doc/examples/decode_audio.c

   1 /*
   2  * copyright (c) 2001 Fabrice Bellard
   3  *
   4  * This file is part of Libav.
   5  *
   6  * Libav is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU Lesser General Public
   8  * License as published by the Free Software Foundation; either
   9  * version 2.1 of the License, or (at your option) any later version.
  10  *
  11  * Libav is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14  * Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public
  17  * License along with Libav; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  19  */
  20
  21 /**
  22  * @file
  23  * audio decoding with libavcodec API example
  24  *
  25  * @example decode_audio.c
  26  */
  27
  28 #include <stdio.h>
  29 #include <stdlib.h>
  30 #include <string.h>
  31
  32 #include "libavutil/channel_layout.h"
  33 #include "libavutil/frame.h"
  34 #include "libavutil/mem.h"
  35
  36 #include "libavcodec/avcodec.h"
  37
  38 #define AUDIO_INBUF_SIZE 20480
  39 #define AUDIO_REFILL_THRESH 4096
  40
  41 static void decode(AVCodecContext *dec_ctx, AVPacket *pkt, AVFrame *frame,
  42                    FILE *outfile)
  43 {
  44     int16_t *interleave_buf;
  45     int ret, data_size, i;
  46
  47     /* send the packet with the compressed data to the decoder */
  48     ret = avcodec_send_packet(dec_ctx, pkt);
  49     if (ret < 0) {
  50         fprintf(stderr, "Error submitting the packet to the decoder\n");
  51         exit(1);
  52     }
  53
  54     /* read all the output frames (in general there may be any number of them */
  55     while (ret >= 0) {
  56         ret = avcodec_receive_frame(dec_ctx, frame);
  57         if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)
  58             return;
  59         else if (ret < 0) {
  60             fprintf(stderr, "Error during decoding\n");
  61             exit(1);
  62         }
  63
  64         /* the stream parameters may change at any time, check that they are
  65          * what we expect */
  66         if (av_get_channel_layout_nb_channels(frame->channel_layout) != 2 ||
  67             frame->format != AV_SAMPLE_FMT_S16P) {
  68             fprintf(stderr, "Unsupported frame parameters\n");
  69             exit(1);
  70         }
  71
  72         /* The decoded data is signed 16-bit planar -- each channel in its own
  73          * buffer. We interleave the two channels manually here, but using
  74          * libavresample is recommended instead. */
  75         data_size = sizeof(*interleave_buf) * 2 * frame->nb_samples;
  76         interleave_buf = av_malloc(data_size);
  77         if (!interleave_buf)
  78             exit(1);
  79
  80         for (i = 0; i < frame->nb_samples; i++) {
  81             interleave_buf[2 * i]     = ((int16_t*)frame->data[0])[i];
  82             interleave_buf[2 * i + 1] = ((int16_t*)frame->data[1])[i];
  83         }
  84         fwrite(interleave_buf, 1, data_size, outfile);
  85         av_freep(&interleave_buf);
  86     }
  87 }
  88
  89 int main(int argc, char **argv)
  90 {
  91     const char *outfilename, *filename;
  92     const AVCodec *codec;
  93     AVCodecContext *c= NULL;
  94     AVCodecParserContext *parser = NULL;
  95     int len, ret;
  96     FILE *f, *outfile;
  97     uint8_t inbuf[AUDIO_INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];
  98     uint8_t *data;
  99     size_t   data_size;
 100     AVPacket avpkt;
 101     AVFrame *decoded_frame = NULL;
 102
 103     if (argc <= 2) {
 104         fprintf(stderr, "Usage: %s <input file> <output file>\n", argv[0]);
 105         exit(0);
 106     }
 107     filename    = argv[1];
 108     outfilename = argv[2];
 109
 110     /* register all the codecs */
 111     avcodec_register_all();
 112
 113     av_init_packet(&avpkt);
 114
 115     /* find the MPEG audio decoder */
 116     codec = avcodec_find_decoder(AV_CODEC_ID_MP2);
 117     if (!codec) {
 118         fprintf(stderr, "codec not found\n");
 119         exit(1);
 120     }
 121
 122     parser = av_parser_init(codec->id);
 123     if (!parser) {
 124         fprintf(stderr, "parser not found\n");
 125         exit(1);
 126     }
 127
 128     c = avcodec_alloc_context3(codec);
 129
 130     /* open it */
 131     if (avcodec_open2(c, codec, NULL) < 0) {
 132         fprintf(stderr, "could not open codec\n");
 133         exit(1);
 134     }
 135
 136     f = fopen(filename, "rb");
 137     if (!f) {
 138         fprintf(stderr, "could not open %s\n", filename);
 139         exit(1);
 140     }
 141     outfile = fopen(outfilename, "wb");
 142     if (!outfile) {
 143         av_free(c);
 144         exit(1);
 145     }
 146
 147     /* decode until eof */
 148     data      = inbuf;
 149     data_size = fread(inbuf, 1, AUDIO_INBUF_SIZE, f);
 150
 151     while (data_size > 0) {
 152         if (!decoded_frame) {
 153             if (!(decoded_frame = av_frame_alloc())) {
 154                 fprintf(stderr, "out of memory\n");
 155                 exit(1);
 156             }
 157         }
 158
 159         ret = av_parser_parse2(parser, c, &avpkt.data, &avpkt.size,
 160                                data, data_size,
 161                                AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);
 162         if (ret < 0) {
 163             fprintf(stderr, "Error while parsing\n");
 164             exit(1);
 165         }
 166         data      += ret;
 167         data_size -= ret;
 168
 169         if (avpkt.size)
 170             decode(c, &avpkt, decoded_frame, outfile);
 171
 172         if (data_size < AUDIO_REFILL_THRESH) {
 173             memmove(inbuf, data, data_size);
 174             data = inbuf;
 175             len = fread(data + data_size, 1,
 176                         AUDIO_INBUF_SIZE - data_size, f);
 177             if (len > 0)
 178                 data_size += len;
 179         }
 180     }
 181
 182     fclose(outfile);
 183     fclose(f);
 184
 185     avcodec_free_context(&c);
 186     av_parser_close(parser);
 187     av_frame_free(&decoded_frame);
 188
 189     return 0;
 190 }