Decoding with FFMPEG on Visual Studio 2010 - c++

Question

I just started using FFMPEG with C++ and try to code an audio decoder then write the decoded audio into a file.
However i'm not sure about which data to write to the output file. As far as i know from looking at the sample codes it seems to be the AVFrame -> data[0].
But when i try to print it on the consoles, i get some random numbers that are different each time i run the program. And when i try to write this AVFrame->data[0] into a file i keep getting an error.
So my question is how can I write the decoded audio after I call the function av_codec_decode_audio4 ?
Below I attached my code and I pass the argument "C:\02.mp3" which is a path for a valid mp3 file on my PC.
Thank you for your help.
// TestFFMPEG.cpp : Audio Decoder
//
#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <sstream>
extern "C" {
#include <avcodec.h>
#include <avformat.h>
#include <swscale.h>
}
using namespace std;
int main(int argc, char* argv[])
{
int audioStream = -1;
AVCodec *aCodec;
AVPacket avPkt;
AVFrame *decode_frame = avcodec_alloc_frame();
AVCodecContext *aCodecCtxt;
AVFormatContext *pFormatCtxt = NULL;
if(argc != 2) { // Checking whether there is enough argument
return -1;
}
av_register_all(); //Initialize CODEC
avformat_network_init();
av_init_packet (&avPkt);
if (avformat_open_input (&pFormatCtxt, argv[1],NULL,NULL)!= 0 ){ //Opening File
return -2;
}
if(avformat_find_stream_info (pFormatCtxt,NULL) < 0){ //Get Streams Info
return -3;
}
AVStream *stream = NULL;
//av_read_play (pFormatCtxt); //open streams
for (int i = 0; i < pFormatCtxt->nb_streams ; i++) { //Find Audio Stream
if (pFormatCtxt->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO){
audioStream =i;
}
}
aCodecCtxt = pFormatCtxt ->streams [audioStream]->codec; // opening decoder
aCodec = avcodec_find_decoder( pFormatCtxt->streams [audioStream] ->codec->codec_id);
if (!aCodec) {
return -8;
}
if (avcodec_open2(aCodecCtxt,aCodec,NULL)!=0) {
return -9;
}
int cnt = 0;
while(av_read_frame(pFormatCtxt,&avPkt) >= 0 ){
if (avPkt.stream_index == audioStream){
int check = 0;
int result = avcodec_decode_audio4 (aCodecCtxt,decode_frame,&check, &avPkt);
cout << "Decoded : "<< (int) decode_frame->data[0] <<", "<< "Check : " << check << ", Format :" << decode_frame->format <<" " << decode_frame->linesize[0]<< " "<<cnt <<endl;
}
av_free_packet(&avPkt);
cnt++;
}
return aCodec ->id;
}

Answer 1

You're doing it right.
The data that you decode contain at the pointer decode_frame->data[0]. Data size in bytes is decode_frame->linesize[0], the number of audio samples is decode_frame->nb_samples.
Thus, you can copy the audio data into your own buffer as follows:
memcpy(OutputBuffer, decode_frame->data[0], decode_frame->linesize[0]);

Answer 2

You can try using ffms2 which will directly give you decoded audio sample. It internally used ffmpeg/libav. So you don't have to worry about decoding stuff.
https://code.google.com/p/ffmpegsource/