1 /* libFLAC - Free Lossless Audio Codec library
2 * Copyright (C) 2000,2001,2002 Josh Coalson
4 * This library is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU Library General Public
6 * License as published by the Free Software Foundation; either
7 * version 2 of the License, or (at your option) any later version.
9 * This library is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * Library General Public License for more details.
14 * You should have received a copy of the GNU Library General Public
15 * License along with this library; if not, write to the
16 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
17 * Boston, MA 02111-1307, USA.
20 #ifndef FLAC__FORMAT_H
21 #define FLAC__FORMAT_H
29 /** \file include/FLAC/format.h
32 * This module contains structure definitions for the representation
33 * of FLAC format components in memory. These are the basic
34 * structures used by the rest of the interfaces.
36 * See the detailed documentation in the
37 * \link flac_format format \endlink module.
40 /** \defgroup flac_format FLAC/format.h: format components
44 * This module contains structure definitions for the representation
45 * of FLAC format components in memory. These are the basic
46 * structures used by the rest of the interfaces.
48 * First, you should be familiar with the
49 * <A HREF="../format.html">FLAC format</A>. Many of the values here
50 * follow directly from the specification. As a user of libFLAC, the
51 * interesting parts really are the structures that describe the frame
52 * header and metadata blocks.
54 * The format structures here are very primitive, designed to store
55 * information in an efficient way. Reading information from the
56 * structures is easy but creating or modifying them directly is
57 * more complex. For the most part, as a user of a library, editing
58 * is not necessary; however, for metadata blocks it is, so there are
59 * convenience functions provided in the metadata module to simplify
60 * the manipulation of metadata blocks.
63 * It's not the best convention, but symbols ending in _LEN are in bits
64 * and _LENGTH are in bytes. _LENGTH symbols are \#defines instead of
65 * global variables because they are usually used when declaring byte
66 * arrays and some compilers require compile-time knowledge of array
67 * sizes when declared on the stack.
74 Most of the values described in this file are defined by the FLAC
75 format specification. There is nothing to tune here.
78 /** The minimum block size, in samples, permitted by the format. */
79 #define FLAC__MIN_BLOCK_SIZE (16u)
81 /** The maximum block size, in samples, permitted by the format. */
82 #define FLAC__MAX_BLOCK_SIZE (65535u)
84 /** The maximum number of channels permitted by the format. */
85 #define FLAC__MAX_CHANNELS (8u)
87 /** The minimum sample resolution permitted by the format. */
88 #define FLAC__MIN_BITS_PER_SAMPLE (4u)
90 /** The maximum sample resolution permitted by the format. */
91 #define FLAC__MAX_BITS_PER_SAMPLE (32u)
93 /** The maximum sample resolution permitted by libFLAC.
96 * FLAC__MAX_BITS_PER_SAMPLE is the limit of the FLAC format. However,
97 * the reference encoder/decoder is currently limited to 24 bits because
98 * of prevalent 32-bit math, so make sure and use this value when
101 #define FLAC__REFERENCE_CODEC_MAX_BITS_PER_SAMPLE (24u)
103 /** The maximum sample rate permitted by the format. The value is
104 * ((2 ^ 16) - 1) * 10; see <A HREF="../format.html">FLAC format</A>
107 #define FLAC__MAX_SAMPLE_RATE (655350u)
109 /** The maximum LPC order permitted by the format. */
110 #define FLAC__MAX_LPC_ORDER (32u)
112 /** The minimum quantized linear predictor coefficient precision
113 * permitted by the format.
115 #define FLAC__MIN_QLP_COEFF_PRECISION (5u)
117 /** The maximum order of the fixed predictors permitted by the format. */
118 #define FLAC__MAX_FIXED_ORDER (4u)
120 /** The maximum Rice partition order permitted by the format. */
121 #define FLAC__MAX_RICE_PARTITION_ORDER (15u)
123 /* VERSION should come from configure */
125 /** The version string of the current library.
128 * This does not correspond to the shared library version number, which
129 * is used to determine binary compatibility.
