70mai has released firmware version 1.2.136ww for the T800. This is an important update to get installed into your T800.
A couple of weeks ago, it was brought to my attention that the T800 could very infrequently create MP4 files with video stream content that was not playable [black screen video but audio would play]. The issue could occur in the front, rear, or cabin MP4 files. The MP4 files that I used during my review of the T800 did not have that problem.
I created a script that uses the ffprobe utility from the ffmpeg package to quickly scan the T800 MP4 files stored on my NAS drives. The ffprobe command was to simply display the video codec used in the file. This was enough of a check by the ffprobe utility to detect the MP4 files with the video stream issue. Of the several thousand T800 MP4 files on my NAS drives, the script found only small number of MP4 files that in fact did have this problem.
70mai provided some private firmware updates for me to test and gather device log info. Recently, the root cause of the issue was identified and 70mai produced a firmware for me to test with the "fix" in place. The latest test firmware [1.2.135zww] has produced MP4 files with correct/valid video streams. Thank you 70mai for working with me so quickly and diligently to resolve this issue.
I would recommend any T800 user to update their T800's firmware to 1.2.136ww to fix this issue.