add other hardware support

[bmegli]

Adding other hardware support should be rather easy but this needs:

• using correct encoder
• using correct pixel format for hardware

This is simpler in FFmpeg 4.0 and later.

I don't really need this future so this is distant future (if ever)

[bmegli]

This was already implemented in HVD so just copy the relevant section(s) of code

[bmegli]

Some conclusions after quick implementation trial with FFmpeg:

• this is not so easy
• the situation is not symmetric to the one with decoders
• there are different levels of hardware acceleration api support in FFmpeg
  • what we use in HVD for vaapi, vdpau, dxva2, d3d11, videotoolbox is internal type
  • there is no internal support for encoders, there's only standalone

It seems that for the standalone encoders:

• you can't initialize hardware for particular codec like h264
• you have to use full codec+hardware like "h264_vaapi", "h264_nvenc" (mingled hardware and codec ready solution)

It is definitely doable in a clumsy hacky way with heuristics:

• concatenate the hardware and codec string
• try to find AVCodec by concatenated name
• have a pixel format association table for the hardware

I don't really like the above solution.

What I really need is VAAPI so this issue is put for later (if ever)

[bmegli]

Hack for anybody who needs other hardware.

Know your hardware and check what FFmpeg supports with

ffmpeg -codecs

Or grep by hardware type:

ffmpeg -codecs | grep vaapi
ffmpeg -codecs | grep nvenc
ffmpeg -codecs | grep omx
# ...

Identify the hardware codec you would like to use and:

• change the "h264_vaapi" in hve.c to your desired codec
• change the pixel format used for hardware (AV_PIX_FMT_VAAPI) to match your hardware
• try it out
• if it breaks fix it (e.g., adjust software pixel format to whatever you hardware accepts)

[bmegli]

You can get some idea which format to use with:

ffmpeg -pix_fmts

Look for the ones described with H - Hardware Accelerated Format

[bmegli]

After making encoder configurable in ac3a4c1 the only things holding support for other hardware seem to be:

• hw_device_context creation
• hardware pixel format

What I need is VAAPI, so I am not going to touch it right now.

If anybody needs other hardware support those are the lines to hack.

[bmegli]

In #32 library was generalized to support also Nvidia NVENC

Generalizing for more hardware should be even easier now.

[bmegli]

Generally Intel, AMD, Nvidia and Nvidia jetson work but may have their quirks

See:

• clarify Nvidia and ATI/AMD situation #15 (comment)