* dumping/ffmpeg_backend: Add FPS filter
So that the recorded video can be at 60FPS (which is supported by most encoders) while still maintaining correct speed.
* dumping/ffmpeg_backend: Add HW context support
Required for some HW acceled encoders. Not tested as my devices don't seem to require this.
* CMake: Copy avfilter dll for MSVC
* CMakeLists: Require FFmpeg 4.0
* ffmpeg: Fix dumper compile error on MSVC.
* ffmpeg: Address review comments.
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Co-authored-by: zhupengfei <zhupf321@gmail.com>
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