函数 av_buffersink_set_frame_size 

pub unsafe extern "C" fn av_buffersink_set_frame_size(
    ctx: *mut AVFilterContext,
    frame_size: c_uint,
)

Set the frame size for an audio buffer sink.

All calls to av_buffersink_get_buffer_ref will return a buffer with exactly the specified number of samples, or AVERROR(EAGAIN) if there is not enough. The last buffer at EOF will be padded with 0.