Do you have a link to some head-to-head testing showing video quality improvements with 21:9? The theory is pretty straightforward if the file size / bitrate is the same between a 16:9 and 21:9 clip. Cutting off the top and bottom while still recording the same amount of data means that you've got more data per frame with 21:9. I did try it briefly years ago with a pair of identical dashcams and I didn't notice much, but it was only a minimal amount of testing, not anything extensive.
I don't have a side by side video to prove the image quality is better on 21:9, but I know I am on the right side with more Bits/(Pixel*Frame) if using 21:9. Also I have less sky and less dashboard and less motor hood in my videos and the 21:9 aspect ratio is looking more modern than 16:9. For me there is absolute no reason to go back to 16:9 and I would never buy a dashcam which is not offering 21:9 aspect ratio. There was a long fight with Viofo to include the 21:9 aspect ratio.
By the way, if you plan to watch 21:9 videos multiplexed as 2CH or 3CH when you will play them on the PC you will need some adjustment to obtain the correct aspect ratio. In the
MPC-BE, the settings are showed in these screenshots:
These settings were created by me in MPC-BE at Pan & Scan Presets menu by pressing New, writing those values and then Set and Save.
The above setting is in the Pan & Scan menu of the player by right clicking on the video image.
When editing such a 21:9 Multiplexed footage you will need to correct the aspect ratio in your editing software. I don't know how to do this properly in an editing software, but the resulted 2CH video should have these properties:
A:
Original video: 7680x2160 Aspect ratio: 3.556
Encoded video: 7680x
2160 with a
forced Aspect ratio:
4.8 (this 4.8 flag must be embedded in the video). Such a video is Anamorphic type, this was common on many old DVDs when the movie aspect ratio was 2:35 but it was encoded as 4:3 and the player played it as 2:35. So this is old technology.
or
B:
Original video: 7680x2160 Aspect ratio: 3.556
Encoded video: 7680x
1600 with
resulted Aspect ratio:
4.8 (no need for any value of the aspect ratio to be embedded in the video)
As you can see the resolution of 2CH multiplexed video is always 7680x2160 no matter if the original source is 21:9 or 16:9. I don't expect this to be fixed in the firmware. So the advantage of 21:9 Bits/(Pixel*Frame) is lost when multiplexing but remains in separate videos.
In VSDC the only way I found it was to load the video and at the encoder tab I set the new resolution of 7680x1600.
Of course, after doing such correction of the aspect ratio, all data printed on the video will be oblated.
Normally all players should play the video by reading the aspect ratio and displaying the video image properly with the correct aspect ratio but if you want to be on the safe side it is better to reencode it by manually setting the new resolution.
For me, the only way to set the aspect ratio of a MP4 video was to convert it to MKV using MKV Toolnix and put the 4.8 aspect ratio in the settings before saving. Unfortunately, the VSDC editing software and maybe many editing software are not reading the aspect ratio of a video, but only the players are doing this properly.
Normally such an Aspect ratio flag should be also in the MP4 container but I couldn't find the proper tool to embed that flag in an MP4 video. The latest tool I used was YAMB, many years ago but it is outdated. Most of the software found for editing the MP4 header and adding tags, are for the music but not for video aspect ratio. The MP4 standards are allowing forced aspect ratio (display aspect ratio).