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作者：罗上文，微信：Loken1，公众号：FFmpeg弦外之音

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DRM (Direct Rendering Manager)是Linux负责与现代GPU视频卡交互的内核⼦系统，

https://www.showapi.com/news/article/67079acb4ddd79f11a3bec29

你要讲一下这个 hwupload filter ，他主要是把 CPU 内存 移动到 GPU 内存。hwdownload filter 也要重点讲一下。

The encoders only accept input as VAAPI surfaces. If the input is in normal memory, it will need to be uploaded before giving the frames to the encoder - in the ffmpeg utility, the hwupload filter can be used for this. It will upload to a surface with the same layout as the software frame, so it may be necessary to add a format filter immediately before to get the input into the right format (hardware generally wants the nv12 layout, but most software functions use the yuv420p layout). The hwupload filter also requires a device to upload to, which needs to be defined before the filter graph is created.

CRF 为什么比 CQP 对于屏幕内容的压缩更有效？底层原理是什么？后面你写编解码原理的时候需要讲这块。

No CRF-like mode is currently supported. The only constant-quality mode is CQP (constant quantisation parameter), which has no adaptivity to scene content. It does, however, allow different quality settings for different frame types, to improve compression by spending fewer bits on unreferenced B-frames - see the (i|b)_q(factor|offset) options. CQP mode cannot be combined with a maximum bitrate or buffer size.