The video is encoded to only play on a very specific worldline.

Worldline at the start of the game, before the first D-Mail has been sent:
1.130246

Worldline when Okabe jumps from Alpha to Beta after deleting the Echelon log:
1.130205 (Kurisu/True Ending)
1.130238 (Mayuri Ending)

Worldline when Okabe and Suzuha time travel backwards to July 28, fail, return, and watch the video:
1.130209 <- Video encoded to only play on this worldline

Worldline when Okabe and Suzuha time travel back to July 28 again:
1.130212

Worldline when Okabe succeeds (the Steins Gate Worldline):
1.048596