scummvm/video/mpegps_decoder.cpp

/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 */

#include "audio/audiostream.h"
#include "audio/decoders/raw.h"
#include "common/endian.h"
#include "common/stream.h"
#include "common/system.h"
#include "common/textconsole.h"
#include "graphics/yuv_to_rgb.h"

#include "video/mpegps_decoder.h"

// The demuxing code is based on libav's demuxing code

namespace Video {

#define PACK_START_CODE          0x1BA
#define SYSTEM_HEADER_START_CODE 0x1BB

#define PROGRAM_STREAM_MAP       0x1BC
#define PRIVATE_STREAM_1         0x1BD
#define PADDING_STREAM           0x1BE
#define PRIVATE_STREAM_2         0x1BF

MPEGPSDecoder::MPEGPSDecoder() {
	_stream = 0;
	memset(_psmESType, 0, 256);
}

MPEGPSDecoder::~MPEGPSDecoder() {
	close();
}

bool MPEGPSDecoder::loadStream(Common::SeekableReadStream *stream) {
	close();

	_stream = stream;

	if (!addFirstVideoTrack()) {
		close();
		return false;
	}

	_stream->seek(0);
	return true;
}

void MPEGPSDecoder::close() {
	VideoDecoder::close();

	delete _stream;
	_stream = 0;

	_streamMap.clear();

	memset(_psmESType, 0, 256);
}

void MPEGPSDecoder::readNextPacket() {
	if (_stream->eos())
		return;

	for (;;) {
		int32 startCode;
		uint32 pts, dts;
		int size = readNextPacketHeader(startCode, pts, dts);

		if (size < 0) {
			// End of stream
			for (TrackListIterator it = getTrackListBegin(); it != getTrackListEnd(); it++)
				if ((*it)->getTrackType() == Track::kTrackTypeVideo)
					((MPEGVideoTrack *)*it)->setEndOfTrack();
			return;
		}

		MPEGStream *stream = 0;
		Common::SeekableReadStream *packet = _stream->readStream(size);

		if (_streamMap.contains(startCode)) {
			// We already found the stream
			stream = _streamMap[startCode];
		} else {
			// We haven't seen this before

			if (startCode == 0x1BD) {
				// Private stream 1
				PrivateStreamType streamType = detectPrivateStreamType(packet);

				packet->seek(0);

				switch (streamType) {
				case kPrivateStreamPS2Audio: {
					// PS2 Audio stream
					PS2AudioTrack *audioTrack = new PS2AudioTrack(packet);
					stream = audioTrack;
					_streamMap[startCode] = audioTrack;
					addTrack(audioTrack);
					break;
				}
				default:
					// Unknown (silently ignore)
					break;
				}
			} if (startCode >= 0x1E0 && startCode <= 0x1EF) {
				// Video stream
				// TODO: Multiple video streams
			} else if (startCode >= 0x1C0 && startCode <= 0x1DF) {
#ifdef USE_MAD
				// MPEG Audio stream
				MPEGAudioTrack *audioTrack = new MPEGAudioTrack(packet);
				stream = audioTrack;
				_streamMap[startCode] = audioTrack;
				addTrack(audioTrack);
#endif
			}
		}

		if (stream) {
			bool done = stream->sendPacket(packet, pts, dts);

			if (done && stream->getStreamType() == MPEGStream::kStreamTypeVideo)
				return;
		} else {
			delete packet;
		}
	}
}

#define MAX_SYNC_SIZE 100000

int MPEGPSDecoder::findNextStartCode(uint32 &size) {
	size = MAX_SYNC_SIZE;
	int32 state = 0xFF;

	while (size > 0) {
		byte v = _stream->readByte();

		if (_stream->eos())
			return -1;

		size--;

		if (state == 0x1)
			return ((state << 8) | v) & 0xFFFFFF;

		state = ((state << 8) | v) & 0xFFFFFF;
	}

	return -1;
}

int MPEGPSDecoder::readNextPacketHeader(int32 &startCode, uint32 &pts, uint32 &dts) {
	for (;;) {
		uint32 size;
		startCode = findNextStartCode(size);

		if (_stream->eos())
			return -1;

		if (startCode < 0)
			continue;

		uint32 lastSync = _stream->pos();

		if (startCode == PACK_START_CODE || startCode == SYSTEM_HEADER_START_CODE)
			continue;

		int length = _stream->readUint16BE();

		if (startCode == PADDING_STREAM || startCode == PRIVATE_STREAM_2) {
			_stream->skip(length);
			continue;
		}

		if (startCode == PROGRAM_STREAM_MAP) {
			parseProgramStreamMap(length);
			continue;
		}

