Enhancement: templates and better filter support for #raw

[chatziko]

#raw is super useful, but currently has 2 limitations

• no template support
• cannot use -vf in cases when go2rtc adds its own filters (ffmpeg only accepts a single -vf)

So I propose the following:

1. Add template support: #raw=my_template should be expanded if a template my_template exists.
2. If raw (after expansion) contains -vf then go2rtc should not insert its own filters, it's the user's responsibility to add all filters in the proper order.

A possible use case is #402, but I can imagine many others, raw/filters are very general features.

[AlexxIT]

#filter=value also good idea

[chatziko]

#filter=value also good idea

Indeed, in fact I started writing this issue after my comment in #402 to suggest #filter=value.

But then I realized a problem: in what order should the user filters be combined with the generated ones? Say #hardware adds hwupload, I might want to add a filter either before or after. So maybe its easier to let the user supply all filters without merging, in which case #raw is already sufficient, no need to introduce #filter.

[AlexxIT]

https://github.com/AlexxIT/go2rtc/releases/tag/v1.6.0

[AlexxIT]

I made support for software filters + hardware encoding. Hopefully this solves the problem mentioned.