/**
* Get a metadata element with matching key.
+ *
* @param prev Set to the previous matching element to find the next.
* If set to NULL the first matching element is returned.
* @param flags Allows case as well as suffix-insensitive comparisons.
#if LIBAVFORMAT_VERSION_MAJOR == 52
/**
* Set the given tag in m, overwriting an existing tag.
+ *
* @param key tag key to add to m (will be av_strduped)
* @param value tag value to add to m (will be av_strduped)
* @return >= 0 on success otherwise an error code <0
/**
* Set the given tag in m, overwriting an existing tag.
+ *
* @param key tag key to add to m (will be av_strduped depending on flags)
* @param value tag value to add to m (will be av_strduped depending on flags).
* Passing a NULL value will cause an existing tag to be deleted.
* Convert all the metadata sets from ctx according to the source and
* destination conversion tables. If one of the tables is NULL, then
* tags are converted to/from ffmpeg generic tag names.
+ *
* @param d_conv destination tags format conversion table
* @param s_conv source tags format conversion table
*/