FFMpeg audio samples extraction

FFMpegPlayer.cpp

AVPacket packet;
AVCodecContext *codecContext = NULL;
AVFormatContext *formatContext;
AVFrame *frame = NULL;
SwrContext *swrContext = NULL;

int audio_stream_index = -1;
int ret;
uint8_t *localBuffer;

int out_sample_rate = 48000;

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);
	
	// 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
	swr_alloc_set_opts(swrContext, AV_CH_LAYOUT_STEREO, AV_SAMPLE_FMT_FLT, out_sample_rate,
	                   codecContext->channel_layout, codecContext->sample_fmt, codecContext->sample_rate, 0,
	                   NULL);
	swr_init(swrContext);
	
	return 0;
}

void FFMpegPlayer::seek(long seekPosition)
{
	av_seek_frame(formatContext, -1, seekPosition, 0);
}

void FFMpegPlayer::getPcmFloat(float *buffer)
{
	// init :
	int i, ch, dataSize;
	bool extraxted = false;
	float sample = 0;
	
	// extract :
	while (!extraxted && av_read_frame(formatContext, &packet) >= 0)
	{
		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);
				
				// resampling:
				int out_samples = (int) av_rescale_rnd(
					swr_get_delay(swrContext, codecContext->sample_rate) + frame->nb_samples,
					out_sample_rate,
					codecContext->sample_rate,
					AV_ROUND_UP);
				av_samples_alloc(&localBuffer, NULL, 2, out_samples, AV_SAMPLE_FMT_FLT, 0);
				int numberSampleOutputPerChannel = swr_convert(swrContext,
					  				&localBuffer, out_samples,
					   				(const uint8_t **) frame->extended_data, frame->nb_samples);

				// position in microseconds:
				long position = 1000000 * (packet.pts * ((float) stream->time_base.num / stream->time_base.den));
				LOGD("position = %li", position);
				
				// copy from localBuffer to buffer:
				int a = 0;
				for (i = 0; i < numberSampleOutputPerChannel; i++)
				{
					for (ch = 0; ch < codecContext->channels; ch++)
					{
						memcpy(&sample, &localBuffer[(codecContext->channels * i + ch) * dataSize], dataSize);
						buffer[a] = sample;
						a++;
					}
				}
				
				av_freep(&localBuffer);
				
				// exit extract:
				extraxted = true;
			}
		}
	}
}

void FFMpegPlayer::releaseFFmpeg()
{
	packet.data = NULL;
	packet.size = 0;
	avcodec_free_context(&codecContext);
	swr_free(&swrContext);
}