stream_decoder.c

wince下著名的视频播放器源码

FLAC__bool frame_sync_(FLAC__StreamDecoder *decoder)
{
	FLAC__uint32 x;
	FLAC__bool first = true;

	/* If we know the total number of samples in the stream, stop if we've read that many. */
	/* This will stop us, for example, from wasting time trying to sync on an ID3V1 tag. */
	if(decoder->private_->has_stream_info && decoder->private_->stream_info.data.stream_info.total_samples) {
		if(decoder->private_->samples_decoded >= decoder->private_->stream_info.data.stream_info.total_samples) {
			decoder->protected_->state = FLAC__STREAM_DECODER_END_OF_STREAM;
			return true;
		}
	}

	/* make sure we're byte aligned */
	if(!FLAC__bitbuffer_is_consumed_byte_aligned(decoder->private_->input)) {
		if(!FLAC__bitbuffer_read_raw_uint32(decoder->private_->input, &x, FLAC__bitbuffer_bits_left_for_byte_alignment(decoder->private_->input), read_callback_, decoder))
			return false; /* the read_callback_ sets the state for us */
	}

	while(1) {
		if(decoder->private_->cached) {
			x = (FLAC__uint32)decoder->private_->lookahead;
			decoder->private_->cached = false;
		}
		else {
			if(!FLAC__bitbuffer_read_raw_uint32(decoder->private_->input, &x, 8, read_callback_, decoder))
				return false; /* the read_callback_ sets the state for us */
		}
		if(x == 0xff) { /* MAGIC NUMBER for the first 8 frame sync bits */
			decoder->private_->header_warmup[0] = (FLAC__byte)x;
			if(!FLAC__bitbuffer_read_raw_uint32(decoder->private_->input, &x, 8, read_callback_, decoder))
				return false; /* the read_callback_ sets the state for us */

			/* we have to check if we just read two 0xff's in a row; the second may actually be the beginning of the sync code */
			/* else we have to check if the second byte is the end of a sync code */
			if(x == 0xff) { /* MAGIC NUMBER for the first 8 frame sync bits */
				decoder->private_->lookahead = (FLAC__byte)x;
				decoder->private_->cached = true;
			}
			else if(x >> 2 == 0x3e) { /* MAGIC NUMBER for the last 6 sync bits */
				decoder->private_->header_warmup[1] = (FLAC__byte)x;
				decoder->protected_->state = FLAC__STREAM_DECODER_READ_FRAME;
				return true;
			}
		}
		if(first) {
			decoder->private_->error_callback(decoder, FLAC__STREAM_DECODER_ERROR_STATUS_LOST_SYNC, decoder->private_->client_data);
			first = false;
		}
	}

	return true;
}

FLAC__bool read_frame_(FLAC__StreamDecoder *decoder, FLAC__bool *got_a_frame, FLAC__bool do_full_decode)
{
	unsigned channel;
	unsigned i;
	FLAC__int32 mid, side, left, right;
	FLAC__uint16 frame_crc; /* the one we calculate from the input stream */
	FLAC__uint32 x;

	*got_a_frame = false;

	/* init the CRC */
	frame_crc = 0;
	FLAC__CRC16_UPDATE(decoder->private_->header_warmup[0], frame_crc);
	FLAC__CRC16_UPDATE(decoder->private_->header_warmup[1], frame_crc);
	FLAC__bitbuffer_reset_read_crc16(decoder->private_->input, frame_crc);

	if(!read_frame_header_(decoder))
		return false;
	if(decoder->protected_->state == FLAC__STREAM_DECODER_SEARCH_FOR_FRAME_SYNC)
		return true;
	if(!allocate_output_(decoder, decoder->private_->frame.header.blocksize, decoder->private_->frame.header.channels))
		return false;
	for(channel = 0; channel < decoder->private_->frame.header.channels; channel++) {
		/*
		 * first figure the correct bits-per-sample of the subframe
		 */
		unsigned bps = decoder->private_->frame.header.bits_per_sample;
		switch(decoder->private_->frame.header.channel_assignment) {
			case FLAC__CHANNEL_ASSIGNMENT_INDEPENDENT:
				/* no adjustment needed */
				break;
			case FLAC__CHANNEL_ASSIGNMENT_LEFT_SIDE:
				FLAC__ASSERT(decoder->private_->frame.header.channels == 2);
				if(channel == 1)
					bps++;
				break;
			case FLAC__CHANNEL_ASSIGNMENT_RIGHT_SIDE:
				FLAC__ASSERT(decoder->private_->frame.header.channels == 2);
				if(channel == 0)
					bps++;
				break;
			case FLAC__CHANNEL_ASSIGNMENT_MID_SIDE:
				FLAC__ASSERT(decoder->private_->frame.header.channels == 2);
				if(channel == 1)
					bps++;
				break;
			default:
				FLAC__ASSERT(0);
		}
		/*
		 * now read it
		 */
		if(!read_subframe_(decoder, channel, bps, do_full_decode))
			return false;
		if(decoder->protected_->state != FLAC__STREAM_DECODER_READ_FRAME) {
			decoder->protected_->state = FLAC__STREAM_DECODER_SEARCH_FOR_FRAME_SYNC;
			return true;
		}
	}
	if(!read_zero_padding_(decoder))
		return false;

