Hand-waving away facts again I see!
1. A typical US cruise missile is only 13 to 21 ft long.
AGM-86 - 20 ft
AGM-158 -14 ft
BGM-109 - 20 ft
2. The width of the Twin Tower building was 208 ft, therefore the apparent size of the cruise missile would be between 1/10th and 1/14th the apparent width of the Tower (
if it was side on to the viewer. Anything less than side on and the apparent width will be reduced).
3. The absolute best, highest resolution video camera available in 2001 was the Panasonic Broadcast AG DVC10. It had 3 x 1/4-inch CCDs, ~270,000 pixels per CCD - one for each colour; R, G and B
[*] (that is 270
kilopixels - about a quarter of a megapixel). Shooting in 16:10, which is what your video looks to have been shot in, that would be about 650 x 400, in other words 650 pixels across the video, and 400 pixels down.
4. The apparent width of the tower, on your video is 1/27th of the width of the video, so it is approximately 24 pixels wide. Since the Tower is 208 feet, and the wing span of a 767 is 159 feet, that aircraft would appear to be about 18 pixels wide. The biggest of the cruise missile is 20 ft, and that works out to... 2 pixels! Your missile would only be two pixels wide at absolute best.
5. In reality, looking at the viewing angle, a cruise missile would not be side on, it would be almost head on - less than a pixel. Even a forensic examination of the video would be extremely unlikely to detect it.
6. To help you visualize this I have drawn some lines on the previous image I posted...
The red line is the width of 767's wingspan (compare it with the dark shape above it). That dark shape is EXACTLY where I would expect your missile to be, given the frame-grab you posted that you claim shows a missile impact
The white dot below the red line is how big the missile would appear. The dark shape is CLEARLY far too big to be your missile, but is about the right size to be an airliner.
Debunked again!
[*] The Panasonic Broadcast AG DVC10 used full-frame dichroic filters to better separate the red, green and blue color bands, and to get better low-light performance.