There's definitely some kind of file/data embedded in Space.mp4, with ffmpeg, I can do:

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In addition, I think I found the original copy of the video file (before extra data was embedded into it):

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9356135-7209006 = 2147129, which is the number found in Number.txt

So, there are 2147129 bytes of additional data besides the audio and video streams in Space.mp4

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Edit: extract the extra data with this: