十三、GstTagList
1 GstTagList基本概念
-
用于描述媒体metadata元数据的标签tag和值value的列表。
-
结构中的字符串必须是ASCII或UTF-8编码。不允许使用其他编码。字符串不得为空或为%NULL。
2 GstTagList类型结构
2.1 GstTagList类型注册宏定义
/* filename: gsttaglist.h */
GST_API GType _gst_tag_list_type;
#define GST_TYPE_TAG_LIST (_gst_tag_list_type)
/* filename: gsttaglist.c */
GType _gst_tag_list_type = 0;
GST_DEFINE_MINI_OBJECT_TYPE (GstTagList, gst_tag_list);
2.2 GstTagList类型相关枚举
2.2.1 GstTagMergeMode
/* filename: gsttaglist.h */
/**
* GstTagMergeMode:
* @GST_TAG_MERGE_UNDEFINED: undefined merge mode
* @GST_TAG_MERGE_REPLACE_ALL: replace all tags (clear list and append)
* @GST_TAG_MERGE_REPLACE: replace tags
* @GST_TAG_MERGE_APPEND: append tags
* @GST_TAG_MERGE_PREPEND: prepend tags
* @GST_TAG_MERGE_KEEP: keep existing tags
* @GST_TAG_MERGE_KEEP_ALL: keep all existing tags
* @GST_TAG_MERGE_COUNT: the number of merge modes
*
* 不同的标签合并模式基本上有替换、覆盖和追加，但可以从两个方向看待。
* 考虑到两个标签列表：(A)元素中已经存在的标签和(B)提供给元素的标签
* 例如，通过gst_tag_setter_merge_tags() / gst_tag_setter_add_tags()或%GST_EVENT_TAG），这些标签如何合并？
* 在下表中，显示了标签存在于列表(A)或不存在于列表(!A)以及它们的组合情况。
*
* | merge mode | A + B | A + !B | !A + B | !A + !B |
* | ----------- | ----- | ------ | ------ | ------- |
* | REPLACE_ALL | B | ø | B | ø |
* | REPLACE | B | A | B | ø |
* | APPEND | A, B | A | B | ø |
* | PREPEND | B, A | A | B | ø |
* | KEEP | A | A | B | ø |
* | KEEP_ALL | A | A | ø | ø |
*/
typedef enum {
GST_TAG_MERGE_UNDEFINED,
GST_TAG_MERGE_REPLACE_ALL,
GST_TAG_MERGE_REPLACE,
GST_TAG_MERGE_APPEND,
GST_TAG_MERGE_PREPEND,
GST_TAG_MERGE_KEEP,
GST_TAG_MERGE_KEEP_ALL,
/* add more */
GST_TAG_MERGE_COUNT
} GstTagMergeMode;
2.2.2 GstTagFlag
/* filename: gsttaglist.h */
/**
* GstTagFlag:
* @GST_TAG_FLAG_UNDEFINED: undefined flag
* @GST_TAG_FLAG_META: tag is meta data
* @GST_TAG_FLAG_ENCODED: tag is encoded
* @GST_TAG_FLAG_DECODED: tag is decoded
* @GST_TAG_FLAG_COUNT: number of tag flags
*
* Extra tag flags used when registering tags.
*/
/* FIXME: these are not really flags .. */
typedef enum {
GST_TAG_FLAG_UNDEFINED,
GST_TAG_FLAG_META,
GST_TAG_FLAG_ENCODED,
GST_TAG_FLAG_DECODED,
GST_TAG_FLAG_COUNT
} GstTagFlag;
2.2.3 GstTagScope
/**
* GstTagScope:
* @GST_TAG_SCOPE_STREAM: tags被用于单一的流stream
* @GST_TAG_SCOPE_GLOBAL: global tags被用于完整的medium
*
* GstTagScope specifies if a taglist applies to the complete
* medium or only to one single stream.
*/
typedef enum {
GST_TAG_SCOPE_STREAM,
GST_TAG_SCOPE_GLOBAL
} GstTagScope;
2.3 GstTagList相关结构体
2.3.1 GstTagList
/* filename: gsttaglist.h */
typedef struct _GstTagList GstTagList;
struct _GstTagList {
GstMiniObject mini_object;
};
2.3.2 GstTagInfo
/* filename: gsttaglist.c */
typedef struct
{
GType type; /* type the data is in */
const gchar *nick; /* translated short description */
const gchar *blurb; /* translated long description */
GstTagMergeFunc merge_func; /* functions to merge the values */
GstTagFlag flag; /* type of tag */
GQuark name_quark; /* quark for the name */
}
GstTagInfo;
2.3.3 GstTagListImpl
/* filename: gsttaglist.c */
typedef struct _GstTagListImpl
{
GstTagList taglist;
GstStructure *structure;
GstTagScope scope;
} GstTagListImpl;