I often see ARM-based chips advertising onboard GPUs, like the RPI3 that came with "Broadcom VideoCore IV @ 250 MHz" and the OdroidC2 that comes with a "Mali-450 GPU". These chips advertise stuff like "Decode 4k/30FPS, Encode 1080p,30FPS" as the capabilities of the GPU for encoding and decoding videos.
My question is this - how does a program like Kodi, VLC, or FFMPEG come to make use of these GPUs for actual encoding and decoding? When I do research on how to make use of the Mali-450 GPU, for example, I find some esoteric and poorly documented C-examples of sending compressed frames to the GPU and getting decoded frames back. If I were to use a device like the OdroidC2 and install VLC on it, how does VLC make use of the GPU? Did someone have to write logic into VLC to use the specific encoding/decoding API exposed by the Mali GPU in order to use it or do these GPUs follow some sort of consistent API that is exposed by all GPUs and VLC/Kodi can just program against this system API?
The reason I ask this question is that VLC and Kodi tend to support these GPUs out of the Box, but a very popular program like FFMPEG that prides itself on supporting as many codecs and accelerators as possible has no support for decoding and encoding with the Mali GPU series. Why would VLC/Kodi support encoding/decoding and not FFMPEG? Why do these manufacturers claim wild decoding and encoding support if these GPUs are difficult to program against and one must use their custom esoteric APIs instead of something like libavcodec?
I hope my question makes sense, I guess what I'm curious about is that GPUs on most systems whether it be the Intel HD Graphics, Nvidia cards, AMD cards, etc seem to be used automatically by most video players but when it comes to using something like FFMPEG against these devices the process becomes much more process and you need to custom compile the build and give special flags to use the device as intended. Is there something I'm missing here? Is VLC programmed to make use of all of these different type of GPUs? And why, in that case, does FFMEPG not support Mali GPUs out of the Box?
