Dashcams' write speed

Module 79L

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#1
How do you calculate it? Is it fixed or depends on things like the bitrate, the resolution, the type of chipset, the firmware, etc?
 

kamkar1

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#2
Take a 3 minute file, let say it is 340 MB in size, divide that with the 180 seconds that make up 3 minutes, and you have the amount of Megabytes / second the camera have been writing at.
Memory cards as you know list their speeds in Megabytes/ second.

In this example that would be a write speed of 1.88 MB/ second the camera have been writing.

Off course if the camera use variable bitrate you will see different file sizes, but daytime driving should provide the worst case scenario, night time recordings file size can be significant smaller with a VBR camera.

If it is a VBR camera then in parts of that 3 minute recording the camera might have been writing at 3 MB/s and then other parts it might only have been writing at 0.8 MB/s

The above are the average write speed you are getting, but if your action in the footage have been the same thruout the 3 minute recording you can also be sure the bitrate the camera have chosen to use have been pretty much the same.
 
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Module 79L

Module 79L

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#3
So, are these calculations right or wrong:
Each 3 minute file is around 360Mb,
There are 8 bits in a byte, so 360 x 8 = 2880 Megabits of information to write to the card over the 3 minute period,
There are 60 x 3 = 180 seconds in 3 minutes,
This means that 2880 Megabits need to be written over 180 seconds leaving an absolute minimum write speed of 16Mb/s.
 

Nigel

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#4
So, are these calculations right or wrong:
Looks OK, however the mbps are given in the file properties, sometimes given in kbps so you need to divide by 1000.

If it is a variable bitrate file then you really want the maximum bitrate, there is a application called "Bitrate Viewer" which will show you more detail of what is in the files.
 
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Module 79L

Module 79L

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#6
correct but confusing due to Mb or MB, 16Mb/Sec is only 2MB/Sec, similar numbers to the example @kamkar1 provided although he explained it clearer
So, in which value is the microSD cards' write speed expressed in? MB/s or Mb/s?
 
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jokiin

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#10
This is why camera sellers need to provide compatible cards with their cameras to eliminate so many headaches in future
we like to include cards is to make sure people have the right type of card, but mainly to make sure they get a genuine card, so many fakes out there
 

Hombré

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#13
Unfortunately most camera failures that I see on this forum seem to relate seem to the card
it will quickly identify a fake capacity card, and can often help to identify a poor performing card
Once again..... Fakes will be eliminated with a supplied card by the manufacturer
 
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