	/*
	 * Read the frame CRC-16 from the footer and check
	 */
	frame_crc = FLAC__bitbuffer_get_read_crc16(decoder->private_->input);
	if(!FLAC__bitbuffer_read_raw_uint32(decoder->private_->input, &x, FLAC__FRAME_FOOTER_CRC_LEN, read_callback_, decoder))
		return false; /* the read_callback_ sets the state for us */
	if(frame_crc == (FLAC__uint16)x) {
		if(do_full_decode) {
			/* Undo any special channel coding */
			switch(decoder->private_->frame.header.channel_assignment) {
				case FLAC__CHANNEL_ASSIGNMENT_INDEPENDENT:
					/* do nothing */
					break;
				case FLAC__CHANNEL_ASSIGNMENT_LEFT_SIDE:
					FLAC__ASSERT(decoder->private_->frame.header.channels == 2);
					for(i = 0; i < decoder->private_->frame.header.blocksize; i++)
						decoder->private_->output[1][i] = decoder->private_->output[0][i] - decoder->private_->output[1][i];
					break;
				case FLAC__CHANNEL_ASSIGNMENT_RIGHT_SIDE:
					FLAC__ASSERT(decoder->private_->frame.header.channels == 2);
					for(i = 0; i < decoder->private_->frame.header.blocksize; i++)
						decoder->private_->output[0][i] += decoder->private_->output[1][i];
					break;
				case FLAC__CHANNEL_ASSIGNMENT_MID_SIDE:
					FLAC__ASSERT(decoder->private_->frame.header.channels == 2);
					for(i = 0; i < decoder->private_->frame.header.blocksize; i++) {
						mid = decoder->private_->output[0][i];
						side = decoder->private_->output[1][i];
						mid <<= 1;
						if(side & 1) /* i.e. if 'side' is odd... */
							mid++;
						left = mid + side;
						right = mid - side;
						decoder->private_->output[0][i] = left >> 1;
						decoder->private_->output[1][i] = right >> 1;
					}
					break;
				default:
					FLAC__ASSERT(0);
					break;
			}
		}
	}
	else {
		/* Bad frame, emit error and zero the output signal */
		decoder->private_->error_callback(decoder, FLAC__STREAM_DECODER_ERROR_STATUS_FRAME_CRC_MISMATCH, decoder->private_->client_data);
		if(do_full_decode) {
			for(channel = 0; channel < decoder->private_->frame.header.channels; channel++) {
				memset(decoder->private_->output[channel], 0, sizeof(FLAC__int32) * decoder->private_->frame.header.blocksize);
			}
		}
	}

	*got_a_frame = true;

	/* put the latest values into the public section of the decoder instance */
	decoder->protected_->channels = decoder->private_->frame.header.channels;
	decoder->protected_->channel_assignment = decoder->private_->frame.header.channel_assignment;
	decoder->protected_->bits_per_sample = decoder->private_->frame.header.bits_per_sample;
	decoder->protected_->sample_rate = decoder->private_->frame.header.sample_rate;
	decoder->protected_->blocksize = decoder->private_->frame.header.blocksize;

	FLAC__ASSERT(decoder->private_->frame.header.number_type == FLAC__FRAME_NUMBER_TYPE_SAMPLE_NUMBER);
	decoder->private_->samples_decoded = decoder->private_->frame.header.number.sample_number + decoder->private_->frame.header.blocksize;

	/* write it */
	if(do_full_decode) {
		if(decoder->private_->write_callback(decoder, &decoder->private_->frame, (const FLAC__int32 * const *)decoder->private_->output, decoder->private_->client_data) != FLAC__STREAM_DECODER_WRITE_STATUS_CONTINUE)
			return false;
	}

	decoder->protected_->state = FLAC__STREAM_DECODER_SEARCH_FOR_FRAME_SYNC;
	return true;
}

