0181379b78eb155f75b09aea776f8c79c505c997
[libav.git] / libavutil / opt.h
1 /*
2 * AVOptions
3 * copyright (c) 2005 Michael Niedermayer <michaelni@gmx.at>
4 *
5 * This file is part of Libav.
6 *
7 * Libav is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
11 *
12 * Libav is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with Libav; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 */
21
22 #ifndef AVUTIL_OPT_H
23 #define AVUTIL_OPT_H
24
25 /**
26 * @file
27 * AVOptions
28 */
29
30 #include "rational.h"
31 #include "avutil.h"
32 #include "dict.h"
33 #include "log.h"
34
35 /**
36 * @defgroup avoptions AVOptions
37 * @ingroup lavu_data
38 * @{
39 * AVOptions provide a generic system to declare options on arbitrary structs
40 * ("objects"). An option can have a help text, a type and a range of possible
41 * values. Options may then be enumerated, read and written to.
42 *
43 * @section avoptions_implement Implementing AVOptions
44 * This section describes how to add AVOptions capabilities to a struct.
45 *
46 * All AVOptions-related information is stored in an AVClass. Therefore
47 * the first member of the struct must be a pointer to an AVClass describing it.
48 * The option field of the AVClass must be set to a NULL-terminated static array
49 * of AVOptions. Each AVOption must have a non-empty name, a type, a default
50 * value and for number-type AVOptions also a range of allowed values. It must
51 * also declare an offset in bytes from the start of the struct, where the field
52 * associated with this AVOption is located. Other fields in the AVOption struct
53 * should also be set when applicable, but are not required.
54 *
55 * The following example illustrates an AVOptions-enabled struct:
56 * @code
57 * typedef struct test_struct {
58 * AVClass *class;
59 * int int_opt;
60 * char *str_opt;
61 * uint8_t *bin_opt;
62 * int bin_len;
63 * } test_struct;
64 *
65 * static const AVOption test_options[] = {
66 * { "test_int", "This is a test option of int type.", offsetof(test_struct, int_opt),
67 * AV_OPT_TYPE_INT, { .i64 = -1 }, INT_MIN, INT_MAX },
68 * { "test_str", "This is a test option of string type.", offsetof(test_struct, str_opt),
69 * AV_OPT_TYPE_STRING },
70 * { "test_bin", "This is a test option of binary type.", offsetof(test_struct, bin_opt),
71 * AV_OPT_TYPE_BINARY },
72 * { NULL },
73 * };
74 *
75 * static const AVClass test_class = {
76 * .class_name = "test class",
77 * .item_name = av_default_item_name,
78 * .option = test_options,
79 * .version = LIBAVUTIL_VERSION_INT,
80 * };
81 * @endcode
82 *
83 * Next, when allocating your struct, you must ensure that the AVClass pointer
84 * is set to the correct value. Then, av_opt_set_defaults() must be called to
85 * initialize defaults. After that the struct is ready to be used with the
86 * AVOptions API.
87 *
88 * When cleaning up, you may use the av_opt_free() function to automatically
89 * free all the allocated string and binary options.
90 *
91 * Continuing with the above example:
92 *
93 * @code
94 * test_struct *alloc_test_struct(void)
95 * {
96 * test_struct *ret = av_malloc(sizeof(*ret));
97 * ret->class = &test_class;
98 * av_opt_set_defaults(ret);
99 * return ret;
100 * }
101 * void free_test_struct(test_struct **foo)
102 * {
103 * av_opt_free(*foo);
104 * av_freep(foo);
105 * }
106 * @endcode
107 *
108 * @subsection avoptions_implement_nesting Nesting
109 * It may happen that an AVOptions-enabled struct contains another
110 * AVOptions-enabled struct as a member (e.g. AVCodecContext in
111 * libavcodec exports generic options, while its priv_data field exports
112 * codec-specific options). In such a case, it is possible to set up the
113 * parent struct to export a child's options. To do that, simply
114 * implement AVClass.child_next() and AVClass.child_class_next() in the
115 * parent struct's AVClass.
