AVOptions provide a generic system to declare options on arbitrary structs ("objects"). More...
Modules | |
Evaluating option strings | |
This group of functions can be used to evaluate option strings and get numbers out of them. | |
Option setting functions | |
Those functions set the field of obj with the given name to value. | |
Option getting functions | |
Those functions get a value of the option with the given name from an object. |
Data Structures | |
struct | AVOption |
AVOption. More... |
Macros | |
#define | AV_OPT_SEARCH_CHILDREN 0x0001 |
Search in possible children of the given object first. | |
#define | AV_OPT_SEARCH_FAKE_OBJ 0x0002 |
The obj passed to av_opt_find() is fake – only a double pointer to AVClass instead of a required pointer to a struct containing AVClass. |
Typedefs | |
typedef struct AVOption | AVOption |
AVOption. |
Functions | |
attribute_deprecated const AVOption * | av_find_opt (void *obj, const char *name, const char *unit, int mask, int flags) |
Look for an option in obj. | |
attribute_deprecated int | av_set_string3 (void *obj, const char *name, const char *val, int alloc, const AVOption **o_out) |
Set the field of obj with the given name to value. | |
attribute_deprecated const AVOption * | av_set_double (void *obj, const char *name, double n) |
attribute_deprecated const AVOption * | av_set_q (void *obj, const char *name, AVRational n) |
attribute_deprecated const AVOption * | av_set_int (void *obj, const char *name, int64_t n) |
attribute_deprecated double | av_get_double (void *obj, const char *name, const AVOption **o_out) |
attribute_deprecated AVRational | av_get_q (void *obj, const char *name, const AVOption **o_out) |
attribute_deprecated int64_t | av_get_int (void *obj, const char *name, const AVOption **o_out) |
attribute_deprecated const char * | av_get_string (void *obj, const char *name, const AVOption **o_out, char *buf, int buf_len) |
attribute_deprecated const AVOption * | av_next_option (void *obj, const AVOption *last) |
int | av_opt_show2 (void *obj, void *av_log_obj, int req_flags, int rej_flags) |
Show the obj options. | |
void | av_opt_set_defaults (void *s) |
Set the values of all AVOption fields to their default values. | |
attribute_deprecated void | av_opt_set_defaults2 (void *s, int mask, int flags) |
int | av_set_options_string (void *ctx, const char *opts, const char *key_val_sep, const char *pairs_sep) |
Parse the key/value pairs list in opts. | |
void | av_opt_free (void *obj) |
Free all string and binary options in obj. | |
int | av_opt_flag_is_set (void *obj, const char *field_name, const char *flag_name) |
Check whether a particular flag is set in a flags field. | |
int | av_opt_set_dict (void *obj, struct AVDictionary **options) |
const AVOption * | av_opt_find (void *obj, const char *name, const char *unit, int opt_flags, int search_flags) |
Look for an option in an object. | |
const AVOption * | av_opt_find2 (void *obj, const char *name, const char *unit, int opt_flags, int search_flags, void **target_obj) |
Look for an option in an object. | |
const AVOption * | av_opt_next (void *obj, const AVOption *prev) |
Iterate over all AVOptions belonging to obj. | |
void * | av_opt_child_next (void *obj, void *prev) |
Iterate over AVOptions-enabled children of obj. | |
const AVClass * | av_opt_child_class_next (const AVClass *parent, const AVClass *prev) |
Iterate over potential AVOptions-enabled children of parent. |
AVOptions provide a generic system to declare options on arbitrary structs ("objects").
An option can have a help text, a type and a range of possible values. Options may then be enumerated, read and written to.
This section describes how to add AVOptions capabilities to a struct.
All AVOptions-related information is stored in an AVClass. Therefore the first member of the struct must be a pointer to an AVClass describing it. The option field of the AVClass must be set to a NULL-terminated static array of AVOptions. Each AVOption must have a non-empty name, a type, a default value and for number-type AVOptions also a range of allowed values. It must also declare an offset in bytes from the start of the struct, where the field associated with this AVOption is located. Other fields in the AVOption struct should also be set when applicable, but are not required.
