Add full Raspberry Pi hardware accelerated decoding support

[ferferga]

Although support to the Broadcom Multimedia Abstraction Layer has been added to jellyfin-ffmpeg and h264_mmal was already handled in the logic of the server, it seems that it wasn't registered as a valid one in the validator and it's simply skipped.

This quick PR aims to add full support for all the hardware accelerated codecs that the Pi and MMAL-capable devices provides. Although it can be instantly merged, it should be considered as a WIP, as I'm still testing in my environment all the filetypes and bitrates possible.

[JustAMan]

Looks good.

[JustAMan]

@ferferga I noted that your PR title says "decoding support" but you were actually adding encoders, so I tweaked the title. Please check I did so correctly.

[ferferga]

@JustAMan Hmm, that's not what I meant to do then, as mmal is a HW decoder only (OMX is the encoder in Pi's case).

I added the missing decoders to the GetHardwareAcceleratedVideoDecoder and requiredDecoders strings, just in line where other HW decoders are. Although the EncodingHelper and EncodingValidator names are a bit misleading, it seems to me that it's where all the logic for both decoding and encoding happens.

Correct me if I'm wrong, because otherwise I'm completely implementing this the other way around.

[JustAMan]

Hmm, I read the code better and I now think you're indeed specifying a decoder.
I just never saw before that -codec could be used to specify a decoder. Excuse me, I "fixed" the title back.

[ferferga]

@JustAMan No problem! 😁👍