116 * Assuming that the test_struct from above now also contains a
117 * child_struct field:
118 *
119 * @code
120 * typedef struct child_struct {
121 * AVClass *class;
122 * int flags_opt;
123 * } child_struct;
124 * static const AVOption child_opts[] = {
125 * { "test_flags", "This is a test option of flags type.",
126 * offsetof(child_struct, flags_opt), AV_OPT_TYPE_FLAGS, { .i64 = 0 }, INT_MIN, INT_MAX },
127 * { NULL },
128 * };
129 * static const AVClass child_class = {
130 * .class_name = "child class",
131 * .item_name = av_default_item_name,
132 * .option = child_opts,
133 * .version = LIBAVUTIL_VERSION_INT,
134 * };
135 *
136 * void *child_next(void *obj, void *prev)
137 * {
138 * test_struct *t = obj;
139 * if (!prev && t->child_struct)
140 * return t->child_struct;
141 * return NULL
142 * }
143 * const AVClass child_class_next(const AVClass *prev)
144 * {
145 * return prev ? NULL : &child_class;
146 * }
147 * @endcode
148 * Putting child_next() and child_class_next() as defined above into
149 * test_class will now make child_struct's options accessible through
150 * test_struct (again, proper setup as described above needs to be done on
151 * child_struct right after it is created).
152 *
153 * From the above example it might not be clear why both child_next()
154 * and child_class_next() are needed. The distinction is that child_next()
155 * iterates over actually existing objects, while child_class_next()
156 * iterates over all possible child classes. E.g. if an AVCodecContext
157 * was initialized to use a codec which has private options, then its
158 * child_next() will return AVCodecContext.priv_data and finish
159 * iterating. OTOH child_class_next() on AVCodecContext.av_class will
160 * iterate over all available codecs with private options.
161 *
162 * @subsection avoptions_implement_named_constants Named constants
163 * It is possible to create named constants for options. Simply set the unit
164 * field of the option the constants should apply to to a string and
165 * create the constants themselves as options of type AV_OPT_TYPE_CONST
166 * with their unit field set to the same string.
167 * Their default_val field should contain the value of the named
168 * constant.
169 * For example, to add some named constants for the test_flags option
170 * above, put the following into the child_opts array:
171 * @code
172 * { "test_flags", "This is a test option of flags type.",
173 * offsetof(child_struct, flags_opt), AV_OPT_TYPE_FLAGS, { .i64 = 0 }, INT_MIN, INT_MAX, "test_unit" },
174 * { "flag1", "This is a flag with value 16", 0, AV_OPT_TYPE_CONST, { .i64 = 16 }, 0, 0, "test_unit" },
175 * @endcode
176 *
177 * @section avoptions_use Using AVOptions
178 * This section deals with accessing options in an AVOptions-enabled struct.
179 * Such structs in Libav are e.g. AVCodecContext in libavcodec or
180 * AVFormatContext in libavformat.
181 *
182 * @subsection avoptions_use_examine Examining AVOptions
183 * The basic functions for examining options are av_opt_next(), which iterates
184 * over all options defined for one object, and av_opt_find(), which searches
185 * for an option with the given name.
186 *
187 * The situation is more complicated with nesting. An AVOptions-enabled struct
188 * may have AVOptions-enabled children. Passing the AV_OPT_SEARCH_CHILDREN flag
189 * to av_opt_find() will make the function search children recursively.
190 *
191 * For enumerating there are basically two cases. The first is when you want to
192 * get all options that may potentially exist on the struct and its children
193 * (e.g. when constructing documentation). In that case you should call
194 * av_opt_child_class_next() recursively on the parent struct's AVClass. The
195 * second case is when you have an already initialized struct with all its
196 * children and you want to get all options that can be actually written or read
197 * from it. In that case you should call av_opt_child_next() recursively (and
198 * av_opt_next() on each result).
199 *
200 * @subsection avoptions_use_get_set Reading and writing AVOptions
201 * When setting options, you often have a string read directly from the
202 * user. In such a case, simply passing it to av_opt_set() is enough. For
203 * non-string type options, av_opt_set() will parse the string according to the
204 * option type.
205 *
206 * Similarly av_opt_get() will read any option type and convert it to a string
207 * which will be returned. Do not forget that the string is allocated, so you
208 * have to free it with av_free().