131 #define FLAC__VERSION_STRING VERSION
134 /** The byte string representation of the beginning of a FLAC stream. */
135 extern const FLAC__byte FLAC__STREAM_SYNC_STRING[4]; /* = "fLaC" */;
137 /** The 32-bit integer big-endian representation of the beginning of
140 extern const unsigned FLAC__STREAM_SYNC; /* = 0x664C6143 */;
142 /** The length of the FLAC signature in bits. */
143 extern const unsigned FLAC__STREAM_SYNC_LEN; /* = 32 bits */;
145 /** The length of the FLAC signature in bytes. */
146 #define FLAC__STREAM_SYNC_LENGTH (4u)
149 /*****************************************************************************
151 * NOTE: Within the bitstream, all fixed-width numbers are big-endian coded.
152 * All numbers are unsigned unless otherwise noted.
154 *****************************************************************************/
157 /*****************************************************************************
159 * Subframe structures
161 *****************************************************************************/
163 /*****************************************************************************/
165 /** An enumeration of the available entropy coding methods. */
167 FLAC__ENTROPY_CODING_METHOD_PARTITIONED_RICE = 0
168 /**< Residual is coded by partitioning into contexts, each with it's own
170 } FLAC__EntropyCodingMethodType;
172 /** Maps a FLAC__EntropyCodingMethodType to a C string.
174 * Using a FLAC__EntropyCodingMethodType as the index to this array will
175 * give the string equivalent. The contents should not be modified.
177 extern const char * const FLAC__EntropyCodingMethodTypeString[];
180 /** Header for a Rice partition. (c.f. <A HREF="../format.html#partitioned_rice">format specification</A>)
185 /**< The partition order, i.e. # of contexts = 2 ^ \a order. */
187 unsigned *parameters;
188 /**< The Rice parameters for each context. */
191 /**< Widths for escape-coded partitions. */
193 unsigned capacity_by_order;
194 /**< The capacity of the \a parameters and \a raw_bits arrays
195 * specified as an order, i.e. the number of array elements
196 * allocated is 2 ^ \a capacity_by_order.
198 } FLAC__EntropyCodingMethod_PartitionedRice;
200 extern const unsigned FLAC__ENTROPY_CODING_METHOD_PARTITIONED_RICE_ORDER_LEN; /**< == 4 (bits) */
201 extern const unsigned FLAC__ENTROPY_CODING_METHOD_PARTITIONED_RICE_PARAMETER_LEN; /**< == 4 (bits) */
202 extern const unsigned FLAC__ENTROPY_CODING_METHOD_PARTITIONED_RICE_RAW_LEN; /**< == 5 (bits) */
204 extern const unsigned FLAC__ENTROPY_CODING_METHOD_PARTITIONED_RICE_ESCAPE_PARAMETER;
205 /**< == (1<<FLAC__ENTROPY_CODING_METHOD_PARTITIONED_RICE_PARAMETER_LEN)-1 */
207 /** Header for the entropy coding method. (c.f. <A HREF="../format.html#residual">format specification</A>)
210 FLAC__EntropyCodingMethodType type;
212 FLAC__EntropyCodingMethod_PartitionedRice partitioned_rice;
214 } FLAC__EntropyCodingMethod;
216 extern const unsigned FLAC__ENTROPY_CODING_METHOD_TYPE_LEN; /**< == 2 (bits) */
218 /*****************************************************************************/
220 /** An enumeration of the available subframe types. */
222 FLAC__SUBFRAME_TYPE_CONSTANT = 0, /**< constant signal */
223 FLAC__SUBFRAME_TYPE_VERBATIM = 1, /**< uncompressed signal */
224 FLAC__SUBFRAME_TYPE_FIXED = 2, /**< fixed polynomial prediction */
225 FLAC__SUBFRAME_TYPE_LPC = 3 /**< linear prediction */
226 } FLAC__SubframeType;
228 /** Maps a FLAC__SubframeType to a C string.
230 * Using a FLAC__SubframeType as the index to this array will
231 * give the string equivalent. The contents should not be modified.