The following example illustrates an AVOptions-enabled struct:
Next, when allocating your struct, you must ensure that the AVClass pointer is set to the correct value. Then, av_opt_set_defaults() must be called to initialize defaults. After that the struct is ready to be used with the AVOptions API.
When cleaning up, you may use the av_opt_free() function to automatically free all the allocated string and binary options.
Continuing with the above example:
It may happen that an AVOptions-enabled struct contains another AVOptions-enabled struct as a member (e.g. AVCodecContext in libavcodec exports generic options, while its priv_data field exports codec-specific options). In such a case, it is possible to set up the parent struct to export a child's options. To do that, simply implement AVClass.child_next() and AVClass.child_class_next() in the parent struct's AVClass. Assuming that the test_struct from above now also contains a child_struct field:
Putting child_next() and child_class_next() as defined above into test_class will now make child_struct's options accessible through test_struct (again, proper setup as described above needs to be done on child_struct right after it is created).
From the above example it might not be clear why both child_next() and child_class_next() are needed. The distinction is that child_next() iterates over actually existing objects, while child_class_next() iterates over all possible child classes. E.g. if an AVCodecContext was initialized to use a codec which has private options, then its child_next() will return AVCodecContext.priv_data and finish iterating. OTOH child_class_next() on AVCodecContext.av_class will iterate over all available codecs with private options.
It is possible to create named constants for options. Simply set the unit field of the option the constants should apply to to a string and create the constants themselves as options of type AV_OPT_TYPE_CONST with their unit field set to the same string. Their default_val field should contain the value of the named constant. For example, to add some named constants for the test_flags option above, put the following into the child_opts array:
This section deals with accessing options in an AVOptions-enabled struct. Such structs in Libav are e.g. AVCodecContext in libavcodec or AVFormatContext in libavformat.
The basic functions for examining options are av_opt_next(), which iterates over all options defined for one object, and av_opt_find(), which searches for an option with the given name.
The situation is more complicated with nesting. An AVOptions-enabled struct may have AVOptions-enabled children. Passing the AV_OPT_SEARCH_CHILDREN flag to av_opt_find() will make the function search children recursively.
For enumerating there are basically two cases. The first is when you want to get all options that may potentially exist on the struct and its children (e.g. when constructing documentation). In that case you should call av_opt_child_class_next() recursively on the parent struct's AVClass. The second case is when you have an already initialized struct with all its children and you want to get all options that can be actually written or read from it. In that case you should call av_opt_child_next() recursively (and av_opt_next() on each result).
When setting options, you often have a string read directly from the user. In such a case, simply passing it to av_opt_set() is enough. For non-string type options, av_opt_set() will parse the string according to the option type.
Similarly av_opt_get() will read any option type and convert it to a string which will be returned. Do not forget that the string is allocated, so you have to free it with av_free().
In some cases it may be more convenient to put all options into an AVDictionary and call av_opt_set_dict() on it. A specific case of this are the format/codec open functions in lavf/lavc which take a dictionary filled with option as a parameter. This allows to set some options that cannot be set otherwise, since e.g. the input file format is not known before the file is actually opened.
#define AV_OPT_SEARCH_CHILDREN 0x0001 |
Search in possible children of the given object first.
Definition at line 447 of file opt.h.
Referenced by av_opt_find2(), ff_rtp_chain_mux_open(), and opt_default().
#define AV_OPT_SEARCH_FAKE_OBJ 0x0002 |
The obj passed to av_opt_find() is fake – only a double pointer to AVClass instead of a required pointer to a struct containing AVClass.
This is useful for searching for options without needing to allocate the corresponding object.
Definition at line 455 of file opt.h.