		// Find matching stream
		if (!((startCode >= 0x1C0 && startCode <= 0x1DF) ||
				(startCode >= 0x1E0 && startCode <= 0x1EF) ||
				startCode == 0x1BD || startCode == 0x1FD))
			continue;

		// Stuffing
		byte c;
		for (;;) {
			if (length < 1) {
				_stream->seek(lastSync);
				continue;
			}

			c = _stream->readByte();
			length--;

			// XXX: for mpeg1, should test only bit 7
			if (c != 0xFF)
				break;
		}

		if ((c & 0xC0) == 0x40) {
			// Buffer scale and size
			_stream->readByte();
			c = _stream->readByte();
			length -= 2;
		}

		pts = 0xFFFFFFFF;
		dts = 0xFFFFFFFF;

		if ((c & 0xE0) == 0x20) {
			dts = pts = readPTS(c);
			length -= 4;

			if (c & 0x10) {
				dts = readPTS(-1);
				length -= 5;
			}
		} else if ((c & 0xC0) == 0x80) {
			// MPEG-2 PES
			byte flags = _stream->readByte();
			int headerLength = _stream->readByte();
			length -= 2;

			if (headerLength > length) {
				_stream->seek(lastSync);
				continue;
			}

			length -= headerLength;

			if (flags & 0x80) {
				dts = pts = readPTS(-1);
				headerLength -= 5;

				if (flags & 0x40) {
					dts = readPTS(-1);
					headerLength -= 5;
				}
			}

			if (flags & 0x3F && headerLength == 0) {
				flags &= 0xC0;
				warning("Further flags set but no bytes left");
			}

			if (flags & 0x01) { // PES extension
				byte pesExt =_stream->readByte();
				headerLength--;

				// Skip PES private data, program packet sequence
				int skip = (pesExt >> 4) & 0xB;
				skip += skip & 0x9;

				if (pesExt & 0x40 || skip > headerLength) {
					warning("pesExt %x is invalid", pesExt);
					pesExt = skip = 0;
				} else {
					_stream->skip(skip);
					headerLength -= skip;
				}

				if (pesExt & 0x01) { // PES extension 2
					byte ext2Length = _stream->readByte();
					headerLength--;

					if ((ext2Length & 0x7F) != 0) {
						byte idExt = _stream->readByte();

						if ((idExt & 0x80) == 0)
							startCode = (startCode & 0xFF) << 8;

						headerLength--;
					}
				}
			}

			if (headerLength < 0) {
				_stream->seek(lastSync);
				continue;
			}

			_stream->skip(headerLength);
		} else if (c != 0xF) {
			continue;
		}

		if (length < 0) {
			_stream->seek(lastSync);
			continue;
		}

		return length;
	}
}

uint32 MPEGPSDecoder::readPTS(int c) {
	byte buf[5];

	buf[0] = (c < 0) ? _stream->readByte() : c;
	_stream->read(buf + 1, 4);

	return ((buf[0] & 0x0E) << 29) | ((READ_BE_UINT16(buf + 1) >> 1) << 15) | (READ_BE_UINT16(buf + 3) >> 1);
}

void MPEGPSDecoder::parseProgramStreamMap(int length) {
	_stream->readByte();
	_stream->readByte();

	// skip program stream info
	_stream->skip(_stream->readUint16BE());

	int esMapLength = _stream->readUint16BE();

	while (esMapLength >= 4) {
		byte type = _stream->readByte();
		byte esID = _stream->readByte();
		uint16 esInfoLength = _stream->readUint16BE();

		// Remember mapping from stream id to stream type
		_psmESType[esID] = type;

		// Skip program stream info
        _stream->skip(esInfoLength);

		esMapLength -= 4 + esInfoLength;
	}

	_stream->readUint32BE(); // CRC32
}

bool MPEGPSDecoder::addFirstVideoTrack() {
	for (;;) {
		int32 startCode;
		uint32 pts, dts;
		int size = readNextPacketHeader(startCode, pts, dts);

