build_ffmpeg_proxies: auto-detect proxies to (not) build

[NathanLovato]

UPDATE:
The default location for proxies in Blender is:

• you get a BL_proxy folder that contains proxies next to your media
• Video proxies end in BL_proxy/%filename%/proxy_%size (25, 50, or 100)%.AVI: one folder for each video, with the same name as the original video file.
• Picture proxies are in `BL_proxy/images/%size (25, 50, or 100)%/%filename%

To detect new proxies that need to be built it's easy enough: you can check for missing paths.
For now we rarely need to update proxies as you're not going to change recorded footage... so I've updated the task to reflect that need.

[NathanLovato]

Work started on the ffmpeg-build-script branch. First refactoring and breaking down the script then I'll add the timestamps etc.

Where would you save the timestamps and build data? Inside each BL_proxy folder?

Note for later: it'd be nice to find someone who's really experienced with video encoding and ffmpeg in particular to improve the proxy rendering speed, playback speed for the generated footage...

[sudopluto]

i think we can break this up to two parts:

• 1. sort of static monitoring of file changes
• 2. the sort of watchdog service that is popular in web dev servers

[NathanLovato]

Watching would be nice, but yeah first things first: that would be for another task. I think it'd be best to integrate it as a Blender operator and connecting it to the built-in progress bar before adding something like watch.

[NathanLovato]

Can you take care of it @razcore-art ? I don't want BPSProxies to have support for all proxy options in Blender as it would make it impossible to use the tool outside of Blender and be more code to maintain.

[razcore-rad]

I'll close this and open up an issue to keep track of stuff to improve at the BPSProxy new repo