函数 av_frame_alloc 

pub unsafe extern "C" fn av_frame_alloc() -> *mut AVFrame

Allocate an AVFrame and set its fields to default values. The resulting struct must be freed using av_frame_free().

@return An AVFrame filled with default values or NULL on failure.

@note this only allocates the AVFrame itself, not the data buffers. Those must be allocated through other means, e.g. with av_frame_get_buffer() or manually.