Referenced by av_opt_find2(), filter_codec_opts(), and opt_default().
enum AVOptionType |
attribute_deprecated const AVOption* av_find_opt | ( | void * | obj, |
const char * | name, | ||
const char * | unit, | ||
int | mask, | ||
int | flags | ||
) |
Look for an option in obj.
Look only for the options which have the flags set as specified in mask and flags (that is, for which it is the case that opt->flags & mask == flags).
[in] | obj | a pointer to a struct whose first element is a pointer to an AVClass |
[in] | name | the name of the option to look for |
[in] | unit | the unit of the option to look for, or any if NULL |
attribute_deprecated double av_get_double | ( | void * | obj, |
const char * | name, | ||
const AVOption ** | o_out | ||
) |
attribute_deprecated int64_t av_get_int | ( | void * | obj, |
const char * | name, | ||
const AVOption ** | o_out | ||
) |
Definition at line 452 of file opt.c.
Referenced by new_output_stream(), and queue_picture().
attribute_deprecated AVRational av_get_q | ( | void * | obj, |
const char * | name, | ||
const AVOption ** | o_out | ||
) |
attribute_deprecated const char* av_get_string | ( | void * | obj, |
const char * | name, | ||
const AVOption ** | o_out, | ||
char * | buf, | ||
int | buf_len | ||
) |
attribute_deprecated const AVOption* av_next_option | ( | void * | obj, |
const AVOption * | last | ||
) |
Iterate over potential AVOptions-enabled children of parent.
prev | result of a previous call to this function or NULL |
Definition at line 797 of file opt.c.
Referenced by av_opt_find2(), and show_help_children().
Iterate over AVOptions-enabled children of obj.
prev | result of a previous call to this function or NULL |
Definition at line 789 of file opt.c.
Referenced by av_opt_find2().
const AVOption* av_opt_find | ( | void * | obj, |
const char * | name, | ||
const char * | unit, | ||
int | opt_flags, | ||
int | search_flags | ||
) |
Look for an option in an object.
Consider only options which have all the specified flags set.
[in] | obj | A pointer to a struct whose first element is a pointer to an AVClass. Alternatively a double pointer to an AVClass, if AV_OPT_SEARCH_FAKE_OBJ search flag is set. |
[in] | name | The name of the option to look for. |
[in] | unit | When searching for named constants, name of the unit it belongs to. |
opt_flags | Find only options with all the specified flags set (AV_OPT_FLAG). | |
search_flags | A combination of AV_OPT_SEARCH_*. |
Definition at line 747 of file opt.c.
Referenced by av_get_string(), av_opt_flag_is_set(), av_set_double(), av_set_int(), av_set_q(), av_set_string3(), avserver_opt_default(), filter_codec_opts(), opt_default(), and set_string_number().
const AVOption* av_opt_find2 | ( | void * | obj, |
const char * | name, | ||
const char * | unit, | ||
int | opt_flags, | ||
int | search_flags, | ||
void ** | target_obj | ||
) |
Look for an option in an object.
Consider only options which have all the specified flags set.
[in] | obj | A pointer to a struct whose first element is a pointer to an AVClass. Alternatively a double pointer to an AVClass, if AV_OPT_SEARCH_FAKE_OBJ search flag is set. |
[in] | name | The name of the option to look for. |
[in] | unit | When searching for named constants, name of the unit it belongs to. |
opt_flags | Find only options with all the specified flags set (AV_OPT_FLAG). | |
search_flags | A combination of AV_OPT_SEARCH_*. | |
[out] | target_obj | if non-NULL, an object to which the option belongs will be written here. It may be different from obj if AV_OPT_SEARCH_CHILDREN is present in search_flags. This parameter is ignored if search_flags contain AV_OPT_SEARCH_FAKE_OBJ. |
Definition at line 753 of file opt.c.