209 *
210 * In some cases it may be more convenient to put all options into an
211 * AVDictionary and call av_opt_set_dict() on it. A specific case of this
212 * are the format/codec open functions in lavf/lavc which take a dictionary
213 * filled with option as a parameter. This allows to set some options
214 * that cannot be set otherwise, since e.g. the input file format is not known
215 * before the file is actually opened.
216 */
217
218 enum AVOptionType{
219 AV_OPT_TYPE_FLAGS,
220 AV_OPT_TYPE_INT,
221 AV_OPT_TYPE_INT64,
222 AV_OPT_TYPE_DOUBLE,
223 AV_OPT_TYPE_FLOAT,
224 AV_OPT_TYPE_STRING,
225 AV_OPT_TYPE_RATIONAL,
226 AV_OPT_TYPE_BINARY, ///< offset must point to a pointer immediately followed by an int for the length
227 AV_OPT_TYPE_CONST = 128,
228 };
229
230 /**
231 * AVOption
232 */
233 typedef struct AVOption {
234 const char *name;
235
236 /**
237 * short English help text
238 * @todo What about other languages?
239 */
240 const char *help;
241
242 /**
243 * The offset relative to the context structure where the option
244 * value is stored. It should be 0 for named constants.
245 */
246 int offset;
247 enum AVOptionType type;
248
249 /**
250 * the default value for scalar options
251 */
252 union {
253 int64_t i64;
254 double dbl;
255 const char *str;
256 /* TODO those are unused now */
257 AVRational q;
258 } default_val;
259 double min; ///< minimum valid value for the option
260 double max; ///< maximum valid value for the option
261
262 int flags;
263 #define AV_OPT_FLAG_ENCODING_PARAM 1 ///< a generic parameter which can be set by the user for muxing or encoding
264 #define AV_OPT_FLAG_DECODING_PARAM 2 ///< a generic parameter which can be set by the user for demuxing or decoding
265 #define AV_OPT_FLAG_METADATA 4 ///< some data extracted or inserted into the file like title, comment, ...
266 #define AV_OPT_FLAG_AUDIO_PARAM 8
267 #define AV_OPT_FLAG_VIDEO_PARAM 16
268 #define AV_OPT_FLAG_SUBTITLE_PARAM 32
269 //FIXME think about enc-audio, ... style flags
270
271 /**
272 * The logical unit to which the option belongs. Non-constant
273 * options and corresponding named constants share the same
274 * unit. May be NULL.
275 */
276 const char *unit;
277 } AVOption;
278
279 /**
280 * Show the obj options.
281 *
282 * @param req_flags requested flags for the options to show. Show only the
283 * options for which it is opt->flags & req_flags.
284 * @param rej_flags rejected flags for the options to show. Show only the
285 * options for which it is !(opt->flags & req_flags).
286 * @param av_log_obj log context to use for showing the options
287 */
288 int av_opt_show2(void *obj, void *av_log_obj, int req_flags, int rej_flags);
289
290 /**
291 * Set the values of all AVOption fields to their default values.
292 *
293 * @param s an AVOption-enabled struct (its first member must be a pointer to AVClass)
294 */
295 void av_opt_set_defaults(void *s);
296
297 /**
298 * Parse the key/value pairs list in opts. For each key/value pair
299 * found, stores the value in the field in ctx that is named like the
300 * key. ctx must be an AVClass context, storing is done using
301 * AVOptions.
302 *
303 * @param key_val_sep a 0-terminated list of characters used to
304 * separate key from value
305 * @param pairs_sep a 0-terminated list of characters used to separate
306 * two pairs from each other
307 * @return the number of successfully set key/value pairs, or a negative
308 * value corresponding to an AVERROR code in case of error:
309 * AVERROR(EINVAL) if opts cannot be parsed,
310 * the error code issued by av_set_string3() if a key/value pair
311 * cannot be set
312 */
313 int av_set_options_string(void *ctx, const char *opts,
314 const char *key_val_sep, const char *pairs_sep);
315
316 /**
317 * Free all string and binary options in obj.
318 */
319 void av_opt_free(void *obj);
320
321 /**
322 * Check whether a particular flag is set in a flags field.
323 *
324 * @param field_name the name of the flag field option
325 * @param flag_name the name of the flag to check
326 * @return non-zero if the flag is set, zero if the flag isn't set,
327 * isn't of the right type, or the flags field doesn't exist.
