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 ^ order. */
187 unsigned parameters[1 << FLAC__MAX_RICE_PARTITION_ORDER];
188 /**< The Rice parameters for each context. */
190 unsigned raw_bits[1 << FLAC__MAX_RICE_PARTITION_ORDER];
191 /**< Widths for escape-coded partitions. */
193 } FLAC__EntropyCodingMethod_PartitionedRice;
195 extern const unsigned FLAC__ENTROPY_CODING_METHOD_PARTITIONED_RICE_ORDER_LEN; /**< == 4 (bits) */
196 extern const unsigned FLAC__ENTROPY_CODING_METHOD_PARTITIONED_RICE_PARAMETER_LEN; /**< == 4 (bits) */
197 extern const unsigned FLAC__ENTROPY_CODING_METHOD_PARTITIONED_RICE_RAW_LEN; /**< == 5 (bits) */
199 extern const unsigned FLAC__ENTROPY_CODING_METHOD_PARTITIONED_RICE_ESCAPE_PARAMETER;
200 /**< == (1<<FLAC__ENTROPY_CODING_METHOD_PARTITIONED_RICE_PARAMETER_LEN)-1 */
202 /** Header for the entropy coding method. (c.f. <A HREF="../format.html#residual">format specification</A>)
205 FLAC__EntropyCodingMethodType type;
207 FLAC__EntropyCodingMethod_PartitionedRice partitioned_rice;
209 } FLAC__EntropyCodingMethod;
211 extern const unsigned FLAC__ENTROPY_CODING_METHOD_TYPE_LEN; /**< == 2 (bits) */
213 /*****************************************************************************/
215 /** An enumeration of the available subframe types. */
217 FLAC__SUBFRAME_TYPE_CONSTANT = 0, /**< constant signal */
218 FLAC__SUBFRAME_TYPE_VERBATIM = 1, /**< uncompressed signal */
219 FLAC__SUBFRAME_TYPE_FIXED = 2, /**< fixed polynomial prediction */
220 FLAC__SUBFRAME_TYPE_LPC = 3 /**< linear prediction */
221 } FLAC__SubframeType;
223 /** Maps a FLAC__SubframeType to a C string.
225 * Using a FLAC__SubframeType as the index to this array will
226 * give the string equivalent. The contents should not be modified.
228 extern const char * const FLAC__SubframeTypeString[];
231 /** CONSTANT subframe. (c.f. <A HREF="../format.html#subframe_constant">format specification</A>)
234 FLAC__int32 value; /**< The constant signal value. */
235 } FLAC__Subframe_Constant;
238 /** VERBATIM subframe. (c.f. <A HREF="../format.html#subframe_verbatim">format specification</A>)
241 const FLAC__int32 *data; /**< A pointer to verbatim signal. */
242 } FLAC__Subframe_Verbatim;
245 /** FIXED subframe. (c.f. <A HREF="../format.html#subframe_fixed">format specification</A>)
248 FLAC__EntropyCodingMethod entropy_coding_method;
249 /**< The residual coding method. */
252 /**< The polynomial order. */
254 FLAC__int32 warmup[FLAC__MAX_FIXED_ORDER];
255 /**< Warmup samples to prime the predictor, length == order. */
257 const FLAC__int32 *residual;
258 /**< The residual signal, length == (blocksize minus order) samples. */
259 } FLAC__Subframe_Fixed;
262 /** LPC subframe. (c.f. <A HREF="../format.html#subframe_lpc">format specification</A>)
265 FLAC__EntropyCodingMethod entropy_coding_method;
266 /**< The residual coding method. */
269 /**< The FIR order. */
271 unsigned qlp_coeff_precision;
272 /**< Quantized FIR filter coefficient precision in bits. */
274 int quantization_level;
275 /**< The qlp coeff shift needed. */
277 FLAC__int32 qlp_coeff[FLAC__MAX_LPC_ORDER];
278 /**< FIR filter coefficients. */
280 FLAC__int32 warmup[FLAC__MAX_LPC_ORDER];
281 /**< Warmup samples to prime the predictor, length == order. */
283 const FLAC__int32 *residual;
284 /**< The residual signal, length == (blocksize minus order) samples. */
