hi,
I need to get the decoded samples from audio files of various formats
using libavcodec.
I've modified apiexample.c in order to detect automatically the
appropriate codec, as shown in
http://www.dranger.com/ffmpeg/tutorial03.c
I replaced the following:
<code>
// find the mpeg audio decoder
codec = avcodec_find_decoder(CODEC_ID_MP2);
if (!codec) {
fprintf(stderr, "codec not found\n");
exit(1);
}
c= avcodec_alloc_context();
</code>
by this:
<code>
AVFormatContext *pFormatCtx;
int i, audioStream;
// Open audio file
if(av_open_input_file(&pFormatCtx, filename, NULL, 0, NULL)!=0) {
printf("Couldn't open file\n");
return -1;
}
// Retrieve stream information
if(av_find_stream_info(pFormatCtx)<0)
return -1; // Couldn't find stream information
// Dump information about file onto standard error
dump_format(pFormatCtx, 0, filename, 0);
// Find the first audio stream
audioStream=-1;
for(i=0; i<pFormatCtx->nb_streams; i++) {
if(pFormatCtx->streams[i]->codec->codec_type==CODEC_TYPE_AUDIO
&& audioStream < 0) {
audioStream=i;
}
}
if(audioStream==-1)
return -1;
c=pFormatCtx->streams[audioStream]->codec;
</code>
in apiexample.c (I also included avformat.h of course).
My problem is that it does not even open the file, i.e.
<code>
av_open_input_file(&pFormatCtx, filename, NULL, 0, NULL) do not return 0
</code>
do not return 0.
The original code (i.e. hardcoding codec =
avcodec_find_decoder(CODEC_ID_MP2);) works...
Is this the right way to do what I want to achieve?
apiexample_modified.c is attached.
thank you
Jul
/*
* copyright (c) 2001 Fabrice Bellard
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file apiexample.c
* avcodec API use example.
*
* Note that this library only handles codecs (mpeg, mpeg4, etc...),
* not file formats (avi, vob, etc...). See library 'libavformat' for the
* format handling
*/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#define PI 3.14159265358979323846
#ifdef HAVE_AV_CONFIG_H
#undef HAVE_AV_CONFIG_H
#endif
#include "ffmpeg/avcodec.h"
#include "ffmpeg/avformat.h"
#define INBUF_SIZE 4096
/*
* Audio encoding example
*/
void audio_encode_example(const char *filename)
{
AVCodec *codec;
AVCodecContext *c= NULL;
int frame_size, i, j, out_size, outbuf_size;
FILE *f;
short *samples;
float t, tincr;
uint8_t *outbuf;
printf("Audio encoding\n");
/* find the MP2 encoder */
codec = avcodec_find_encoder(CODEC_ID_MP2);
if (!codec) {
fprintf(stderr, "codec not found\n");
exit(1);
}
c= avcodec_alloc_context();
/* put sample parameters */
c->bit_rate = 64000;
c->sample_rate = 44100;
c->channels = 2;
/* open it */
if (avcodec_open(c, codec) < 0) {
fprintf(stderr, "could not open codec\n");
exit(1);
}
/* the codec gives us the frame size, in samples */
frame_size = c->frame_size;
samples = malloc(frame_size * 2 * c->channels);
outbuf_size = 10000;
outbuf = malloc(outbuf_size);
f = fopen(filename, "wb");
if (!f) {
fprintf(stderr, "could not open %s\n", filename);
exit(1);
}
/* encode a single tone sound */
t = 0;
tincr = 2 * PI * 440.0 / c->sample_rate;
for(i=0;i<200;i++) {
for(j=0;j<frame_size;j++) {
samples[2*j] = (int)(sin(t) * 10000);
samples[2*j+1] = samples[2*j];
t += tincr;
}
/* encode the samples */
out_size = avcodec_encode_audio(c, outbuf, outbuf_size, samples);
fwrite(outbuf, 1, out_size, f);
}
fclose(f);
free(outbuf);
free(samples);
avcodec_close(c);
av_free(c);
}
/*
* Audio decoding.
*/
int audio_decode_example(const char *outfilename, const char *filename)
{
AVCodec *codec;
AVCodecContext *c= NULL;
int out_size, size, len;
FILE *f, *outfile;
uint8_t *outbuf;
uint8_t inbuf[INBUF_SIZE + FF_INPUT_BUFFER_PADDING_SIZE], *inbuf_ptr;
printf("Audio decoding\n");
////////// original code /////////////////////////////////////////////
/*
// find the mpeg audio decoder
codec = avcodec_find_decoder(CODEC_ID_MP2);
if (!codec) {
fprintf(stderr, "codec not found\n");
exit(1);
}
c= avcodec_alloc_context();
*/
////////// code from http://www.dranger.com/ffmpeg/tutorial03.c /////////////
AVFormatContext *pFormatCtx;
int i, audioStream;
// Open audio file
if(av_open_input_file(&pFormatCtx, filename, NULL, 0, NULL)!=0) {
printf("Couldn't open file\n");
return -1;
}
// Retrieve stream information
if(av_find_stream_info(pFormatCtx)<0)
return -1; // Couldn't find stream information
// Dump information about file onto standard error
dump_format(pFormatCtx, 0, filename, 0);
// Find the first audio stream
audioStream=-1;
for(i=0; i<pFormatCtx->nb_streams; i++) {
if(pFormatCtx->streams[i]->codec->codec_type==CODEC_TYPE_AUDIO && audioStream < 0) {
audioStream=i;
}
}
if(audioStream==-1)
return -1;
c=pFormatCtx->streams[audioStream]->codec;
////////////////////////////////////
/* open it */
if (avcodec_open(c, codec) < 0) {
fprintf(stderr, "could not open codec\n");
exit(1);
}
outbuf = malloc(AVCODEC_MAX_AUDIO_FRAME_SIZE);
f = fopen(filename, "rb");
if (!f) {
fprintf(stderr, "could not open %s\n", filename);
exit(1);
}
outfile = fopen(outfilename, "wb");
if (!outfile) {
av_free(c);
exit(1);
}
/* decode until eof */
inbuf_ptr = inbuf;
for(;;) {
size = fread(inbuf, 1, INBUF_SIZE, f);
if (size == 0)
break;
inbuf_ptr = inbuf;
while (size > 0) {
len = avcodec_decode_audio(c, (short *)outbuf, &out_size,
inbuf_ptr, size);
if (len < 0) {
fprintf(stderr, "Error while decoding\n");
exit(1);
}
if (out_size > 0) {
/* if a frame has been decoded, output it */
fwrite(outbuf, 1, out_size, outfile);
}
size -= len;
inbuf_ptr += len;
}
}
fclose(outfile);
fclose(f);
free(outbuf);
avcodec_close(c);
av_free(c);
}
int main(int argc, char **argv)
{
const char *filename;
/* must be called before using avcodec lib */
avcodec_init();
/* register all the codecs */
avcodec_register_all();
if (argc <= 1) {
audio_encode_example("/tmp/test.mp2");
audio_decode_example("/tmp/test.sw", "/tmp/test.mp2");
} else {
filename = argv[1];
}
return 0;
}
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