328 */
329 int av_opt_flag_is_set(void *obj, const char *field_name, const char *flag_name);
330
331 /*
332 * Set all the options from a given dictionary on an object.
333 *
334 * @param obj a struct whose first element is a pointer to AVClass
335 * @param options options to process. This dictionary will be freed and replaced
336 * by a new one containing all options not found in obj.
337 * Of course this new dictionary needs to be freed by caller
338 * with av_dict_free().
339 *
340 * @return 0 on success, a negative AVERROR if some option was found in obj,
341 * but could not be set.
342 *
343 * @see av_dict_copy()
344 */
345 int av_opt_set_dict(void *obj, struct AVDictionary **options);
346
347 /**
348 * @defgroup opt_eval_funcs Evaluating option strings
349 * @{
350 * This group of functions can be used to evaluate option strings
351 * and get numbers out of them. They do the same thing as av_opt_set(),
352 * except the result is written into the caller-supplied pointer.
353 *
354 * @param obj a struct whose first element is a pointer to AVClass.
355 * @param o an option for which the string is to be evaluated.
356 * @param val string to be evaluated.
357 * @param *_out value of the string will be written here.
358 *
359 * @return 0 on success, a negative number on failure.
360 */
361 int av_opt_eval_flags (void *obj, const AVOption *o, const char *val, int *flags_out);
362 int av_opt_eval_int (void *obj, const AVOption *o, const char *val, int *int_out);
363 int av_opt_eval_int64 (void *obj, const AVOption *o, const char *val, int64_t *int64_out);
364 int av_opt_eval_float (void *obj, const AVOption *o, const char *val, float *float_out);
365 int av_opt_eval_double(void *obj, const AVOption *o, const char *val, double *double_out);
366 int av_opt_eval_q (void *obj, const AVOption *o, const char *val, AVRational *q_out);
367 /**
368 * @}
369 */
370
371 #define AV_OPT_SEARCH_CHILDREN 0x0001 /**< Search in possible children of the
372 given object first. */
373 /**
374 * The obj passed to av_opt_find() is fake -- only a double pointer to AVClass
375 * instead of a required pointer to a struct containing AVClass. This is
376 * useful for searching for options without needing to allocate the corresponding
377 * object.
378 */
379 #define AV_OPT_SEARCH_FAKE_OBJ 0x0002
380
381 /**
382 * Look for an option in an object. Consider only options which
383 * have all the specified flags set.
384 *
385 * @param[in] obj A pointer to a struct whose first element is a
386 * pointer to an AVClass.
387 * Alternatively a double pointer to an AVClass, if
388 * AV_OPT_SEARCH_FAKE_OBJ search flag is set.
389 * @param[in] name The name of the option to look for.
390 * @param[in] unit When searching for named constants, name of the unit
391 * it belongs to.
392 * @param opt_flags Find only options with all the specified flags set (AV_OPT_FLAG).
393 * @param search_flags A combination of AV_OPT_SEARCH_*.
394 *
395 * @return A pointer to the option found, or NULL if no option
396 * was found.
397 *
398 * @note Options found with AV_OPT_SEARCH_CHILDREN flag may not be settable
399 * directly with av_set_string3(). Use special calls which take an options
400 * AVDictionary (e.g. avformat_open_input()) to set options found with this
401 * flag.
402 */
403 const AVOption *av_opt_find(void *obj, const char *name, const char *unit,
404 int opt_flags, int search_flags);
405
406 /**
407 * Look for an option in an object. Consider only options which
408 * have all the specified flags set.
409 *
410 * @param[in] obj A pointer to a struct whose first element is a
411 * pointer to an AVClass.
412 * Alternatively a double pointer to an AVClass, if
413 * AV_OPT_SEARCH_FAKE_OBJ search flag is set.
414 * @param[in] name The name of the option to look for.
415 * @param[in] unit When searching for named constants, name of the unit
416 * it belongs to.
417 * @param opt_flags Find only options with all the specified flags set (AV_OPT_FLAG).
418 * @param search_flags A combination of AV_OPT_SEARCH_*.
419 * @param[out] target_obj if non-NULL, an object to which the option belongs will be
420 * written here. It may be different from obj if AV_OPT_SEARCH_CHILDREN is present
421 * in search_flags. This parameter is ignored if search_flags contain
422 * AV_OPT_SEARCH_FAKE_OBJ.
