函数 av_hwdevice_ctx_alloc 

pub unsafe extern "C" fn av_hwdevice_ctx_alloc(
    type_: AVHWDeviceType,
) -> *mut AVBufferRef

Allocate an AVHWDeviceContext for a given hardware type.

@param type the type of the hardware device to allocate. @return a reference to the newly created AVHWDeviceContext on success or NULL on failure.