This is because of T153747, which is resolved and the patch will be deployed on 2 January. And I believe transcoding has been intentionally halted due to T153488.

This is known, and being worked. It's simply that the backlog became extremely large due to a high number of 'huge' (1920P, and an hour long) and a (resolved) bug that caused the servers to try to start an insane number of concurrent tasks. More transcoders have been added to the cluster, and the backlog should fall over time. Transcodes marked as "Added to Job queue [INVALID] ago" are indeed being run, there are just 10k tasks in the queue.

Okay, thank you very much for this information.

In T153852#2893196, @Revent wrote:

It's simply that the backlog became extremely large due to a high number of 'huge' (1920P, and an hour long)

They are not 1920p (that would be impossible to transcode for a hour long video), most are 720p, which is still large. Well, atleast the White House don't make their hour-long videos 1080p nor 1920p...

@Pokefan95 When I said 1920P, https://commons.wikimedia.org/wiki/File:Moscow_Ring_Railway_full_trip_-_view_from_ES2G_train.webm is actually the one I was thinking of... which yes, is not actually 1920P (which is not a real thing), but it is a 2.5GB full-HD video... I was vaguely making the point of 'insanely large files' in a very generic manner.

(Just a note about the terminology: 1920 x 1080 px is usually referred as 1080p, as the number refers to the vertical dimension instead of the horizontal. Horizontal resolution is usually referred by eg. 4K)