285 } FLAC__Subframe_LPC;
287 extern const unsigned FLAC__SUBFRAME_LPC_QLP_COEFF_PRECISION_LEN; /**< == 4 (bits) */
288 extern const unsigned FLAC__SUBFRAME_LPC_QLP_SHIFT_LEN; /**< == 5 (bits) */
291 /** FLAC subframe structure. (c.f. <A HREF="../format.html#subframe">format specification</A>)
294 FLAC__SubframeType type;
296 FLAC__Subframe_Constant constant;
297 FLAC__Subframe_Fixed fixed;
298 FLAC__Subframe_LPC lpc;
299 FLAC__Subframe_Verbatim verbatim;
301 unsigned wasted_bits;
304 extern const unsigned FLAC__SUBFRAME_ZERO_PAD_LEN; /**< == 1 (bit) */
305 extern const unsigned FLAC__SUBFRAME_TYPE_LEN; /**< == 6 (bits) */
306 extern const unsigned FLAC__SUBFRAME_WASTED_BITS_FLAG_LEN; /**< == 1 (bit) */
308 extern const unsigned FLAC__SUBFRAME_TYPE_CONSTANT_BYTE_ALIGNED_MASK; /* = 0x00 */
309 extern const unsigned FLAC__SUBFRAME_TYPE_VERBATIM_BYTE_ALIGNED_MASK; /* = 0x02 */
310 extern const unsigned FLAC__SUBFRAME_TYPE_FIXED_BYTE_ALIGNED_MASK; /* = 0x10 */
311 extern const unsigned FLAC__SUBFRAME_TYPE_LPC_BYTE_ALIGNED_MASK; /* = 0x40 */
313 /*****************************************************************************/
316 /*****************************************************************************
320 *****************************************************************************/
322 /** An enumeration of the available channel assignments. */
324 FLAC__CHANNEL_ASSIGNMENT_INDEPENDENT = 0, /**< independent channels */
325 FLAC__CHANNEL_ASSIGNMENT_LEFT_SIDE = 1, /**< left+side stereo */
326 FLAC__CHANNEL_ASSIGNMENT_RIGHT_SIDE = 2, /**< right+side stereo */
327 FLAC__CHANNEL_ASSIGNMENT_MID_SIDE = 3 /**< mid+side stereo */
328 } FLAC__ChannelAssignment;
330 /** Maps a FLAC__ChannelAssignment to a C string.
332 * Using a FLAC__ChannelAssignment as the index to this array will
333 * give the string equivalent. The contents should not be modified.
335 extern const char * const FLAC__ChannelAssignmentString[];
337 /** An enumeration of the possible frame numbering methods. */
339 FLAC__FRAME_NUMBER_TYPE_FRAME_NUMBER, /**< number contains the frame number */
340 FLAC__FRAME_NUMBER_TYPE_SAMPLE_NUMBER /**< number contains the sample number of first sample in frame */
341 } FLAC__FrameNumberType;
343 /** Maps a FLAC__FrameNumberType to a C string.
345 * Using a FLAC__FrameNumberType as the index to this array will
346 * give the string equivalent. The contents should not be modified.
348 extern const char * const FLAC__FrameNumberTypeString[];
351 /** FLAC frame header structure. (c.f. <A HREF="../format.html#frame_header">format specification</A>)
355 /**< The number of samples per subframe. */
357 unsigned sample_rate;
358 /**< The sample rate in Hz. */
361 /**< The number of channels (== number of subframes). */
363 FLAC__ChannelAssignment channel_assignment;
364 /**< The channel assignment for the frame. */
366 unsigned bits_per_sample;
367 /**< The sample resolution. */
369 FLAC__FrameNumberType number_type;
370 /**< The numbering scheme used for the frame. */
373 FLAC__uint32 frame_number;
374 FLAC__uint64 sample_number;
376 /**< The frame number or sample number of first sample in frame;
377 * use the \a number_type value to determine which to use. */
380 /**< CRC-8 (polynomial = x^8 + x^2 + x^1 + x^0, initialized with 0)
381 * of the raw frame header bytes, meaning everything before the CRC byte
382 * including the sync code.