233 extern const char * const FLAC__SubframeTypeString[];
236 /** CONSTANT subframe. (c.f. <A HREF="../format.html#subframe_constant">format specification</A>)
239 FLAC__int32 value; /**< The constant signal value. */
240 } FLAC__Subframe_Constant;
243 /** VERBATIM subframe. (c.f. <A HREF="../format.html#subframe_verbatim">format specification</A>)
246 const FLAC__int32 *data; /**< A pointer to verbatim signal. */
247 } FLAC__Subframe_Verbatim;
250 /** FIXED subframe. (c.f. <A HREF="../format.html#subframe_fixed">format specification</A>)
253 FLAC__EntropyCodingMethod entropy_coding_method;
254 /**< The residual coding method. */
257 /**< The polynomial order. */
259 FLAC__int32 warmup[FLAC__MAX_FIXED_ORDER];
260 /**< Warmup samples to prime the predictor, length == order. */
262 const FLAC__int32 *residual;
263 /**< The residual signal, length == (blocksize minus order) samples. */
264 } FLAC__Subframe_Fixed;
267 /** LPC subframe. (c.f. <A HREF="../format.html#subframe_lpc">format specification</A>)
270 FLAC__EntropyCodingMethod entropy_coding_method;
271 /**< The residual coding method. */
274 /**< The FIR order. */
276 unsigned qlp_coeff_precision;
277 /**< Quantized FIR filter coefficient precision in bits. */
279 int quantization_level;
280 /**< The qlp coeff shift needed. */
282 FLAC__int32 qlp_coeff[FLAC__MAX_LPC_ORDER];
283 /**< FIR filter coefficients. */
285 FLAC__int32 warmup[FLAC__MAX_LPC_ORDER];
286 /**< Warmup samples to prime the predictor, length == order. */
288 const FLAC__int32 *residual;
289 /**< The residual signal, length == (blocksize minus order) samples. */
290 } FLAC__Subframe_LPC;
292 extern const unsigned FLAC__SUBFRAME_LPC_QLP_COEFF_PRECISION_LEN; /**< == 4 (bits) */
293 extern const unsigned FLAC__SUBFRAME_LPC_QLP_SHIFT_LEN; /**< == 5 (bits) */
296 /** FLAC subframe structure. (c.f. <A HREF="../format.html#subframe">format specification</A>)
299 FLAC__SubframeType type;
301 FLAC__Subframe_Constant constant;
302 FLAC__Subframe_Fixed fixed;
303 FLAC__Subframe_LPC lpc;
304 FLAC__Subframe_Verbatim verbatim;
306 unsigned wasted_bits;
309 extern const unsigned FLAC__SUBFRAME_ZERO_PAD_LEN; /**< == 1 (bit) */
310 extern const unsigned FLAC__SUBFRAME_TYPE_LEN; /**< == 6 (bits) */
311 extern const unsigned FLAC__SUBFRAME_WASTED_BITS_FLAG_LEN; /**< == 1 (bit) */
313 extern const unsigned FLAC__SUBFRAME_TYPE_CONSTANT_BYTE_ALIGNED_MASK; /* = 0x00 */
314 extern const unsigned FLAC__SUBFRAME_TYPE_VERBATIM_BYTE_ALIGNED_MASK; /* = 0x02 */
315 extern const unsigned FLAC__SUBFRAME_TYPE_FIXED_BYTE_ALIGNED_MASK; /* = 0x10 */
316 extern const unsigned FLAC__SUBFRAME_TYPE_LPC_BYTE_ALIGNED_MASK; /* = 0x40 */
318 /*****************************************************************************/
321 /*****************************************************************************
325 *****************************************************************************/
327 /** An enumeration of the available channel assignments. */
329 FLAC__CHANNEL_ASSIGNMENT_INDEPENDENT = 0, /**< independent channels */
330 FLAC__CHANNEL_ASSIGNMENT_LEFT_SIDE = 1, /**< left+side stereo */
331 FLAC__CHANNEL_ASSIGNMENT_RIGHT_SIDE = 2, /**< right+side stereo */
332 FLAC__CHANNEL_ASSIGNMENT_MID_SIDE = 3 /**< mid+side stereo */
333 } FLAC__ChannelAssignment;
335 /** Maps a FLAC__ChannelAssignment to a C string.
337 * Using a FLAC__ChannelAssignment as the index to this array will
338 * give the string equivalent. The contents should not be modified.
