Pitivi's Proxy Preparation Procedure

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Internally, most of the code for handling proxies resides in proxy.py which exposes the proxy_manager class to create and monitor proxy assets.

To create a proxy, we call add_job function in proxy_manager which takes the GES.Asset that we wish to proxy as its argument, performs some checks and passes it on to another function.

This function is now responsible for getting the suitable EncodingProfile and starting off a GstTranscoder on the asset with this profile as its target format.

The transcoder runs asynchronously, reporting progress periodically which is used to update the UI in the Media Library.

When the transcoder finishes, we GES.request_async the resulting proxy file and set it as the proxy on the original asset.

The modifications required for the generation of scaled proxies are fairly straightforward, just set_restriction on the EncodingProfile telling it the height and width that we wish to scale the asset to and let GstTranscoder work its wonders.

The complications lie mostly in adapting the current framework that is used for initiating proxy creation, managing proxies during their lifecycle and handling of edge cases like poorly supported the formats or the changing of the target resolution for scaled proxies mid-way through.