[ffmpeg] av_opt_set 解析
2023-12-13 04:04:19
背景
ffmpeg 创建编码器的时候,可以设置一些额外参数。可以通过两种方式,一是 av_opt_set,另一种是 avcodec_open2 最后一个参数传入。今天先分析一下第一种是什么设置进去的。
具体代码分析
av_opt_set 主要分成两部分,一个是在 obj 结构体中,找到 name 的地址。第二个是根据找到地址的类型, 解析 val,并将 val 赋值到该地址。
int av_opt_set(void *obj, const char *name, const char *val, int search_flags)
{
int ret = 0;
void *dst, *target_obj;
const AVOption *o = av_opt_find2(obj, name, NULL, 0, search_flags, &target_obj);
if (!o || !target_obj)
return AVERROR_OPTION_NOT_FOUND;
FF_DISABLE_DEPRECATION_WARNINGS
if (!val && (o->type != AV_OPT_TYPE_STRING &&
o->type != AV_OPT_TYPE_PIXEL_FMT && o->type != AV_OPT_TYPE_SAMPLE_FMT &&
o->type != AV_OPT_TYPE_IMAGE_SIZE &&
o->type != AV_OPT_TYPE_DURATION && o->type != AV_OPT_TYPE_COLOR &&
#if FF_API_OLD_CHANNEL_LAYOUT
o->type != AV_OPT_TYPE_CHANNEL_LAYOUT &&
#endif
o->type != AV_OPT_TYPE_BOOL))
return AVERROR(EINVAL);
FF_ENABLE_DEPRECATION_WARNINGS
if (o->flags & AV_OPT_FLAG_READONLY)
return AVERROR(EINVAL);
if (o->flags & AV_OPT_FLAG_DEPRECATED)
av_log(obj, AV_LOG_WARNING, "The \"%s\" option is deprecated: %s\n", name, o->help);
dst = ((uint8_t *)target_obj) + o->offset;
switch (o->type) {
case AV_OPT_TYPE_BOOL:
return set_string_bool(obj, o, val, dst);
case AV_OPT_TYPE_STRING:
return set_string(obj, o, val, dst);
case AV_OPT_TYPE_BINARY:
return set_string_binary(obj, o, val, dst);
case AV_OPT_TYPE_FLAGS:
case AV_OPT_TYPE_INT:
case AV_OPT_TYPE_INT64:
case AV_OPT_TYPE_UINT64:
case AV_OPT_TYPE_FLOAT:
case AV_OPT_TYPE_DOUBLE:
case AV_OPT_TYPE_RATIONAL:
return set_string_number(obj, target_obj, o, val, dst);
case AV_OPT_TYPE_IMAGE_SIZE:
return set_string_image_size(obj, o, val, dst);
case AV_OPT_TYPE_VIDEO_RATE: {
AVRational tmp;
ret = set_string_video_rate(obj, o, val, &tmp);
if (ret < 0)
return ret;
return write_number(obj, o, dst, 1, tmp.den, tmp.num);
}
case AV_OPT_TYPE_PIXEL_FMT:
return set_string_pixel_fmt(obj, o, val, dst);
case AV_OPT_TYPE_SAMPLE_FMT:
return set_string_sample_fmt(obj, o, val, dst);
case AV_OPT_TYPE_DURATION:
{
int64_t usecs = 0;
if (val) {
if ((ret = av_parse_time(&usecs, val, 1)) < 0) {
av_log(obj, AV_LOG_ERROR, "Unable to parse option value \"%s\" as duration\n", val);
return ret;
}
}
if (usecs < o->min || usecs > o->max) {
av_log(obj, AV_LOG_ERROR, "Value %f for parameter '%s' out of range [%g - %g]\n",
usecs / 1000000.0, o->name, o->min / 1000000.0, o->max / 1000000.0);
return AVERROR(ERANGE);
}
*(int64_t *)dst = usecs;
return 0;
}
case AV_OPT_TYPE_COLOR:
return set_string_color(obj, o, val, dst);
#if FF_API_OLD_CHANNEL_LAYOUT
FF_DISABLE_DEPRECATION_WARNINGS
case AV_OPT_TYPE_CHANNEL_LAYOUT:
if (!val || !strcmp(val, "none")) {
*(int64_t *)dst = 0;
} else {
int64_t cl = av_get_channel_layout(val);
if (!cl) {
av_log(obj, AV_LOG_ERROR, "Unable to parse option value \"%s\" as channel layout\n", val);
ret = AVERROR(EINVAL);
}
*(int64_t *)dst = cl;
return ret;
}
break;
FF_ENABLE_DEPRECATION_WARNINGS
#endif
case AV_OPT_TYPE_CHLAYOUT:
ret = set_string_channel_layout(obj, o, val, dst);
if (ret < 0) {
av_log(obj, AV_LOG_ERROR, "Unable to parse option value \"%s\" as channel layout\n", val);
ret = AVERROR(EINVAL);
}
return ret;
case AV_OPT_TYPE_DICT:
return set_string_dict(obj, o, val, dst);
}