340 extern const char * const FLAC__ChannelAssignmentString[];
342 /** An enumeration of the possible frame numbering methods. */
344 FLAC__FRAME_NUMBER_TYPE_FRAME_NUMBER, /**< number contains the frame number */
345 FLAC__FRAME_NUMBER_TYPE_SAMPLE_NUMBER /**< number contains the sample number of first sample in frame */
346 } FLAC__FrameNumberType;
348 /** Maps a FLAC__FrameNumberType to a C string.
350 * Using a FLAC__FrameNumberType as the index to this array will
351 * give the string equivalent. The contents should not be modified.
353 extern const char * const FLAC__FrameNumberTypeString[];
356 /** FLAC frame header structure. (c.f. <A HREF="../format.html#frame_header">format specification</A>)
360 /**< The number of samples per subframe. */
362 unsigned sample_rate;
363 /**< The sample rate in Hz. */
366 /**< The number of channels (== number of subframes). */
368 FLAC__ChannelAssignment channel_assignment;
369 /**< The channel assignment for the frame. */
371 unsigned bits_per_sample;
372 /**< The sample resolution. */
374 FLAC__FrameNumberType number_type;
375 /**< The numbering scheme used for the frame. */
378 FLAC__uint32 frame_number;
379 FLAC__uint64 sample_number;
381 /**< The frame number or sample number of first sample in frame;
382 * use the \a number_type value to determine which to use. */
385 /**< CRC-8 (polynomial = x^8 + x^2 + x^1 + x^0, initialized with 0)
386 * of the raw frame header bytes, meaning everything before the CRC byte
387 * including the sync code.
391 extern const unsigned FLAC__FRAME_HEADER_SYNC; /**< == 0x3ffe; the frame header sync code */
392 extern const unsigned FLAC__FRAME_HEADER_SYNC_LEN; /**< == 14 (bits) */
393 extern const unsigned FLAC__FRAME_HEADER_RESERVED_LEN; /**< == 2 (bits) */
394 extern const unsigned FLAC__FRAME_HEADER_BLOCK_SIZE_LEN; /**< == 4 (bits) */
395 extern const unsigned FLAC__FRAME_HEADER_SAMPLE_RATE_LEN; /**< == 4 (bits) */
396 extern const unsigned FLAC__FRAME_HEADER_CHANNEL_ASSIGNMENT_LEN; /**< == 4 (bits) */
397 extern const unsigned FLAC__FRAME_HEADER_BITS_PER_SAMPLE_LEN; /**< == 3 (bits) */
398 extern const unsigned FLAC__FRAME_HEADER_ZERO_PAD_LEN; /**< == 1 (bit) */
399 extern const unsigned FLAC__FRAME_HEADER_CRC_LEN; /**< == 8 (bits) */
402 /** FLAC frame footer structure. (c.f. <A HREF="../format.html#frame_footer">format specification</A>)
406 /**< CRC-16 (polynomial = x^16 + x^15 + x^2 + x^0, initialized with
407 * 0) of the bytes before the crc, back to and including the frame header
412 extern const unsigned FLAC__FRAME_FOOTER_CRC_LEN; /**< == 16 (bits) */
415 /** FLAC frame structure. (c.f. <A HREF="../format.html#frame">format specification</A>)
418 FLAC__FrameHeader header;
419 FLAC__Subframe subframes[FLAC__MAX_CHANNELS];
420 FLAC__FrameFooter footer;
423 /*****************************************************************************/
426 /*****************************************************************************
428 * Meta-data structures
430 *****************************************************************************/
432 /** An enumeration of the available metadata block types. */
435 FLAC__METADATA_TYPE_STREAMINFO = 0,
436 /**< <A HREF="../format.html#metadata_block_streaminfo">STREAMINFO</A> block */
438 FLAC__METADATA_TYPE_PADDING = 1,
439 /**< <A HREF="../format.html#metadata_block_padding"PADDING</A> block */
441 FLAC__METADATA_TYPE_APPLICATION = 2,
442 /**< <A HREF="../format.html#metadata_block_application"APPLICATION</A> block */
444 FLAC__METADATA_TYPE_SEEKTABLE = 3,
445 /**< <A HREF="../format.html#metadata_block_seektable"SEEKTABLE</A> block */
447 FLAC__METADATA_TYPE_VORBIS_COMMENT = 4,
448 /**< <A HREF="../format.html#metadata_block_vorbis_comment"VORBISCOMMENT</A> block */
450 } FLAC__MetadataType;
452 /** Maps a FLAC__MetadataType to a C string.
