Decode .wav file and write it into another file using ffmpeg - objective-c

Question

How to decode a .wav file and write it into another file using ffmpeg?
I got decoded data by this piece of code:
-(void)audioDecode:(const char *)outfilename inFileName:(const char *)filename
{
const char* input_filename=filename;
//avcodec_register_all();
av_register_all();
avcodec_register_all();
// av_register_all();
//av_ini
// AVFormatContext* container=avformat_alloc_context();
// if(avformat_open_input(&container,filename,NULL,NULL)<0){
// NSLog(#"Could not open file");
// }
AVCodec *codec;
AVCodecContext *c= NULL;
int len;
FILE *f, *outfile;
uint8_t inbuf[AUDIO_INBUF_SIZE + FF_INPUT_BUFFER_PADDING_SIZE];
AVPacket avpkt;
AVFrame *decoded_frame = NULL;
av_init_packet(&avpkt);
printf("Decode audio file %s to %s\n", filename, outfilename);
avcodec_register_all();
AVFrame* frame = av_frame_alloc();
if (!frame)
{
fprintf(stderr, "Could not allocate audio frame\n");
exit(1);
}
AVFormatContext* formatContext = NULL;
/* Opening the file, and check if it has opened */
if (avformat_open_input(&formatContext, filename, NULL, NULL) != 0)
{
av_frame_free(&frame);
NSLog(#"Could not open file");
}
if (avformat_find_stream_info(formatContext, NULL) < 0)
{
av_frame_free(&frame);
avformat_close_input(&formatContext);
NSLog(#"Error finding the stream info");
}
outfile = fopen(outfilename, "wb");
if (!outfile) {
av_free(c);
exit(1);
}
/* Find the audio Stream, if no audio stream are found, clean and exit */
AVCodec* cdc = NULL;
int streamIndex = av_find_best_stream(formatContext, AVMEDIA_TYPE_AUDIO, -1, -1, &cdc, 0);
if (streamIndex < 0)
{
av_frame_free(&frame);
avformat_close_input(&formatContext);
NSLog(#"Could not find any audio stream in the file");
exit(1);
}
/* Open the audio stream to read data in audioStream */
AVStream* audioStream = formatContext->streams[streamIndex];
/* Initialize the codec context */
AVCodecContext* codecContext = audioStream->codec;
codecContext->codec = cdc;
/* Open the codec, and verify if it has opened */
if (avcodec_open2(codecContext, codecContext->codec, NULL) != 0)
{
av_frame_free(&frame);
avformat_close_input(&formatContext);
NSLog(#"Couldn't open the context with the decoder");
exit(1);
}
/* Initialize buffer to store compressed packets */
AVPacket readingPacket;
av_init_packet(&readingPacket);
int lenght = 1;
long long int chunk = ((formatContext->bit_rate)*lenght/8);
int j=0;
int count = 0;
//audioChunk output;
while(av_read_frame(formatContext, &readingPacket)==0){
//if((count+readingPacket.size)>start){
if(readingPacket.stream_index == audioStream->index){
AVPacket decodingPacket = readingPacket;
// Audio packets can have multiple audio frames in a single packet
while (decodingPacket.size > 0){
// Try to decode the packet into a frame
// Some frames rely on multiple packets, so we have to make sure the frame is finished before
// we can use it
int gotFrame = 0;
int result = avcodec_decode_audio4(codecContext, frame, &gotFrame, &decodingPacket);
count += result;
if (result >= 0 && gotFrame)
{
decodingPacket.size -= result;
decodingPacket.data += result;
int a;
for(int i=0;i<result-1;i++){
fwrite(frame->data[0], 1, decodingPacket.size, outfile);
// *(output.data+j)=frame->data[0][i];
//
j++;
if(j>=chunk) break;
}
// We now have a fully decoded audio frame
}
else
{
decodingPacket.size = 0;
decodingPacket.data = NULL;
}
// if(j>=chunk) break;
}
}
// }else count+=readingPacket.size;
//
// // To prevent memory leak, must free packet.
// av_free_packet(&readingPacket);
// if(j>=chunk) break;
}
fclose(outfile);
But the file is created with zero bytes. I don't know what's wrong with this code. And I got one more error: "Format adp detected only with low score of 25, misdetection possible!"