SDL Audio - Plays only Static Noise - c

Question

Im having an issue with playing audio.
Im new to the SDL World of things so im learning from a tutorial.
http://dranger.com/ffmpeg/tutorial03.html
As far as audio goes, i have exactly what he put down and didnt get the result he says I should get. In the end of the lesson he specifies that the audio should play normally. However all i get is excessively loud static noise. This leads me to believe that the packets arent being read correctly. However I have no idea how to debug or look for the issue.
Here is my main loop for parsing the packets:
while (av_read_frame(pFormatCtx, &packet) >= 0) {
if (packet.stream_index == videoStream) {
avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
if (frameFinished){
AVPicture pict;
pict.data[0] = yPlane;
pict.data[1] = uPlane;
pict.data[2] = vPlane;
pict.linesize[0] = pCodecCtx->width;
pict.linesize[1] = uvPitch;
pict.linesize[2] = uvPitch;
sws_scale(sws_ctx,
pFrame->data, pFrame->linesize,
0, pCodecCtx->height,
pict.data, pict.linesize);
//SDL_UnlockTexture(bmp);
SDL_UpdateYUVTexture(bmp, 0,
yPlane, pCodecCtx->width,
uPlane, uvPitch,
vPlane, uvPitch);
SDL_RenderClear(renderer);
SDL_RenderCopy(renderer, bmp, NULL, NULL);
SDL_RenderPresent(renderer);
av_free_packet(&packet);
}
}
else if (packet.stream_index == audioStream) {
packet_queue_put(&audioq, &packet);
}
else
av_free_packet(&packet);
SDL_PollEvent(&event);
switch (event.type) {
case SDL_QUIT:
quit = 1;
SDL_DestroyTexture(bmp);
SDL_DestroyRenderer(renderer);
SDL_DestroyWindow(screen);
SDL_Quit();
exit(0);
break;
default:
break;
}
}
this is my initialization of the audio device :
aCodecCtxOrig = pFormatCtx->streams[audioStream]->codec;
aCodec = avcodec_find_decoder(aCodecCtxOrig->codec_id);
if (!aCodec) {
fprintf(stderr, "Unsupported codec!\n");
return -1;
}
// Copy context
aCodecCtx = avcodec_alloc_context3(aCodec);
if (avcodec_copy_context(aCodecCtx, aCodecCtxOrig) != 0) {
fprintf(stderr, "Couldn't copy codec context");
return -1; // Error copying codec context
}
wanted_spec.freq = aCodecCtx->sample_rate;
wanted_spec.format = AUDIO_U16SYS;
wanted_spec.channels = aCodecCtx->channels;
wanted_spec.silence = 0;
wanted_spec.samples = SDL_AUDIO_BUFFER_SIZE;
wanted_spec.callback = audio_callback;
wanted_spec.userdata = aCodecCtx;
if (SDL_OpenAudio( &wanted_spec, &spec) < 0) {
fprintf(stderr, "SDL_OpenAudio: %s\n", SDL_GetError());
return -1;
}
avcodec_open2(aCodecCtx, aCodec, NULL);
// audio_st = pFormatCtx->streams[index]
packet_queue_init(&audioq);
SDL_PauseAudio(0);
The Call back (same as the tutorial):|
void audio_callback(void *userdata, Uint8 *stream, int len) {
AVCodecContext *aCodecCtx = (AVCodecContext *)userdata;
int len1, audio_size;
static uint8_t audio_buf[(MAX_AUDIO_FRAME_SIZE * 3) / 2];
static unsigned int audio_buf_size = 0;
static unsigned int audio_buf_index = 0;
while (len > 0) {
if (audio_buf_index >= audio_buf_size) {
/* We have already sent all our data; get more */
audio_size = audio_decode_frame(aCodecCtx, audio_buf, sizeof(audio_buf));
if (audio_size < 0) {
/* If error, output silence */
audio_buf_size = 1024; // arbitrary?
memset(audio_buf, 0, audio_buf_size);
}
else {
audio_buf_size = audio_size;
}
audio_buf_index = 0;
}
len1 = audio_buf_size - audio_buf_index;
if (len1 > len)
len1 = len;
memcpy(stream, (uint8_t *)audio_buf + audio_buf_index, len1);
len -= len1;
stream += len1;
audio_buf_index += len1;
}
}

Answer 1

I also had same problem when I learn tutorial 3. The comments by pprahul in https://github.com/mpenkov/ffmpeg-tutorial/issues/11 solve my problem when playing .MPG file with mp2 format audio. But the problem still occur when I play .MP4 file with AAC format audio.
A snapshot of that comment is to set the decode format manually， by
//after get the AVCodecContext *codecCtx(aCodecCtx in tutorial).
if (codecCtx->sample_fmt == AV_SAMPLE_FMT_S16P) {
codecCtx->request_sample_fmt = AV_SAMPLE_FMT_S16;
}
//...
It seems that the problem will not occur with early version of FFmpeg (1.01 and below).