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I've stumbled across a few YouTube video lists in the past which were supposed to have soundtracks to a game or a movie but somehow had random videos in-between expected videos (only a few were like that). I wonder if it was a mistake or intentional, or if those videos (being soundtracks) got taken down and after several years were reassigned to new videos. Does YouTube ever reuse video IDs/urls?

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No, I don't think YouTube ever reassigns old video IDs.

YouTube isn't running out of video URLs any time soon. In his video Will YouTube Ever Run Out Of Video IDs?, Tom Scott calculated that YouTube could generate over 73 quintillion video URLs. For reference, that's 73,786,976,294,838,206,4641 unique possibilies.

So while it's theoretically possible that YouTube is reusing video URLs, it is highly unlikely. Mainly because they don't have any reason to reuse old URLs.

1The number of unique URLs may actually be 18,446,744,073,709,511,616. Either way, it's still a stupidly large number.

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  • That doesn't answer my question, unfortunately. Please, read it carefully again, there's not too much text. May 4, 2017 at 3:38
  • @user1306322 My answer is no, I don't think video URLs get reassigned when a video is taken down
    – Stevoisiak
    May 4, 2017 at 3:42
  • Well, what are your sources for thinking so? Such an answer is as good as no answer at all. May 4, 2017 at 3:50
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Unfortunately, only a person who works with youtube can say this with confidence... But I will give here the answer I believe to be the most likely according to what I've been studying:

My answer is: NO!

Why?

Simple, reusing IDs will hardly bring advantages, in most cases it will only bring disadvantages. I will quote 3:

  1. Reusing IDs weakens (even minimally) the unlisted video system, in which an unlisted video could take an old url, and some people may have saved the url and decide to look again and end up finding a video that it should not have access (probably). This might seem a bit impossible, as the video would have to take a url that existed and should still be unlisted, very unlikely, but still possible.

  2. Youtube has dedicated a lot of its video service to children's videos, so they must be extremely careful with what happens on youtube (especially Youtube Kids). Imagine the following case: a child video is posted and gets a lot of views (obviously from several children), in some cases this child's parents will save the video url for later. Then the video is deleted and another one takes its place, but some user has placed a +18 content that was not blocked by the algorithm and then several parents use the link and have an unpleasant surprise.

  3. According to Youtube, your ID is opaque, that is, it does not provide any information regarding the video or internal things, but, in a smaller case, reuse could reveal the average number of videos that Youtube receives, taking the Video IDs that have been reused and the total number of possible ID combinations it is possible to make a probabilistic deduction of how many videos it receives.

Maybe you might think that some of the drawbacks I mentioned aren't relevant and will never happen, but since this is an app that anyone can use, keep this in mind: if the user gets a chance to make your app don't work as it should, it will!

Anyway, conceptually an ID should neither repeat nor be reused (even with deleted records), future problems will have a high chance of occurring and to fix them will be a huge effort and will increase the code complexity unnecessarily.

How to create a simple algorithm to prevent the reuse and collision of IDs even with deleted records?

Easy! In a database, the primary key will cause duplicates not to occur, so just delete the record data that will not be used and put a "tag" that indicates the record has been deleted (boolean), keeping only what you need to know stored about the respective record (mainly metadata like timestamp).

You might think like this: "But wouldn't I be storing unnecessary information?", well at first it may seem so, but what is an 11-character ID, a boolean tag and some metadata compared to a video? This value is irrelevant, 1 video can be equivalent to millions of deleted records. Furthermore, it is possible to use this information in order to improve the search on youtube using your metadata about the deleted video.

Conclusion

Finally, I believe Youtube does this and maintains some metadata.

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