Referenced by av_opt_find(), av_opt_find2(), av_opt_get(), av_opt_set(), get_number(), and set_number().
int av_opt_flag_is_set | ( | void * | obj, |
const char * | field_name, | ||
const char * | flag_name | ||
) |
Check whether a particular flag is set in a flags field.
field_name | the name of the flag field option |
flag_name | the name of the flag to check |
Free all string and binary options in obj.
Definition at line 718 of file opt.c.
Referenced by av_write_trailer(), avcodec_close(), avformat_free_context(), ffurl_close(), and segment_end().
Iterate over all AVOptions belonging to obj.
obj | an AVOptions-enabled struct or a double pointer to an AVClass describing it. |
prev | result of the previous call to av_opt_next() on this object or NULL |
Definition at line 57 of file opt.c.
Referenced by av_next_option(), av_opt_find2(), av_opt_free(), av_opt_set_defaults2(), and opt_list().
Set the values of all AVOption fields to their default values.
s | an AVOption-enabled struct (its first member must be a pointer to AVClass) |
Definition at line 598 of file opt.c.
Referenced by avcodec_get_context_defaults3(), avcodec_open2(), avformat_get_context_defaults(), avformat_open_input(), avformat_write_header(), init(), init_common(), segment_start(), sws_alloc_context(), and url_alloc_for_protocol().
attribute_deprecated void av_opt_set_defaults2 | ( | void * | s, |
int | mask, | ||
int | flags | ||
) |
Definition at line 604 of file opt.c.
Referenced by av_opt_set_defaults().
int av_opt_set_dict | ( | void * | obj, |
struct AVDictionary ** | options | ||
) |
Definition at line 726 of file opt.c.
Referenced by avcodec_open2(), avformat_open_input(), avformat_write_header(), and ffurl_open().
Show the obj options.
req_flags | requested flags for the options to show. Show only the options for which it is opt->flags & req_flags. |
rej_flags | rejected flags for the options to show. Show only the options for which it is !(opt->flags & req_flags). |
av_log_obj | log context to use for showing the options |
Definition at line 586 of file opt.c.
Referenced by show_help(), and show_help_children().
attribute_deprecated const AVOption* av_set_double | ( | void * | obj, |
const char * | name, | ||
double | n | ||
) |
attribute_deprecated const AVOption* av_set_int | ( | void * | obj, |
const char * | name, | ||
int64_t | n | ||
) |
int av_set_options_string | ( | void * | ctx, |
const char * | opts, | ||
const char * | key_val_sep, | ||
const char * | pairs_sep | ||
) |
Parse the key/value pairs list in opts.
For each key/value pair found, stores the value in the field in ctx that is named like the key. ctx must be an AVClass context, storing is done using AVOptions.
key_val_sep | a 0-terminated list of characters used to separate key from value |
pairs_sep | a 0-terminated list of characters used to separate two pairs from each other |
Definition at line 698 of file opt.c.
Referenced by init(), and init_common().
attribute_deprecated const AVOption* av_set_q | ( | void * | obj, |
const char * | name, | ||
AVRational | n | ||
) |
attribute_deprecated int av_set_string3 | ( | void * | obj, |
const char * | name, | ||
const char * | val, | ||
int | alloc, | ||
const AVOption ** | o_out | ||
) |
Set the field of obj with the given name to value.
[in] | obj | A struct whose first element is a pointer to an AVClass. |
[in] | name | the name of the field to set |
[in] | val | The value to set. If the field is not of a string type, then the given string is parsed. SI postfixes and some named scalars are supported. If the field is of a numeric type, it has to be a numeric or named scalar. Behavior with more than one scalar and +- infix operators is undefined. If the field is of a flags type, it has to be a sequence of numeric scalars or named flags separated by '+' or '-'. Prefixing a flag with '+' causes it to be set without affecting the other flags; similarly, '-' unsets a flag. |
[out] | o_out | if non-NULL put here a pointer to the AVOption found |
alloc | this parameter is currently ignored |