		// End of stream? We failed
		if (size < 0)
			return false;

		if (startCode >= 0x1E0 && startCode <= 0x1EF) {
			// Video stream
			// Can be MPEG-1/2 or MPEG-4/h.264. We'll assume the former and
			// I hope we never need the latter.
			Common::SeekableReadStream *firstPacket = _stream->readStream(size);
			MPEGVideoTrack *track = new MPEGVideoTrack(firstPacket, getDefaultHighColorFormat());
			addTrack(track);
			_streamMap[startCode] = track;
			delete firstPacket;
			break;
		}

		_stream->skip(size);
	}

	return true;
}

MPEGPSDecoder::PrivateStreamType MPEGPSDecoder::detectPrivateStreamType(Common::SeekableReadStream *packet) {
	packet->seek(4);

	if (packet->readUint32BE() == MKTAG('S', 'S', 'h', 'd'))
		return kPrivateStreamPS2Audio;

	return kPrivateStreamUnknown;
}

MPEGPSDecoder::MPEGVideoTrack::MPEGVideoTrack(Common::SeekableReadStream *firstPacket, const Graphics::PixelFormat &format) {
	_endOfTrack = false;
	_curFrame = -1;
	_nextFrameStartTime = Audio::Timestamp(0, 27000000); // 27 MHz timer

	findDimensions(firstPacket, format);

#ifdef USE_MPEG2
	_mpegDecoder = mpeg2_init();

	if (!_mpegDecoder)
		error("Could not initialize libmpeg2");

	_mpegInfo = mpeg2_info(_mpegDecoder);
#endif
}

MPEGPSDecoder::MPEGVideoTrack::~MPEGVideoTrack() {
#ifdef USE_MPEG2
	mpeg2_close(_mpegDecoder);
#endif

	_surface->free();
	delete _surface;
}

uint16 MPEGPSDecoder::MPEGVideoTrack::getWidth() const {
	return _surface->w;
}

uint16 MPEGPSDecoder::MPEGVideoTrack::getHeight() const {
	return _surface->h;
}

Graphics::PixelFormat MPEGPSDecoder::MPEGVideoTrack::getPixelFormat() const {
	return _surface->format;
}

const Graphics::Surface *MPEGPSDecoder::MPEGVideoTrack::decodeNextFrame() {
	return _surface;
}

bool MPEGPSDecoder::MPEGVideoTrack::sendPacket(Common::SeekableReadStream *packet, uint32 pts, uint32 dts) {
#ifdef USE_MPEG2
	// Decode as much as we can out of this packet
	uint32 size = 0xFFFFFFFF;
	mpeg2_state_t state;
	bool foundFrame = false;

	do {
		state = mpeg2_parse(_mpegDecoder);

		switch (state) {
		case STATE_BUFFER:
			size = packet->read(_buffer, BUFFER_SIZE);
			mpeg2_buffer(_mpegDecoder, _buffer, _buffer + size);
			break;
		case STATE_SLICE:
		case STATE_END:
			foundFrame = true;
			_curFrame++;

			if (_mpegInfo->display_fbuf) {
				const mpeg2_sequence_t *sequence = _mpegInfo->sequence;
				_nextFrameStartTime = _nextFrameStartTime.addFrames(sequence->frame_period);

				YUVToRGBMan.convert420(_surface, Graphics::YUVToRGBManager::kScaleITU, _mpegInfo->display_fbuf->buf[0],
						_mpegInfo->display_fbuf->buf[1], _mpegInfo->display_fbuf->buf[2], sequence->picture_width,
						sequence->picture_height, sequence->width, sequence->chroma_width);
			}
			break;
		default:
			break;
		}
	} while (size != 0);
#endif

	delete packet;

#ifdef USE_MPEG2
	return foundFrame;
#else
	return true;
#endif
}

void MPEGPSDecoder::MPEGVideoTrack::findDimensions(Common::SeekableReadStream *firstPacket, const Graphics::PixelFormat &format) {
	// First, check for the picture start code
	if (firstPacket->readUint32BE() != 0x1B3)
		error("Failed to detect MPEG sequence start");