454 * Using a FLAC__MetadataType as the index to this array will
455 * give the string equivalent. The contents should not be modified.
457 extern const char * const FLAC__MetadataTypeString[];
460 /** FLAC STREAMINFO structure. (c.f. <A HREF="../format.html#metadata_block_streaminfo">format specification</A>)
463 unsigned min_blocksize, max_blocksize;
464 unsigned min_framesize, max_framesize;
465 unsigned sample_rate;
467 unsigned bits_per_sample;
468 FLAC__uint64 total_samples;
469 FLAC__byte md5sum[16];
470 } FLAC__StreamMetadata_StreamInfo;
472 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_MIN_BLOCK_SIZE_LEN; /**< == 16 (bits) */
473 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_MAX_BLOCK_SIZE_LEN; /**< == 16 (bits) */
474 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_MIN_FRAME_SIZE_LEN; /**< == 24 (bits) */
475 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_MAX_FRAME_SIZE_LEN; /**< == 24 (bits) */
476 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_SAMPLE_RATE_LEN; /**< == 20 (bits) */
477 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_CHANNELS_LEN; /**< == 3 (bits) */
478 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_BITS_PER_SAMPLE_LEN; /**< == 5 (bits) */
479 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_TOTAL_SAMPLES_LEN; /**< == 36 (bits) */
480 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_MD5SUM_LEN; /**< == 128 (bits) */
482 /** The total stream length of the STREAMINFO block in bytes. */
483 #define FLAC__STREAM_METADATA_STREAMINFO_LENGTH (34u)
485 /** FLAC PADDING structure. (c.f. <A HREF="../format.html#metadata_block_padding">format specification</A>)
489 /**< Conceptually this is an empty struct since we don't store the
490 * padding bytes. Empty structs are not allowed by some C compilers,
493 } FLAC__StreamMetadata_Padding;
496 /** FLAC APPLICATION structure. (c.f. <A HREF="../format.html#metadata_block_application">format specification</A>)
501 } FLAC__StreamMetadata_Application;
503 extern const unsigned FLAC__STREAM_METADATA_APPLICATION_ID_LEN; /**< == 32 (bits) */
505 /** SeekPoint structure used in SEEKTABLE blocks. (c.f. <A HREF="../format.html#seekpoint">format specification</A>)
508 FLAC__uint64 sample_number;
509 /**< The sample number of the target frame. */
511 FLAC__uint64 stream_offset;
512 /**< The offset, in bytes, of the target frame with respect to
513 * beginning of the first frame. */
515 unsigned frame_samples;
516 /**< The number of samples in the target frame. */
517 } FLAC__StreamMetadata_SeekPoint;
519 extern const unsigned FLAC__STREAM_METADATA_SEEKPOINT_SAMPLE_NUMBER_LEN; /**< == 64 (bits) */
520 extern const unsigned FLAC__STREAM_METADATA_SEEKPOINT_STREAM_OFFSET_LEN; /**< == 64 (bits) */
521 extern const unsigned FLAC__STREAM_METADATA_SEEKPOINT_FRAME_SAMPLES_LEN; /**< == 16 (bits) */
523 /** The total stream length of a seek point in bytes. */
524 #define FLAC__STREAM_METADATA_SEEKPOINT_LENGTH (18u)
526 /** The value used in the \a sample_number field of
527 * FLAC__StreamMetadataSeekPoint used to indicate a placeholder
528 * point (== 0xffffffffffffffff).
530 extern const FLAC__uint64 FLAC__STREAM_METADATA_SEEKPOINT_PLACEHOLDER;
533 /** FLAC SEEKTABLE structure. (c.f. <A HREF="../format.html#metadata_block_seektable">format specification</A>)
535 * \note From the format specification:
536 * - The seek points must be sorted by ascending sample number.
