public void registerRtFrameCallback(@NonNull FrameDrawingCallback callback) {
    if (mAttachInfo.mThreadedRenderer != null) {
        mAttachInfo.mThreadedRenderer.registerRtFrameCallback(frame -> {
            try {
                callback.onFrameDraw(frame);
            } catch (Exception e) {
                Log.e(TAG, "Exception while executing onFrameDraw", e);
            }
        });
    }
}

调用 ThreadedRenderer.registerRtFrameCallback() 注册 callback，在下一帧到来时回调。