386 extern const unsigned FLAC__FRAME_HEADER_SYNC; /**< == 0x3ffe; the frame header sync code */
387 extern const unsigned FLAC__FRAME_HEADER_SYNC_LEN; /**< == 14 (bits) */
388 extern const unsigned FLAC__FRAME_HEADER_RESERVED_LEN; /**< == 2 (bits) */
389 extern const unsigned FLAC__FRAME_HEADER_BLOCK_SIZE_LEN; /**< == 4 (bits) */
390 extern const unsigned FLAC__FRAME_HEADER_SAMPLE_RATE_LEN; /**< == 4 (bits) */
391 extern const unsigned FLAC__FRAME_HEADER_CHANNEL_ASSIGNMENT_LEN; /**< == 4 (bits) */
392 extern const unsigned FLAC__FRAME_HEADER_BITS_PER_SAMPLE_LEN; /**< == 3 (bits) */
393 extern const unsigned FLAC__FRAME_HEADER_ZERO_PAD_LEN; /**< == 1 (bit) */
394 extern const unsigned FLAC__FRAME_HEADER_CRC_LEN; /**< == 8 (bits) */
397 /** FLAC frame footer structure. (c.f. <A HREF="../format.html#frame_footer">format specification</A>)
401 /**< CRC-16 (polynomial = x^16 + x^15 + x^2 + x^0, initialized with
402 * 0) of the bytes before the crc, back to and including the frame header
407 extern const unsigned FLAC__FRAME_FOOTER_CRC_LEN; /**< == 16 (bits) */
410 /** FLAC frame structure. (c.f. <A HREF="../format.html#frame">format specification</A>)
413 FLAC__FrameHeader header;
414 FLAC__Subframe subframes[FLAC__MAX_CHANNELS];
415 FLAC__FrameFooter footer;
418 /*****************************************************************************/
421 /*****************************************************************************
423 * Meta-data structures
425 *****************************************************************************/
427 /** An enumeration of the available metadata block types. */
430 FLAC__METADATA_TYPE_STREAMINFO = 0,
431 /**< <A HREF="../format.html#metadata_block_streaminfo">STREAMINFO</A> block */
433 FLAC__METADATA_TYPE_PADDING = 1,
434 /**< <A HREF="../format.html#metadata_block_padding"PADDING</A> block */
436 FLAC__METADATA_TYPE_APPLICATION = 2,
437 /**< <A HREF="../format.html#metadata_block_application"APPLICATION</A> block */
439 FLAC__METADATA_TYPE_SEEKTABLE = 3,
440 /**< <A HREF="../format.html#metadata_block_seektable"SEEKTABLE</A> block */
442 FLAC__METADATA_TYPE_VORBIS_COMMENT = 4,
443 /**< <A HREF="../format.html#metadata_block_vorbis_comment"VORBISCOMMENT</A> block */
445 } FLAC__MetadataType;
447 /** Maps a FLAC__MetadataType to a C string.
449 * Using a FLAC__MetadataType as the index to this array will
450 * give the string equivalent. The contents should not be modified.
452 extern const char * const FLAC__MetadataTypeString[];
455 /** FLAC STREAMINFO structure. (c.f. <A HREF="../format.html#metadata_block_streaminfo">format specification</A>)
458 unsigned min_blocksize, max_blocksize;
459 unsigned min_framesize, max_framesize;
460 unsigned sample_rate;
462 unsigned bits_per_sample;
463 FLAC__uint64 total_samples;
464 FLAC__byte md5sum[16];
465 } FLAC__StreamMetadata_StreamInfo;
467 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_MIN_BLOCK_SIZE_LEN; /**< == 16 (bits) */
468 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_MAX_BLOCK_SIZE_LEN; /**< == 16 (bits) */
469 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_MIN_FRAME_SIZE_LEN; /**< == 24 (bits) */
470 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_MAX_FRAME_SIZE_LEN; /**< == 24 (bits) */
471 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_SAMPLE_RATE_LEN; /**< == 20 (bits) */
472 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_CHANNELS_LEN; /**< == 3 (bits) */
473 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_BITS_PER_SAMPLE_LEN; /**< == 5 (bits) */
474 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_TOTAL_SAMPLES_LEN; /**< == 36 (bits) */
475 extern const unsigned FLAC__STREAM_METADATA_STREAMINFO_MD5SUM_LEN; /**< == 128 (bits) */
477 /** The total stream length of the STREAMINFO block in bytes. */
478 #define FLAC__STREAM_METADATA_STREAMINFO_LENGTH (34u)
480 /** FLAC PADDING structure. (c.f. <A HREF="../format.html#metadata_block_padding">format specification</A>)
484 /**< Conceptually this is an empty struct since we don't store the
485 * padding bytes. Empty structs are not allowed by some C compilers,
488 } FLAC__StreamMetadata_Padding;
491 /** FLAC APPLICATION structure. (c.f. <A HREF="../format.html#metadata_block_application">format specification</A>)
496 } FLAC__StreamMetadata_Application;
498 extern const unsigned FLAC__STREAM_METADATA_APPLICATION_ID_LEN; /**< == 32 (bits) */
500 /** SeekPoint structure used in SEEKTABLE blocks. (c.f. <A HREF="../format.html#seekpoint">format specification</A>)
503 FLAC__uint64 sample_number;
504 /**< The sample number of the target frame. */
506 FLAC__uint64 stream_offset;
507 /**< The offset, in bytes, of the target frame with respect to
508 * beginning of the first frame. */
510 unsigned frame_samples;
511 /**< The number of samples in the target frame. */
512 } FLAC__StreamMetadata_SeekPoint;
514 extern const unsigned FLAC__STREAM_METADATA_SEEKPOINT_SAMPLE_NUMBER_LEN; /**< == 64 (bits) */
515 extern const unsigned FLAC__STREAM_METADATA_SEEKPOINT_STREAM_OFFSET_LEN; /**< == 64 (bits) */
516 extern const unsigned FLAC__STREAM_METADATA_SEEKPOINT_FRAME_SAMPLES_LEN; /**< == 16 (bits) */
518 /** The total stream length of a seek point in bytes. */
519 #define FLAC__STREAM_METADATA_SEEKPOINT_LENGTH (18u)
521 /** The value used in the \a sample_number field of
522 * FLAC__StreamMetadataSeekPoint used to indicate a placeholder
523 * point (== 0xffffffffffffffff).
