Fix subtitle encoder if webvtt is requested

[sleepycatcoding]

Changes
Properly convert subtitles to webvtt if requested.

Issues
Fixes jellyfin/jellyfin-android#1028

[nielsvanvelzen]

The app is requesting the wrong URL. The extension for WebVTT is .vtt and the app is requesting .webvtt. So IMO this is not a bug in the server.

[sleepycatcoding]

Isn't then requesting .subrip also a bug in the app?

[sleepycatcoding]

The app is requesting the wrong URL. The extension for WebVTT is .vtt and the app is requesting .webvtt. So IMO this is not a bug in the server.

This is a bug in the server, because the app uses the deliveryUrl from the server that is already wrong.

The URL is generated here:

jellyfin/MediaBrowser.Model/Dlna/StreamInfo.cs

Lines 894 to 902 in 6e14f26

	info.Url = string.Format(
	CultureInfo.InvariantCulture,
	"{0}/Videos/{1}/{2}/Subtitles/{3}/{4}/Stream.{5}",
	baseUrl,
	ItemId,
	MediaSourceId,
	stream.Index.ToString(CultureInfo.InvariantCulture),
	startPositionTicks.ToString(CultureInfo.InvariantCulture),
	subtitleProfile.Format);

Later set as deliveryUrl here:

jellyfin/Jellyfin.Api/Helpers/MediaInfoHelper.cs

Lines 466 to 470 in 6e14f26

	if (profile.DeliveryMethod == SubtitleDeliveryMethod.External)
	{
	stream.DeliveryUrl = profile.Url.TrimStart('-');
	stream.IsExternalUrl = profile.IsExternalUrl;
	}

The subtitleProfile.Format is webvtt. A better fix probably would be to use file extensions instead of format in the URL.

[jellyfin-bot]

This pull request has merge conflicts. Please resolve the conflicts so the PR can be successfully reviewed and merged.

[jellyfin-bot]

This pull request has merge conflicts. Please resolve the conflicts so the PR can be successfully reviewed and merged.

[aseering]

I'm running into this as well. Is the patch in need of any tweaks or further changes? Happy to help.