I have a Data rate/Bitrate question

[Honk]

Hello folks,

I have a Data rate/Bitrate question.

Does Data rate/Bitrate fluctuate based on the ratio of black area to light area in a video?
I ask because I see variations in the numbers when a look at the properties of various mp4 files.

The images below show the properties of 2 series of 30 fps 4k videos using Auto settings, captured on different dates using a Mini 2.

These videos of varying lengths were captured during daylight hours. They all show Data rate/Bitrate of approx. 100mbps with slight variations.

These videos of varying lengths were captured during a late evening sunset with a lot of black area below the horizon. They all show much lower Data rate/Bitrate numbers and of wide variations. The "Sunset.mp4 is a compilation of the 4 videos to the right made using Shotcut.


Thank you very much!

 

[SmilingOgre]

I’ve not researched mp4 compression in regard to bitrate so I can’t comment directly. I do however do a lot of video in Black Magic raw where one can record in either constant bitrate or constant quality. Constant quality will vary bitrate dependent upon the amount of detail in the image. It is not a function of dynamic range directly.

 

[Ralph thompson]

mp4 applies a lot of compression to make smaller files. If the image has lots of similar colours like a lot of blue sky, deep shadow or a lot of white then the compressed image will be quite small so there is less data and so a smaller bit rate. If the image has lots of detail like roads, trees, cars, no sky etc then this cannot be compressed as much so the file size is larger, hence larger bit rate.

 

[Kilrah]

Encoders as configured in DJI things and most other cameras target a specific bitrate regardless of content.

Looking at filenames it looks like this has gone through the Fly app, so likely some files are untouched originals that were downloaded from the aircraft (those at 100Mbit) while the others may have been processed in the app and exported from there, which will have reencoded them at the lower bitrate.

 

[Honk]

Thank you all for your insights and clarifications for me. Very helpful.
Can I deduce that those numbers do not reflect or indicate the fidelity/resolution of the images?

@Kilrah
>>Looking at filenames it looks like this has gone through the Fly app, so likely some files are untouched originals that were downloaded from the aircraft (those at 100Mbit) while the others may have been processed in the app and exported from there, which will have reencoded them at the lower bitrate.
Thank you. They were all downloaded from the Fly app except the Sunset.mp4 which is the result from Shotcut video editor.

Thanks again.

 

[Kilrah]

A lower bitrate is usually going to be lower quality, but there are many other factors at play.
Typically when you make an edit you want the best possible source, so... just get the 100MBps files from the aircraft's card.

 

[Honk]

A lower bitrate is usually going to be lower quality, but there are many other factors at play.
Typically when you make an edit you want the best possible source, so... just get the 100MBps files from the aircraft's card.

Ah ha. Thank you.