Replaces length memory blocks in buffer starting at idx with mem. If length is -1, all memory starting from idx will be removed and replaced with mem. buffer should be writable.
an index
a length should not be 0
a GstMemory. [transfer full]
See Implementation
Replaces length memory blocks in buffer starting at idx with mem. If length is -1, all memory starting from idx will be removed and replaced with mem. buffer should be writable.