Created Archive (markdown)

Archive.md

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+# What?
+
+youtube-dl's [archive](https://github.com/ytdl-org/youtube-dl/blob/master/README.md#how-do-i-download-only-new-videos-from-a-playlist) feature allows you to skip downloading already-downloaded videos.
+
+We use the `--download-archive <archive path>` arg, where we modify <archive path> depending on how the video is being downloaded. We keep separate archives because different users shouldn't use the same archive (otherwise they could not download the same video).
+
+The following table summarizes where we store the archive:
+
+|                       | Single-user mode                  | Multi-user mode                                    |
+|-----------------------|-----------------------------------|----------------------------------------------------|
+| **One-off download**      | appdata/archives                  | users/\<username>/archives                          |
+| **Subscription download** | subscriptions/archives/\<sub name> | users/\<username>/subscriptions/archives/\<sub name> |
+
+In each folder you can find 3 types of text files:
+* archive_\<type>.txt
+  * Running list of downloaded files
+* blacklist_\<type>.txt
+  * "Blacklisted" videos go here, where they are removed from the archive_\<type>.txt but inserted into here. This allows you to keep a clean archive but still avoid redownloading a video (most useful for subscriptions)
+* merged_\<type>.txt
+  * This file is autogenerated, and simply a combination of the archive and blacklist
+
+# Why?
+
+There's a few reasons why you may want to use the archive.
+
+If you delete a subscription video without archiving functionality, that video will be downloaded again as long as that video is within the time scope of the subscription.
+
+This may also be useful if you primarily use YoutubeDL-Material as a downloader rather than a library.