423 *
424 * @return A pointer to the option found, or NULL if no option
425 * was found.
426 */
427 const AVOption *av_opt_find2(void *obj, const char *name, const char *unit,
428 int opt_flags, int search_flags, void **target_obj);
429
430 /**
431 * Iterate over all AVOptions belonging to obj.
432 *
433 * @param obj an AVOptions-enabled struct or a double pointer to an
434 * AVClass describing it.
435 * @param prev result of the previous call to av_opt_next() on this object
436 * or NULL
437 * @return next AVOption or NULL
438 */
439 const AVOption *av_opt_next(void *obj, const AVOption *prev);
440
441 /**
442 * Iterate over AVOptions-enabled children of obj.
443 *
444 * @param prev result of a previous call to this function or NULL
445 * @return next AVOptions-enabled child or NULL
446 */
447 void *av_opt_child_next(void *obj, void *prev);
448
449 /**
450 * Iterate over potential AVOptions-enabled children of parent.
451 *
452 * @param prev result of a previous call to this function or NULL
453 * @return AVClass corresponding to next potential child or NULL
454 */
455 const AVClass *av_opt_child_class_next(const AVClass *parent, const AVClass *prev);
456
457 /**
458 * @defgroup opt_set_funcs Option setting functions
459 * @{
460 * Those functions set the field of obj with the given name to value.
461 *
462 * @param[in] obj A struct whose first element is a pointer to an AVClass.
463 * @param[in] name the name of the field to set
464 * @param[in] val The value to set. In case of av_opt_set() if the field is not
465 * of a string type, then the given string is parsed.
466 * SI postfixes and some named scalars are supported.
467 * If the field is of a numeric type, it has to be a numeric or named
468 * scalar. Behavior with more than one scalar and +- infix operators
469 * is undefined.
470 * If the field is of a flags type, it has to be a sequence of numeric
471 * scalars or named flags separated by '+' or '-'. Prefixing a flag
472 * with '+' causes it to be set without affecting the other flags;
473 * similarly, '-' unsets a flag.
474 * @param search_flags flags passed to av_opt_find2. I.e. if AV_OPT_SEARCH_CHILDREN
475 * is passed here, then the option may be set on a child of obj.
476 *
477 * @return 0 if the value has been set, or an AVERROR code in case of
478 * error:
479 * AVERROR_OPTION_NOT_FOUND if no matching option exists
480 * AVERROR(ERANGE) if the value is out of range
481 * AVERROR(EINVAL) if the value is not valid
482 */
483 int av_opt_set (void *obj, const char *name, const char *val, int search_flags);
484 int av_opt_set_int (void *obj, const char *name, int64_t val, int search_flags);
485 int av_opt_set_double(void *obj, const char *name, double val, int search_flags);
486 int av_opt_set_q (void *obj, const char *name, AVRational val, int search_flags);
487 int av_opt_set_bin (void *obj, const char *name, const uint8_t *val, int size, int search_flags);
488 /**
489 * @}
490 */
491
492 /**
493 * @defgroup opt_get_funcs Option getting functions
494 * @{
495 * Those functions get a value of the option with the given name from an object.
496 *
497 * @param[in] obj a struct whose first element is a pointer to an AVClass.
498 * @param[in] name name of the option to get.
499 * @param[in] search_flags flags passed to av_opt_find2. I.e. if AV_OPT_SEARCH_CHILDREN
500 * is passed here, then the option may be found in a child of obj.
501 * @param[out] out_val value of the option will be written here
502 * @return 0 on success, a negative error code otherwise
503 */
504 /**
505 * @note the returned string will av_malloc()ed and must be av_free()ed by the caller
506 */
507 int av_opt_get (void *obj, const char *name, int search_flags, uint8_t **out_val);
508 int av_opt_get_int (void *obj, const char *name, int search_flags, int64_t *out_val);
509 int av_opt_get_double(void *obj, const char *name, int search_flags, double *out_val);
510 int av_opt_get_q (void *obj, const char *name, int search_flags, AVRational *out_val);
511 /**
512 * @}
513 * @}
514 */
515
516 #endif /* AVUTIL_OPT_H */