	// This is part of the bitstream, but there's really no purpose
	// to use Common::BitStream just for this: 12 bits width, 12 bits
	// height
	uint16 width = firstPacket->readByte() << 4;
	uint16 height = firstPacket->readByte();
	width |= (height & 0xF0) >> 4;
	height = ((height & 0xF) << 8) | firstPacket->readByte();

	debug(0, "MPEG dimensions: %dx%d", width, height);

	_surface = new Graphics::Surface();
	_surface->create(width, height, format);

	firstPacket->seek(0);
}

#ifdef USE_MAD

// The audio code here is almost entirely based on what we do in mp3.cpp

MPEGPSDecoder::MPEGAudioTrack::MPEGAudioTrack(Common::SeekableReadStream *firstPacket) {
	// The MAD_BUFFER_GUARD must always contain zeros (the reason
	// for this is that the Layer III Huffman decoder of libMAD
	// may read a few bytes beyond the end of the input buffer).
	memset(_buf + BUFFER_SIZE, 0, MAD_BUFFER_GUARD);

	_state = MP3_STATE_INIT;
	_audStream = 0;

	// Find out our audio parameters
	initStream(firstPacket);

	while (_state != MP3_STATE_EOS)
		readHeader(firstPacket);

	_audStream = Audio::makeQueuingAudioStream(_frame.header.samplerate, MAD_NCHANNELS(&_frame.header) == 2);

	deinitStream();

	firstPacket->seek(0);
	_state = MP3_STATE_INIT;
}

MPEGPSDecoder::MPEGAudioTrack::~MPEGAudioTrack() {
	deinitStream();
	delete _audStream;
}

static inline int scaleSample(mad_fixed_t sample) {
	// round
	sample += (1L << (MAD_F_FRACBITS - 16));

	// clip
	if (sample > MAD_F_ONE - 1)
		sample = MAD_F_ONE - 1;
	else if (sample < -MAD_F_ONE)
		sample = -MAD_F_ONE;

	// quantize and scale to not saturate when mixing a lot of channels
	return sample >> (MAD_F_FRACBITS + 1 - 16);
}

bool MPEGPSDecoder::MPEGAudioTrack::sendPacket(Common::SeekableReadStream *packet, uint32 pts, uint32 dts) {
	while (_state != MP3_STATE_EOS)
		decodeMP3Data(packet);

	_state = MP3_STATE_READY;
	delete packet;
	return true;
}

Audio::AudioStream *MPEGPSDecoder::MPEGAudioTrack::getAudioStream() const {
	return _audStream;
}

void MPEGPSDecoder::MPEGAudioTrack::initStream(Common::SeekableReadStream *packet) {
	if (_state != MP3_STATE_INIT)
		deinitStream();

	// Init MAD
	mad_stream_init(&_stream);
	mad_frame_init(&_frame);
	mad_synth_init(&_synth);

	// Reset the stream data
	packet->seek(0, SEEK_SET);

	// Update state
	_state = MP3_STATE_READY;

	// Read the first few sample bytes
	readMP3Data(packet);
}

void MPEGPSDecoder::MPEGAudioTrack::deinitStream() {
	if (_state == MP3_STATE_INIT)
		return;

	// Deinit MAD
	mad_synth_finish(&_synth);
	mad_frame_finish(&_frame);
	mad_stream_finish(&_stream);

	_state = MP3_STATE_EOS;
}

void MPEGPSDecoder::MPEGAudioTrack::readMP3Data(Common::SeekableReadStream *packet) {
	uint32 remaining = 0;

	// Give up immediately if we already used up all data in the stream
	if (packet->eos()) {
		_state = MP3_STATE_EOS;
		return;
	}

	if (_stream.next_frame) {
		// If there is still data in the MAD stream, we need to preserve it.
		// Note that we use memmove, as we are reusing the same buffer,
		// and hence the data regions we copy from and to may overlap.
		remaining = _stream.bufend - _stream.next_frame;
		assert(remaining < BUFFER_SIZE);	// Paranoia check
		memmove(_buf, _stream.next_frame, remaining);
	}

	memset(_buf + remaining, 0, BUFFER_SIZE - remaining);

