The video starts with the vehicle already stationary in the box, it then starts moving and stops again. The contravention is at the point of entry, which was not at 3:29, it must have been 3:28 or earlier, therefore this is an easy challenge:
Dear Royal Borough of Greenwich,
The video confirms my vehicle did not enter any box junction at 3:29, on the contrary the video confirms my car had already entered the box junction at 3:28, and unfortunately the video does not show the point of entry, which must have been before the start of the video.
Furthermore, the video shows that there was space beyond the box which my vehicle could have used to exit the box, I did not make use of this space as doing so would have involved cutting in front of the bus.
As no contravention of entering a box occurred at 3:29, the contravention alleged on the PCN did not occur and the penalty charge must be cancelled.
Yours faithfully,
Send it online and keep a screenshot of the confirmation screen.