FFMpeg: extracting audio frames with avcodec creates noise - c++

Question

In my Android app, I implemented the FFMpeg library, and try to use it so I can extract audio samples from an audio file on the fly.
Here is what I did (I simplified the code here so it's easier to read):
AVPacket packet;
AVCodecContext *codecContext = NULL;
AVFormatContext *formatContext;
AVFrame *frame = NULL;
SwrContext *swrContext;
int audio_stream_index = -1;
int ret;
uint8_t *localBuffer;
int FFMpegPlayer::createFFmpeg(const char *filename)
{
int ret;
AVCodec *dec;
frame = av_frame_alloc();
av_register_all();
avformat_open_input(&formatContext, filename, NULL, NULL))
avformat_find_stream_info(formatContext, NULL))
// select the audio stream
audio_stream_index = av_find_best_stream(formatContext, AVMEDIA_TYPE_AUDIO, -1, -1, &dec, 0);
// create decoding context
codecContext = avcodec_alloc_context3(dec);
avcodec_parameters_to_context(codecContext, formatContext->streams[audio_stream_index]->codecpar);
av_opt_set_int(codecContext, "refcounted_frames", 1, 0);
// init the audio decoder
avcodec_open2(codecContext, dec, NULL))
swrContext = swr_alloc();
// we assume here that the audio file is a 44100 Hz stereo audio file
localBuffer = (uint8_t *) av_malloc(44100 * 2);
swr_alloc_set_opts(swrContext, AV_CH_LAYOUT_STEREO, AV_SAMPLE_FMT_FLT, codecContext->sample_rate,
codecContext->channel_layout, codecContext->sample_fmt, codecContext->sample_rate, 0,
NULL);
swr_init(swrContext);
return 0;
}
void FFMpegPlayer::getPcmFloat(float *buffer)
{
// init :
int i, ch, dataSize;
bool extraxted = false;
float sample = 0;
// extract :
while (av_read_frame(formatContext, &packet) >= 0 && !extraxted)
{
if (packet.stream_index == audio_stream_index)
{
// send the packet with the compressed data to the decoder
ret = avcodec_send_packet(codecContext, &packet);
// read all the output frames (in general there may be any number of them
while (ret >= 0)
{
ret = avcodec_receive_frame(codecContext, frame);
if (ret == AVERROR(EAGAIN))
{
LOGW("AVERROR(EAGAIN)\n");
break;
}
else if (ret == AVERROR_EOF)
{
LOGW("AVERROR_EOF\n");
break;
}
dataSize = av_get_bytes_per_sample(codecContext->sample_fmt);
swr_convert(swrContext, &localBuffer, 44100 * 2, (const uint8_t **) frame->data, frame->nb_samples);
int a = 0;
for (i = 0; i < frame->nb_samples; i++)
{
for (ch = 0; ch < codecContext->channels; ch++)
{
memcpy(&sample, &localBuffer[(codecContext->channels * i + ch) * dataSize], dataSize);
buffer[a] = sample;
a++;
}
}
// exit extract:
extraxted = true;
}
}
}
}
Anytime I need audio samples, I call the getPcmFloat() function.
Thanks to that code, I can clearly listen to the audio file.
The problem is: I have some crackling in the sound, and I have no idea where it comes from, or how to fix it.
Does anyone know how to get the exact frames whithout glitches?
Thanks for your help.