	// Try to read the next block
	uint32 size = packet->read(_buf + remaining, BUFFER_SIZE - remaining);
	if (size == 0) {
		_state = MP3_STATE_EOS;
		return;
	}

	// Feed the data we just read into the stream decoder
	_stream.error = MAD_ERROR_NONE;
	mad_stream_buffer(&_stream, _buf, size + remaining);
}

void MPEGPSDecoder::MPEGAudioTrack::readHeader(Common::SeekableReadStream *packet) {
	if (_state != MP3_STATE_READY)
		return;

	// If necessary, load more data into the stream decoder
	if (_stream.error == MAD_ERROR_BUFLEN)
		readMP3Data(packet);

	while (_state != MP3_STATE_EOS) {
		_stream.error = MAD_ERROR_NONE;

		// Decode the next header. Note: mad_frame_decode would do this for us, too.
		// However, for seeking we don't want to decode the full frame (else it would
		// be far too slow). Hence we perform this explicitly in a separate step.
		if (mad_header_decode(&_frame.header, &_stream) == -1) {
			if (_stream.error == MAD_ERROR_BUFLEN) {
				readMP3Data(packet);  // Read more data
				continue;
			} else if (MAD_RECOVERABLE(_stream.error)) {
				debug(6, "MPEGAudioTrack::readHeader(): Recoverable error in mad_header_decode (%s)", mad_stream_errorstr(&_stream));
				continue;
			} else {
				warning("MPEGAudioTrack::readHeader(): Unrecoverable error in mad_header_decode (%s)", mad_stream_errorstr(&_stream));
				break;
			}
		}

		break;
	}

	if (_stream.error != MAD_ERROR_NONE)
		_state = MP3_STATE_EOS;
}

void MPEGPSDecoder::MPEGAudioTrack::decodeMP3Data(Common::SeekableReadStream *packet) {
	if (_state == MP3_STATE_INIT)
		initStream(packet);

	if (_state == MP3_STATE_EOS)
		return;

	do {
		// If necessary, load more data into the stream decoder
		if (_stream.error == MAD_ERROR_BUFLEN)
			readMP3Data(packet);

		while (_state == MP3_STATE_READY) {
			_stream.error = MAD_ERROR_NONE;

			// Decode the next frame
			if (mad_frame_decode(&_frame, &_stream) == -1) {
				if (_stream.error == MAD_ERROR_BUFLEN) {
					break; // Read more data
				} else if (MAD_RECOVERABLE(_stream.error)) {
					// Note: we will occasionally see MAD_ERROR_BADDATAPTR errors here.
					// These are normal and expected (caused by our frame skipping (i.e. "seeking")
					// code above).
					debug(6, "MPEGAudioTrack::decodeMP3Data(): Recoverable error in mad_frame_decode (%s)", mad_stream_errorstr(&_stream));
					continue;
				} else {
					warning("MPEGAudioTrack::decodeMP3Data(): Unrecoverable error in mad_frame_decode (%s)", mad_stream_errorstr(&_stream));
					break;
				}
			}

			// Synthesize PCM data
			mad_synth_frame(&_synth, &_frame);

			// Output it to our queue
			if (_synth.pcm.length != 0) {
				byte *buffer = (byte *)malloc(_synth.pcm.length * 2 * MAD_NCHANNELS(&_frame.header));
				int16 *ptr = (int16 *)buffer;

				for (int i = 0; i < _synth.pcm.length; i++) {
					*ptr++ = (int16)scaleSample(_synth.pcm.samples[0][i]);

					if (MAD_NCHANNELS(&_frame.header) == 2)
						*ptr++ = (int16)scaleSample(_synth.pcm.samples[1][i]);
				}

				int flags = Audio::FLAG_16BITS;

				if (_audStream->isStereo())
					flags |= Audio::FLAG_STEREO;

#ifdef SCUMM_LITTLE_ENDIAN
				flags |= Audio::FLAG_LITTLE_ENDIAN;
#endif

				_audStream->queueBuffer(buffer, _synth.pcm.length * 2 * MAD_NCHANNELS(&_frame.header), DisposeAfterUse::YES, flags);
			}
			break;
		}
	} while (_state != MP3_STATE_EOS && _stream.error == MAD_ERROR_BUFLEN);

	if (_stream.error != MAD_ERROR_NONE)
		_state = MP3_STATE_EOS;
}

#endif

MPEGPSDecoder::PS2AudioTrack::PS2AudioTrack(Common::SeekableReadStream *firstPacket) {
	firstPacket->seek(12); // unknown data (4), 'SShd', header size (4)