525 extern const FLAC__uint64 FLAC__STREAM_METADATA_SEEKPOINT_PLACEHOLDER;
528 /** FLAC SEEKTABLE structure. (c.f. <A HREF="../format.html#metadata_block_seektable">format specification</A>)
530 * \note From the format specification:
531 * - The seek points must be sorted by ascending sample number.
532 * - Each seek point's sample number must be the first sample of the
534 * - Each seek point's sample number must be unique within the table.
535 * - Existence of a SEEKTABLE block implies a correct setting of
536 * total_samples in the stream_info block.
537 * - Behavior is undefined when more than one SEEKTABLE block is
538 * present in a stream.
542 FLAC__StreamMetadata_SeekPoint *points;
543 } FLAC__StreamMetadata_SeekTable;
546 /** Vorbis comment entry structure used in VORBIS_COMMENT blocks. (c.f. <A HREF="../format.html#metadata_block_vorbis_comment">format specification</A>)
551 } FLAC__StreamMetadata_VorbisComment_Entry;
553 extern const unsigned FLAC__STREAM_METADATA_VORBIS_COMMENT_ENTRY_LENGTH_LEN; /**< == 32 (bits) */
556 /** FLAC VORBIS_COMMENT structure. (c.f. <A HREF="../format.html#metadata_block_vorbis_comment">format specification</A>)
559 FLAC__StreamMetadata_VorbisComment_Entry vendor_string;
560 FLAC__uint32 num_comments;
561 FLAC__StreamMetadata_VorbisComment_Entry *comments;
562 } FLAC__StreamMetadata_VorbisComment;
564 extern const unsigned FLAC__STREAM_METADATA_VORBIS_COMMENT_NUM_COMMENTS_LEN; /**< == 32 (bits) */
567 /** FLAC metadata block structure. (c.f. <A HREF="../format.html#metadata_block">format specification</A>)
570 FLAC__MetadataType type;
571 /**< The type of the metadata block; used determine which member of the
572 * \a data union to dereference. */
575 /**< \c true if this metadata block is the last, else \a false */
578 /**< Length, in bytes, of the block data as it appears in the stream. */
581 FLAC__StreamMetadata_StreamInfo stream_info;
582 FLAC__StreamMetadata_Padding padding;
583 FLAC__StreamMetadata_Application application;
584 FLAC__StreamMetadata_SeekTable seek_table;
585 FLAC__StreamMetadata_VorbisComment vorbis_comment;
587 /**< Polymorphic block data; use the \a type value to determine which
589 } FLAC__StreamMetadata;
591 extern const unsigned FLAC__STREAM_METADATA_IS_LAST_LEN; /**< == 1 (bit) */
592 extern const unsigned FLAC__STREAM_METADATA_TYPE_LEN; /**< == 7 (bits) */
593 extern const unsigned FLAC__STREAM_METADATA_LENGTH_LEN; /**< == 24 (bits) */
595 /** The total stream length of a metadata block header in bytes. */
596 #define FLAC__STREAM_METADATA_HEADER_LENGTH (4u)
598 /*****************************************************************************/
601 /*****************************************************************************
605 *****************************************************************************/
607 /** Tests that a sample rate is valid for FLAC. Since the rules for valid
608 * sample rates are slightly complex, they are encapsulated in this function.
610 * \param sample_rate The sample rate to test for compliance.
612 * \c true if the given sample rate conforms to the specification, else
615 FLAC__bool FLAC__format_sample_rate_is_valid(unsigned sample_rate);
617 /** Check a seek table to see if it conforms to the FLAC specification.
618 * See the format specification for limits on the contents of the
621 * \param seek_table A pointer to a seek table to be checked.
623 * \code seek_table != NULL \endcode
625 * \c false if seek table is illegal, else \c true.
627 FLAC__bool FLAC__format_seektable_is_legal(const FLAC__StreamMetadata_SeekTable *seek_table);
629 /** Sort a seek table's seek points according to the format specification.
630 * This includes a "unique-ification" step to remove duplicates, i.e.
631 * seek points with identical \a sample_number values. Duplicate seek
632 * points are converted into placeholder points and sorted to the end of
635 * \param seek_table A pointer to a seek table to be sorted.
637 * \code seek_table != NULL \endcode
639 * The number of duplicate seek points converted into placeholders.
641 unsigned FLAC__format_seektable_sort(FLAC__StreamMetadata_SeekTable *seek_table);