FLAC__bool read_frame_header_(FLAC__StreamDecoder *decoder)
{
	FLAC__uint32 x;
	FLAC__uint64 xx;
	unsigned i, blocksize_hint = 0, sample_rate_hint = 0;
	FLAC__byte crc8, raw_header[16]; /* MAGIC NUMBER based on the maximum frame header size, including CRC */
	unsigned raw_header_len;
	FLAC__bool is_unparseable = false;
	const FLAC__bool is_known_variable_blocksize_stream = (decoder->private_->has_stream_info && decoder->private_->stream_info.data.stream_info.min_blocksize != decoder->private_->stream_info.data.stream_info.max_blocksize);
	const FLAC__bool is_known_fixed_blocksize_stream = (decoder->private_->has_stream_info && decoder->private_->stream_info.data.stream_info.min_blocksize == decoder->private_->stream_info.data.stream_info.max_blocksize);

	FLAC__ASSERT(FLAC__bitbuffer_is_consumed_byte_aligned(decoder->private_->input));

	/* init the raw header with the saved bits from synchronization */
	raw_header[0] = decoder->private_->header_warmup[0];
	raw_header[1] = decoder->private_->header_warmup[1];
	raw_header_len = 2;

	/*
	 * check to make sure that the reserved bits are 0
	 */
	if(raw_header[1] & 0x03) { /* MAGIC NUMBER */
		is_unparseable = true;
	}

	/*
	 * Note that along the way as we read the header, we look for a sync
	 * code inside.  If we find one it would indicate that our original
	 * sync was bad since there cannot be a sync code in a valid header.
	 */

	/*
	 * read in the raw header as bytes so we can CRC it, and parse it on the way
	 */
	for(i = 0; i < 2; i++) {
		if(!FLAC__bitbuffer_read_raw_uint32(decoder->private_->input, &x, 8, read_callback_, decoder))
			return false; /* the read_callback_ sets the state for us */
		if(x == 0xff) { /* MAGIC NUMBER for the first 8 frame sync bits */
			/* if we get here it means our original sync was erroneous since the sync code cannot appear in the header */
			decoder->private_->lookahead = (FLAC__byte)x;
			decoder->private_->cached = true;
			decoder->private_->error_callback(decoder, FLAC__STREAM_DECODER_ERROR_STATUS_BAD_HEADER, decoder->private_->client_data);
			decoder->protected_->state = FLAC__STREAM_DECODER_SEARCH_FOR_FRAME_SYNC;
			return true;
		}
		raw_header[raw_header_len++] = (FLAC__byte)x;
	}

	switch(x = raw_header[2] >> 4) {
		case 0:
			if(is_known_fixed_blocksize_stream)
				decoder->private_->frame.header.blocksize = decoder->private_->stream_info.data.stream_info.min_blocksize;
			else
				is_unparseable = true;
			break;
		case 1:
			decoder->private_->frame.header.blocksize = 192;
			break;
		case 2:
		case 3:
		case 4:
		case 5:
			decoder->private_->frame.header.blocksize = 576 << (x-2);
			break;
		case 6:
		case 7:
			blocksize_hint = x;
			break;
		case 8:
		case 9:
		case 10:
		case 11:
		case 12:
		case 13:
		case 14:
		case 15:
			decoder->private_->frame.header.blocksize = 256 << (x-8);
			break;
		default:
			FLAC__ASSERT(0);
			break;
	}

	switch(x = raw_header[2] & 0x0f) {
		case 0:
			if(decoder->private_->has_stream_info)
				decoder->private_->frame.header.sample_rate = decoder->private_->stream_info.data.stream_info.sample_rate;
			else
				is_unparseable = true;
			break;
		case 1:
		case 2:
		case 3:
			is_unparseable = true;
			break;
		case 4:
			decoder->private_->frame.header.sample_rate = 8000;
			break;
		case 5:
			decoder->private_->frame.header.sample_rate = 16000;
			break;
		case 6:
			decoder->private_->frame.header.sample_rate = 22050;
			break;
		case 7:
			decoder->private_->frame.header.sample_rate = 24000;
			break;
		case 8:
			decoder->private_->frame.header.sample_rate = 32000;
			break;
		case 9:
			decoder->private_->frame.header.sample_rate = 44100;
			break;
		case 10:
			decoder->private_->frame.header.sample_rate = 48000;
			break;
		case 11:
			decoder->private_->frame.header.sample_rate = 96000;
			break;
		case 12:
		case 13:
		case 14:
			sample_rate_hint = x;
			break;
		case 15:
			decoder->private_->error_callback(decoder, FLAC__STREAM_DECODER_ERROR_STATUS_BAD_HEADER, decoder->private_->client_data);
			decoder->protected_->state = FLAC__STREAM_DECODER_SEARCH_FOR_FRAME_SYNC;
			return true;
		default:
			FLAC__ASSERT(0);
	}

	x = (unsigned)(raw_header[3] >> 4);
	if(x & 8) {
		decoder->private_->frame.heade