	_soundType = firstPacket->readUint32LE();

	if (_soundType == PS2_ADPCM)
		error("Unhandled PS2 ADPCM sound in MPEG-PS video");
	else if (_soundType != PS2_PCM)
		error("Unknown PS2 sound type %x", _soundType);

	uint32 sampleRate = firstPacket->readUint32LE();
	_channels = firstPacket->readUint32LE();
	_interleave = firstPacket->readUint32LE();

	_blockBuffer = new byte[_interleave * _channels];
	_blockPos = _blockUsed = 0;
	_audStream = Audio::makeQueuingAudioStream(sampleRate, _channels == 2);
	_isFirstPacket = true;

	firstPacket->seek(0);
}

MPEGPSDecoder::PS2AudioTrack::~PS2AudioTrack() {
	delete[] _blockBuffer;
	delete _audStream;
}

bool MPEGPSDecoder::PS2AudioTrack::sendPacket(Common::SeekableReadStream *packet, uint32 pts, uint32 dts) {
	packet->skip(4);

	if (_isFirstPacket) {
		// Skip over the header which we already parsed
		packet->skip(4);
		packet->skip(packet->readUint32LE());

		if (packet->readUint32BE() != MKTAG('S', 'S', 'b', 'd'))
			error("Failed to find 'SSbd' tag");

		packet->readUint32LE(); // body size
		_isFirstPacket = false;
	}

	uint32 size = packet->size() - packet->pos();
	uint32 bytesPerChunk = _interleave * _channels;
	uint32 sampleCount = calculateSampleCount(size);

	byte *buffer = (byte *)malloc(sampleCount * 2);
	int16 *ptr = (int16 *)buffer;

	// Handle any full chunks first
	while (size >= bytesPerChunk) {
		packet->read(_blockBuffer + _blockPos, bytesPerChunk - _blockPos);
		size -= bytesPerChunk - _blockPos;
		_blockPos = 0;

		for (uint32 i = _blockUsed; i < _interleave / 2; i++)
			for (uint32 j = 0; j < _channels; j++)
				*ptr++ = READ_UINT16(_blockBuffer + i * 2 + j * _interleave);

		_blockUsed = 0;
	}

	// Then fallback on loading any leftover
	if (size > 0) {
		packet->read(_blockBuffer, size);
		_blockPos = size;

		if (size > (_channels - 1) * _interleave) {
			_blockUsed = (size - (_channels - 1) * _interleave) / 2;

			for (uint32 i = 0; i < _blockUsed; i++)
				for (uint32 j = 0; j < _channels; j++)
					*ptr++ = READ_UINT16(_blockBuffer + i * 2 + j * _interleave);
		}
	}

	byte flags = Audio::FLAG_16BITS | Audio::FLAG_LITTLE_ENDIAN;

	if (_audStream->isStereo())
		flags |= Audio::FLAG_STEREO;

	_audStream->queueBuffer((byte *)buffer, sampleCount * 2, DisposeAfterUse::YES, flags);

	delete packet;
	return true;
}

Audio::AudioStream *MPEGPSDecoder::PS2AudioTrack::getAudioStream() const {
	return _audStream;
}

uint32 MPEGPSDecoder::PS2AudioTrack::calculateSampleCount(uint32 packetSize) const {
	uint32 bytesPerChunk = _interleave * _channels, result = 0;

	// If we have a partial block, subtract the remainder from the size. That
    // gets put towards reading the partial block
	if (_blockPos != 0) {
		packetSize -= bytesPerChunk - _blockPos;
		result += (_interleave / 2) - _blockUsed;
	}

	// Round the number of whole chunks down and then calculate how many samples that gives us
	result += (packetSize / bytesPerChunk) * _interleave / 2;

	// Total up anything we can get from the remainder
	packetSize %= bytesPerChunk;
	if (packetSize > (_channels - 1) * _interleave)
		result += (packetSize - (_channels - 1) * _interleave) / 2;

	return result * _channels;
}

} // End of namespace Video