Download release that already have available subtitles

[yodapotatofly]

I open this discussion following that refused feature request #8275

The idea is to avoid being stuck with an episode that doesn't finds matching subtitles, resulting in an endless loop of postponing the post-processing. The original author @PrzemekSkw ask if it would be possible to first search for the subtitles, then search for a matching video release, but this as been judged not faisible because it would "hammer the subtitle sites".

@p0psicles explained to me over discord that

The frequency of searching for subs, is much lower then the freq of searches
like daily search every 20 min. (some 10). + backlog searches + potential manual/forced searches

subtitle sites already hate that apps like sickrage, sonarr, medusa scrape their sites. So if we exponentially increase the load. It's a matter of time before they will start using captcha or cloudflare

I understand that it is not that smart to simply search for subtitles first, as if they are not available yet, it keeps requesting for subtitles over and over, even before the video files are available.
Still, I found it kinda dumb to download a file without knowing if it will ever find subtitles.

As of today, when subtitles are requested for a show, we have one of the following behaviour :

1. Good thing, there are embbed subtitles in the required language, no subtitle search needed
2. There are no embbed subtitles in the required language, but subtitles matching the release are found on first try
3. There are no embbed subtitles in the required language, and no subtitles matching the release are found. -> Postponing the post processing and waiting for next subtitle search, defined by the Subtitle Find Frequency (default 1 hour)

In the best case, subtitle website are not hitted at all, but on the worst case, there are hitted indefinitely every 1 hour.
If we have multiple episodes with missing subtitles, this hits the website multiples times each hour.

First of all, it seems quite logic to me that we should verify the subtitles disponibility before downloading an episode.
Indeed, when for a given release, it is hard to tell wether or not subtitles will be available. On the other hand, for a given subtitle file, we can be sure that the matching episode release is available somewhere.

Moreover, priorityzing the search for subtitle over the search for the episode doesn't necessarly mean that we have to flood the subtitles website. We just have to find a clever way to do it.

One way of dealing with that would be to flag the video release in the search results with a label.
We would then start by checking files that have specific subtitle-keyword (VOST** , sub*****) and flaging them. If one is found that has the highest score (i.e. matching prefered quality and/or prefered keywords), then download it. Else, search for subtitles on the first provider and match the subtitle result with the video files. Flag each videofile that has a matching subtitle. Again, if the highest score video is flagged, then downloaded it, else re-iterate on next subtitle provider.
At the end, download the video that has the highest score among the flagged ones.
The flags should be saved and conserved from one search to another

If I selected this approch over a simple search for every espisode going down the score is because it allows to do only one generic search on each subtitle site instead of multiple specific search (one per release).

Therefore, in the worst case, each site is hitted only once at each search (so not more itensive than the actual behaviour)

If no release manage to get flagged by the end of the search (proably subs are not yet available), then postpone the search for the 1 hour (or whatever delay is set betwin subtitles search).

It might not be the better/ideal solution but it adresses the issue raised by @PrzemekSkw while not being more intensive on subtitles websites

Sorry for this massive post, I hope this will lead to a constructive discussion about the best way to implement such a feature