again fix logic around deciphering frame/sample number from frame header

src/libFLAC/stream_decoder.c

@@ -121,6 +121,7 @@ typedef struct FLAC__StreamDecoderPrivate {
 	FLAC__EntropyCodingMethod_PartitionedRiceContents partitioned_rice_contents[FLAC__MAX_CHANNELS];
 	unsigned output_capacity, output_channels;
 	FLAC__uint32 last_frame_number;
+	FLAC__uint32 last_block_size;
 	FLAC__uint64 samples_decoded;
 	FLAC__bool has_stream_info, has_seek_table;
 	FLAC__StreamMetadata stream_info;
@@ -284,6 +285,7 @@ FLAC_API FLAC__StreamDecoderState FLAC__stream_decoder_init(FLAC__StreamDecoder
 		return decoder->protected_->state = FLAC__STREAM_DECODER_MEMORY_ALLOCATION_ERROR;
 
 	decoder->private_->last_frame_number = 0;
+	decoder->private_->last_block_size = 0;
 	decoder->private_->samples_decoded = 0;
 	decoder->private_->has_stream_info = false;
 	decoder->private_->cached = false;
@@ -590,6 +592,8 @@ FLAC_API FLAC__bool FLAC__stream_decoder_flush(FLAC__StreamDecoder *decoder)
 		decoder->protected_->state = FLAC__STREAM_DECODER_MEMORY_ALLOCATION_ERROR;
 		return false;
 	}
+	decoder->private_->last_frame_number = 0;
+	decoder->private_->last_block_size = 0;
 	decoder->protected_->state = FLAC__STREAM_DECODER_SEARCH_FOR_FRAME_SYNC;
 
 	return true;
@@ -1702,18 +1706,34 @@ FLAC__bool read_frame_header_(FLAC__StreamDecoder *decoder)
 		return true;
 	}
 
-	if(blocksize_hint && is_known_variable_blocksize_stream) {
-		if(!FLAC__bitbuffer_read_utf8_uint64(decoder->private_->input, &xx, read_callback_, decoder, raw_header, &raw_header_len))
-			return false; /* the read_callback_ sets the state for us */
-		if(xx == FLAC__U64L(0xffffffffffffffff)) { /* i.e. non-UTF8 code... */
-			decoder->private_->lookahead = raw_header[raw_header_len-1]; /* back up as much as we can */
-			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;
+	/*
+	 * Now we get to the regrettable consequences of not knowing for sure
+	 * whether we got a frame number or a sample number.  There are no
+	 * encoders that do variable-blocksize encoding so unless we know from
+	 * the STREAMINFO that it is variable-blocksize we will assume it is
+	 * fixed-blocksize.  The trouble comes when we have no STREAMINFO; again
+	 * we will guess that is fixed-blocksize.  Where this can go wrong: 1) a
+	 * variable-blocksize stream with no STREAMINFO; 2) a fixed-blocksize
+	 * stream that was edited such that one or more frames before or
+	 * including this one do not have the same number of samples as the
+	 * STREAMINFO's min and max blocksize.
+	 */
+	if(is_known_variable_blocksize_stream) {
+		if(blocksize_hint) {
+			if(!FLAC__bitbuffer_read_utf8_uint64(decoder->private_->input, &xx, read_callback_, decoder, raw_header, &raw_header_len))
+				return false; /* the read_callback_ sets the state for us */
+			if(xx == FLAC__U64L(0xffffffffffffffff)) { /* i.e. non-UTF8 code... */
+				decoder->private_->lookahead = raw_header[raw_header_len-1]; /* back up as much as we can */
+				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;
+			}
+			decoder->private_->frame.header.number_type = FLAC__FRAME_NUMBER_TYPE_SAMPLE_NUMBER;
+			decoder->private_->frame.header.number.sample_number = xx;
 		}
-		decoder->private_->frame.header.number_type = FLAC__FRAME_NUMBER_TYPE_SAMPLE_NUMBER;
-		decoder->private_->frame.header.number.sample_number = xx;
+		else
+			is_unparseable = true;
 	}
 	else {
 		if(!FLAC__bitbuffer_read_utf8_uint32(decoder->private_->input, &x, read_callback_, decoder, raw_header, &raw_header_len))
@@ -1727,14 +1747,21 @@ FLAC__bool read_frame_header_(FLAC__StreamDecoder *decoder)
 		}
 		decoder->private_->last_frame_number = x;
 		decoder->private_->frame.header.number_type = FLAC__FRAME_NUMBER_TYPE_SAMPLE_NUMBER;
-		if(blocksize_hint) {
-			if(decoder->private_->has_stream_info)
-				decoder->private_->frame.header.number.sample_number = (FLAC__int64)decoder->private_->stream_info.data.stream_info.min_blocksize * (FLAC__int64)x;
+		if(decoder->private_->has_stream_info) {
+			FLAC__ASSERT(decoder->private_->stream_info.data.stream_info.min_blocksize == decoder->private_->stream_info.data.stream_info.max_blocksize);
+			decoder->private_->frame.header.number.sample_number = (FLAC__uint64)decoder->private_->stream_info.data.stream_info.min_blocksize * (FLAC__uint64)x;
+			decoder->private_->last_block_size = (FLAC__uint64)decoder->private_->frame.header.blocksize;
+		}
+		else if(blocksize_hint) {
+			if(decoder->private_->last_block_size)
+				decoder->private_->frame.header.number.sample_number = (FLAC__uint64)decoder->private_->last_block_size * (FLAC__uint64)x;
 			else
 				is_unparseable = true;
 		}
-		else	
-			decoder->private_->frame.header.number.sample_number = (FLAC__int64)decoder->private_->frame.header.blocksize * (FLAC__int64)x;
+		else {
+			decoder->private_->frame.header.number.sample_number = (FLAC__uint64)decoder->private_->frame.header.blocksize * (FLAC__uint64)x;
+			decoder->private_->last_block_size = (FLAC__uint64)decoder->private_->frame.header.blocksize;
+		}
 	}
 
 	if(blocksize_hint) {