RFE: h264 tune options configurable

[bugsyb]

Would it be possible please to pass to h264 additional options/parameters, even if without validation?
Key element is to be able to tune settings as below and potentially more:
[libx264 @ 0000000002167100] Possible tunes: film animation grain stillimage psnr ssim
fastdecode zerolatency

[mpromonet]

Hi,

Yes, sure, fill free to improve what you need.

Best Regards,
Michel.