av_log(obj, AV_LOG_ERROR, "Invalid option type.\n");
return AVERROR(EINVAL);
}
找到 name 的地址
主要关注 av_opt_next 函数,第一次进去返回 option 地址,之后进去每次往后移动一个 option。并将获得的 option name 与传入的 name 进行比较。
const AVOption *av_opt_find2(void *obj, const char *name, const char *unit,
int opt_flags, int search_flags, void **target_obj)
{
const AVClass *c;
const AVOption *o = NULL;
if(!obj)
return NULL;
c= *(AVClass**)obj;
if (!c)
return NULL;
// 非必要,先不看
if (search_flags & AV_OPT_SEARCH_CHILDREN) {
if (search_flags & AV_OPT_SEARCH_FAKE_OBJ) {
void *iter = NULL;
const AVClass *child;
while (child = av_opt_child_class_iterate(c, &iter))
if (o = av_opt_find2(&child, name, unit, opt_flags, search_flags, NULL))
return o;
} else {
void *child = NULL;
while (child = av_opt_child_next(obj, child))
if (o = av_opt_find2(child, name, unit, opt_flags, search_flags, target_obj))
return o;
}
}
while (o = av_opt_next(obj, o)) {
if (!strcmp(o->name, name) && (o->flags & opt_flags) == opt_flags &&
((!unit && o->type != AV_OPT_TYPE_CONST) ||
(unit && o->type == AV_OPT_TYPE_CONST && o->unit && !strcmp(o->unit, unit)))) {
if (target_obj) {
if (!(search_flags & AV_OPT_SEARCH_FAKE_OBJ))
*target_obj = obj;
else
*target_obj = NULL;
}
return o;
}
}
return NULL;
}
const AVOption *av_opt_next(const void *obj, const AVOption *last)
{
const AVClass *class;
if (!obj)
return NULL;
class = *(const AVClass**)obj;
if (!last && class && class->option && class->option[0].name)
return class->option;
if (last && last[1].name)
return ++last;
return NULL;
}
以 aacenc.c 中的 aacenc_options 进行分析,可以注意到最后一个 option 是 NULL,和codec_list 一样的手法。
static const AVOption aacenc_options[] = {
{"aac_coder", "Coding algorithm", offsetof(AACEncContext, options.coder), AV_OPT_TYPE_INT, {.i64 = AAC_CODER_TWOLOOP}, 0, AAC_CODER_NB-1, AACENC_FLAGS, "coder"},
{"anmr", "ANMR method", 0, AV_OPT_TYPE_CONST, {.i64 = AAC_CODER_ANMR}, INT_MIN, INT_MAX, AACENC_FLAGS, "coder"},
{"twoloop", "Two loop searching method", 0, AV_OPT_TYPE_CONST, {.i64 = AAC_CODER_TWOLOOP}, INT_MIN, INT_MAX, AACENC_FLAGS, "coder"},
{"fast", "Default fast search", 0, AV_OPT_TYPE_CONST, {.i64 = AAC_CODER_FAST}, INT_MIN, INT_MAX, AACENC_FLAGS, "coder"},
{"aac_ms", "Force M/S stereo coding", offsetof(AACEncContext, options.mid_side), AV_OPT_TYPE_BOOL, {.i64 = -1}, -1, 1, AACENC_FLAGS},
{"aac_is", "Intensity stereo coding", offsetof(AACEncContext, options.intensity_stereo), AV_OPT_TYPE_BOOL, {.i64 = 1}, -1, 1, AACENC_FLAGS},
{"aac_pns", "Perceptual noise substitution", offsetof(AACEncContext, options.pns), AV_OPT_TYPE_BOOL, {.i64 = 1}, -1, 1, AACENC_FLAGS},
{"aac_tns", "Temporal noise shaping", offsetof(AACEncContext, options.tns), AV_OPT_TYPE_BOOL, {.i64 = 1}, -1, 1, AACENC_FLAGS},
{"aac_ltp", "Long term prediction", offsetof(AACEncContext, options.ltp), AV_OPT_TYPE_BOOL, {.i64 = 0}, -1, 1, AACENC_FLAGS},
{"aac_pred", "AAC-Main prediction", offsetof(AACEncContext, options.pred), AV_OPT_TYPE_BOOL, {.i64 = 0}, -1, 1, AACENC_FLAGS},
{"aac_pce", "Forces the use of PCEs", offsetof(AACEncContext, options.pce), AV_OPT_TYPE_BOOL, {.i64 = 0}, -1, 1, AACENC_FLAGS},
FF_AAC_PROFILE_OPTS
{NULL}
};
typedef struct AVOption {
const char *name;
/**
* short English help text
* @todo What about other languages?
