = av_get_channel_layout_nb_channels(*p);
85
86 if (nb_channels > best_nb_channels) {
87 best_ch_layout = *p;
88 best_nb_channels = nb_channels;
89 }
90 p++;
91 }
92 return best_ch_layout;
93}
94
96 FILE *output)
97{
98 int ret;
99
100 /* send the frame for encoding */
101 ret = avcodec_send_frame(ctx, frame);
102 if (ret < 0) {
103 fprintf(stderr, "Error sending the frame to the encoder\n");
104 exit(1);
105 }
106
107 /* read all the available output packets (in general there may be any
108 * number of them */
109 while (ret >= 0) {
110 ret = avcodec_receive_packet(ctx, pkt);
111 if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
112 return;
113 else if (ret < 0) {
114 fprintf(stderr, "Error encoding audio frame\n");
115 exit(1);
116 }
117
118 fwrite(pkt->data, 1, pkt->size, output);
120 }
121}
122
123int main(int argc, char **argv)
124{
125 const char *filename;
126 const AVCodec *codec;
127 AVCodecContext *c= NULL;
128 AVFrame *frame;
129 AVPacket *pkt;
130 int i, j, k, ret;
131 FILE *f;
132 uint16_t *samples;
133 float t, tincr;
134
135 if (argc <= 1) {
136 fprintf(stderr, "Usage: %s <output file>\n", argv[0]);
137 return 0;
138 }
139 filename = argv[1];
140
141 /* find the MP2 encoder */
143 if (!codec) {
144 fprintf(stderr, "Codec not found\n");
145 exit(1);
146 }
147
148 c = avcodec_alloc_context3(codec);
149 if (!c) {
150 fprintf(stderr, "Could not allocate audio codec context\n");
151 exit(1);
152 }
153
154 /* put sample parameters */
155 c->bit_rate = 64000;
156
157 /* check that the encoder supports s16 pcm input */
159 if (!check_sample_fmt(codec, c->sample_fmt)) {
160 fprintf(stderr, "Encoder does not support sample format %s",
162 exit(1);
163 }
164
165 /* select other audio parameters supported by the encoder */
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 */
184 if (!pkt) {
185 fprintf(stderr, "could not allocate the packet\n");
186 exit(1);
187 }
188
189 /* frame containing input raw audio */
191 if (!frame) {
192 fprintf(stderr, "Could not allocate audio frame\n");
193 exit(1);
194 }
195
197 frame->format = c->sample_fmt;
199
200 /* allocate the data buffers */
201 ret = av_frame_get_buffer(frame, 0);
202 if (ret < 0) {
203 fprintf(stderr, "Could not allocate audio data buffers\n");
204 exit(1);
205 }
206
207 /* encode a single tone sound */
208 t = 0;
209 tincr = 2 * M_PI * 440.0 / c->sample_rate;
210 for (i = 0; i < 200; i++) {
211 /* make sure the frame is writable -- makes a copy if the encoder
212 * kept a reference internally */
214 if (ret < 0)
215 exit(1);
216 samples = (uint16_t*)frame->data[0];
217
218 for (j = 0; j < c->frame_size; j++) {
219 samples[2*j] = (int)(sin(t) * 10000);
220
221 for (k = 1; k < c->channels; k++)
222 samples[2*j + k] = samples[2*j];
223 t += tincr;
224 }
225 encode(c, frame, pkt, f);
226 }
227
228 /* flush the encoder */
229 encode(c, NULL, pkt, f);
230
231 fclose(f);
232
236
237 return 0;
238}
Libavcodec external API header.
audio channel layout utility functions
common internal and external API header
static AVPacket pkt
static AVFrame * frame
int main(int argc, char **argv)
Definition: encode_audio.c:123
static void encode(AVCodecContext *ctx, AVFrame *frame, AVPacket *pkt, FILE *output)
Definition: encode_audio.c:95
static int select_channel_layout(const AVCodec *codec)
Definition: encode_audio.c:73
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
#define AV_CH_LAYOUT_STEREO
int av_get_channel_layout_nb_channels(uint64_t channel_layout)
Return the number of channels in the channel layout.
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.
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: avcodec.h:564
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.
AVCodec * avcodec_find_encoder(enum AVCodecID id)
Find a registered encoder with a matching codec ID.
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 AVERROR_EOF
End of file.
Definition: error.h:55
#define AVERROR(e)
Definition: error.h:43
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:58
@ AV_SAMPLE_FMT_NONE
Definition: samplefmt.h:59
@ AV_SAMPLE_FMT_S16
signed 16 bits
Definition: samplefmt.h:61
#define M_PI
Definition: mathematics.h:52
main external API structure.
Definition: avcodec.h:1565
enum AVSampleFormat sample_fmt
audio sample format
Definition: avcodec.h:2233
int64_t bit_rate
the average bitrate
Definition: avcodec.h:1615
int sample_rate
samples per second
Definition: avcodec.h:2225
int channels
number of audio channels
Definition: avcodec.h:2226
uint64_t channel_layout
Audio channel layout.
Definition: avcodec.h:2276
int frame_size
Number of samples per channel in an audio frame.
Definition: avcodec.h:2245
AVCodec.
Definition: avcodec.h:3481
const uint64_t * channel_layouts
array of support channel layouts, or NULL if unknown. array is terminated by 0
Definition: avcodec.h:3505
enum AVSampleFormat * sample_fmts
array of supported sample formats, or NULL if unknown, array is terminated by -1
Definition: avcodec.h:3504
const int * supported_samplerates
array of supported audio samplerates, or NULL if unknown, array is terminated by 0
Definition: avcodec.h:3503
This structure describes decoded (raw) audio or video data.
Definition: frame.h:295
int nb_samples
number of audio samples (per channel) described by this frame
Definition: frame.h:361
uint8_t * data[AV_NUM_DATA_POINTERS]
pointer to the picture/channel planes.
Definition: frame.h:309
uint64_t channel_layout
Channel layout of the audio data.
Definition: frame.h:472
int format
format of the frame, -1 if unknown or unset Values correspond to enum AVPixelFormat for video frames,...
Definition: frame.h:368
This structure stores compressed data.
Definition: avcodec.h:1454
int size
Definition: avcodec.h:1478
uint8_t * data
Definition: avcodec.h:1477