537 * - Each seek point's sample number must be the first sample of the
539 * - Each seek point's sample number must be unique within the table.
540 * - Existence of a SEEKTABLE block implies a correct setting of
541 * total_samples in the stream_info block.
542 * - Behavior is undefined when more than one SEEKTABLE block is
543 * present in a stream.
547 FLAC__StreamMetadata_SeekPoint *points;
548 } FLAC__StreamMetadata_SeekTable;
551 /** Vorbis comment entry structure used in VORBIS_COMMENT blocks. (c.f. <A HREF="../format.html#metadata_block_vorbis_comment">format specification</A>)
556 } FLAC__StreamMetadata_VorbisComment_Entry;
558 extern const unsigned FLAC__STREAM_METADATA_VORBIS_COMMENT_ENTRY_LENGTH_LEN; /**< == 32 (bits) */
561 /** FLAC VORBIS_COMMENT structure. (c.f. <A HREF="../format.html#metadata_block_vorbis_comment">format specification</A>)
564 FLAC__StreamMetadata_VorbisComment_Entry vendor_string;
565 FLAC__uint32 num_comments;
566 FLAC__StreamMetadata_VorbisComment_Entry *comments;
567 } FLAC__StreamMetadata_VorbisComment;
569 extern const unsigned FLAC__STREAM_METADATA_VORBIS_COMMENT_NUM_COMMENTS_LEN; /**< == 32 (bits) */
572 /** FLAC metadata block structure. (c.f. <A HREF="../format.html#metadata_block">format specification</A>)
575 FLAC__MetadataType type;
576 /**< The type of the metadata block; used determine which member of the
577 * \a data union to dereference. */
580 /**< \c true if this metadata block is the last, else \a false */
583 /**< Length, in bytes, of the block data as it appears in the stream. */
586 FLAC__StreamMetadata_StreamInfo stream_info;
587 FLAC__StreamMetadata_Padding padding;
588 FLAC__StreamMetadata_Application application;
589 FLAC__StreamMetadata_SeekTable seek_table;
590 FLAC__StreamMetadata_VorbisComment vorbis_comment;
592 /**< Polymorphic block data; use the \a type value to determine which
594 } FLAC__StreamMetadata;
596 extern const unsigned FLAC__STREAM_METADATA_IS_LAST_LEN; /**< == 1 (bit) */
597 extern const unsigned FLAC__STREAM_METADATA_TYPE_LEN; /**< == 7 (bits) */
598 extern const unsigned FLAC__STREAM_METADATA_LENGTH_LEN; /**< == 24 (bits) */
600 /** The total stream length of a metadata block header in bytes. */
601 #define FLAC__STREAM_METADATA_HEADER_LENGTH (4u)
603 /*****************************************************************************/
606 /*****************************************************************************
610 *****************************************************************************/
612 /** Tests that a sample rate is valid for FLAC. Since the rules for valid
613 * sample rates are slightly complex, they are encapsulated in this function.
615 * \param sample_rate The sample rate to test for compliance.
617 * \c true if the given sample rate conforms to the specification, else
620 FLAC__bool FLAC__format_sample_rate_is_valid(unsigned sample_rate);
622 /** Check a seek table to see if it conforms to the FLAC specification.
623 * See the format specification for limits on the contents of the
626 * \param seek_table A pointer to a seek table to be checked.
628 * \code seek_table != NULL \endcode
630 * \c false if seek table is illegal, else \c true.
632 FLAC__bool FLAC__format_seektable_is_legal(const FLAC__StreamMetadata_SeekTable *seek_table);
634 /** Sort a seek table's seek points according to the format specification.
635 * This includes a "unique-ification" step to remove duplicates, i.e.
636 * seek points with identical \a sample_number values. Duplicate seek
637 * points are converted into placeholder points and sorted to the end of
640 * \param seek_table A pointer to a seek table to be sorted.
642 * \code seek_table != NULL \endcode
644 * The number of duplicate seek points converted into placeholders.
646 unsigned FLAC__format_seektable_sort(FLAC__StreamMetadata_SeekTable *seek_table);