*/
const char *help;
/**
* The offset relative to the context structure where the option
* value is stored. It should be 0 for named constants.
*/
int offset;
enum AVOptionType type;
/**
* the default value for scalar options
*/
union {
int64_t i64;
double dbl;
const char *str;
/* TODO those are unused now */
AVRational q;
} default_val;
double min; ///< minimum valid value for the option
double max; ///< maximum valid value for the option
int flags;
#define AV_OPT_FLAG_ENCODING_PARAM 1 ///< a generic parameter which can be set by the user for muxing or encoding
#define AV_OPT_FLAG_DECODING_PARAM 2 ///< a generic parameter which can be set by the user for demuxing or decoding
#define AV_OPT_FLAG_AUDIO_PARAM 8
#define AV_OPT_FLAG_VIDEO_PARAM 16
#define AV_OPT_FLAG_SUBTITLE_PARAM 32
/**
* The option is intended for exporting values to the caller.
*/
#define AV_OPT_FLAG_EXPORT 64
/**
* The option may not be set through the AVOptions API, only read.
* This flag only makes sense when AV_OPT_FLAG_EXPORT is also set.
*/
#define AV_OPT_FLAG_READONLY 128
#define AV_OPT_FLAG_BSF_PARAM (1<<8) ///< a generic parameter which can be set by the user for bit stream filtering
#define AV_OPT_FLAG_RUNTIME_PARAM (1<<15) ///< a generic parameter which can be set by the user at runtime
#define AV_OPT_FLAG_FILTERING_PARAM (1<<16) ///< a generic parameter which can be set by the user for filtering
#define AV_OPT_FLAG_DEPRECATED (1<<17) ///< set if option is deprecated, users should refer to AVOption.help text for more information
#define AV_OPT_FLAG_CHILD_CONSTS (1<<18) ///< set if option constants can also reside in child objects
//FIXME think about enc-audio, ... style flags
/**
* The logical unit to which the option belongs. Non-constant
* options and corresponding named constants share the same
* unit. May be NULL.
*/
const char *unit;
} AVOption;
根据找到地址的类型, 解析 val,并将 val 赋值到该地址
以 set_string_bool 举例。可以看见如果传入 auto,则会赋值 -1;true,y,yes,enable,enabled,on 赋值 1,false,n,no,disable,disabled,off 为0。
其他类型的赋值,大家可以去看具体的函数。
static int set_string_bool(void *obj, const AVOption *o, const char *val, int *dst)
{
int n;
if (!val)
return 0;
if (!strcmp(val, "auto")) {
n = -1;
} else if (av_match_name(val, "true,y,yes,enable,enabled,on")) {
n = 1;
} else if (av_match_name(val, "false,n,no,disable,disabled,off")) {
n = 0;
} else {
char *end = NULL;
n = strtol(val, &end, 10);
if (val + strlen(val) != end)
goto fail;
}
if (n < o->min || n > o->max)
goto fail;
*dst = n;
return 0;
fail:
av_log(obj, AV_LOG_ERROR, "Unable to parse option value \"%s\" as boolean\n", val);
return AVERROR(EINVAL);
}
寻找地址
target_obj 就是 av_opt_set 传入的地址, offset 是每个 option,在编码器结构体中的偏移量。 offsetof(AACEncContext, options.coder)
dst = ((uint8_t *)target_obj) + o->offset;
#define offsetof(s,m) ((size_t)&(((s*)0)->m))
文章来源:https://blog.csdn.net/dss875914213/article/details/134840341
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本文来自互联网用户投稿,该文观点仅代表作者本人,不代表本站立场。本站仅提供信息存储空间服务,不拥有所有权,不承担相关法律责任。 如若内容造成侵权/违法违规/事实不符,请联系我的编程经验分享网邮箱:veading@qq.com进行投诉反馈,一经查实,立即删除!