fs2open.github.com/code/sound/ffmpeg/FFmpegAudioReader.cpp

#include "FFmpegAudioReader.h"

namespace
{
class AVPacketScope
{
	AVPacket* _packet;
public:
	explicit AVPacketScope(AVPacket* av_packet)
		: _packet(av_packet) {
	}

	~AVPacketScope() {
		av_packet_unref(_packet);
	}
};
#if LIBAVCODEC_VERSION_INT < AV_VERSION_INT(57, 24, 100)
// This version doesn't have the new packet alloc API

AVPacket *av_packet_alloc()
{
	auto packet = (AVPacket*)av_mallocz(sizeof(AVPacket));
	av_packet_unref(packet);
	return packet;
}

AVPacket *av_packet_clone(AVPacket *src)
{
	auto ret = av_packet_alloc();
	av_packet_ref(ret, src);
	return ret;
}

void av_packet_free(AVPacket **pkt)
{
	av_packet_unref(*pkt);
	av_freep(pkt);
}
#endif
} // namespace

namespace sound {
namespace ffmpeg {
FFmpegAudioReader::FFmpegAudioReader(AVFormatContext* av_format_context, AVCodecContext* codec_ctx,
                                     int stream_idx) : _stream_idx(stream_idx),
                                                       _format_ctx(av_format_context),
                                                       _codec_ctx(codec_ctx) {
}

bool FFmpegAudioReader::readFrame(AVFrame* decode_frame) {
	// FFmpeg 3.1 and onwards has a new, better packet handling API but that version is relatively new so we still need
	// to support the earlier API. The compatibility code can be removed once the new version is supported by most platforms

#if LIBAVCODEC_VERSION_INT > AV_VERSION_INT(57, 24, 255)
	// Process pending frames
	auto pending_res = avcodec_receive_frame(_codec_ctx, decode_frame);

	if (pending_res == 0) {
		// Got a frame
		return true;
	}
	if (pending_res == AVERROR_EOF) {
		// No more frames available
		return false;
	}

	if (pending_res != AVERROR(EAGAIN)) {
		// Unknown error.
		return false;
	}
#else
	if (_currentPacket != nullptr) {
		// Got some data left
		int finishedFrame = 0;
		auto bytes_read = avcodec_decode_audio4(_codec_ctx, decode_frame, &finishedFrame, _currentPacket);

		if (bytes_read < 0) {
			// Error!
			return false;
		}

		_currentPacket->data += bytes_read;
		_currentPacket->size -= bytes_read;

		if (_currentPacket->size <= 0) {
			// Done with this packet
			av_packet_free(&_currentPacket);
		}

		if (finishedFrame) {
			return true;
		}
	}
#endif

	AVPacket packet;
	while (av_read_frame(_format_ctx, &packet) >= 0) {
		AVPacketScope packet_scope(&packet);
		if (packet.stream_index == _stream_idx) {
#if LIBAVCODEC_VERSION_INT > AV_VERSION_INT(57, 24, 255)
			auto res = avcodec_send_packet(_codec_ctx, &packet);

			if (res != 0) {
				// Error or EOF
				return false;
			}

			res = avcodec_receive_frame(_codec_ctx, decode_frame);

			if (res == 0) {
				// Got a frame
				return true;
			}
			if (res == AVERROR_EOF) {
				// No more frames available
				return false;
			}

			if (res != AVERROR(EAGAIN)) {
				// Unknown error.
				return false;
			}
			// EGAIN was returned, send new input
#else
			int finishedFrame = 0;
			auto bytes_read = avcodec_decode_audio4(_codec_ctx, decode_frame, &finishedFrame, &packet);

			if (bytes_read < packet.size) {
				// Not all data was read
				packet.data += bytes_read;
				packet.size -= bytes_read;

				_currentPacket = av_packet_clone(&packet);
			}

			if (finishedFrame) {
				return true;
			}

			if (bytes_read < 0) {
				// Error
				return false;
			}
#endif
		}
	}

#if LIBAVCODEC_VERSION_INT > AV_VERSION_INT(57, 24, 255)
	// Flush decoder
	if (avcodec_send_packet(_codec_ctx, nullptr) != 0) {
		return false;
	}

	auto flush_res = avcodec_receive_frame(_codec_ctx, decode_frame);

	if (flush_res == 0) {
		// Got a frame
		return true;
	}
#else
	AVPacket nullPacket;
	memset(&nullPacket, 0, sizeof(nullPacket));
	nullPacket.data = nullptr;
	nullPacket.size = 0;

	int finishedFrame = 1;
	auto err = avcodec_decode_audio4(_codec_ctx, decode_frame, &finishedFrame, &nullPacket);

	if (finishedFrame && err >= 0) {
		return true;
	}
#endif

	// If we are here then read_frame reached the end or returned an error
	return false;
}
FFmpegAudioReader::~FFmpegAudioReader() {
#if LIBAVCODEC_VERSION_INT <= AV_VERSION_INT(57, 24, 255)
    if (_currentPacket != nullptr) {
		av_packet_unref(_currentPacket);
		av_packet_free(&_currentPacket);
	}
#endif
}

} // namespace ffmpeg
} // namespace sound