Question on SD card speed needed.

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flyboy320

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I have a Blackvue DR3500 with custom firmware and it has a bitrate of about 13MB/s. If I'm looking for a microSd card, do I need to look at the write speed and get one that can be written to at least 13MB/s?

I'm a bit confused on the recording data rate of the camera and how that applies to the required write speed of the card.
 
I think you are confusing the bitrate of the camera thats in Mb/s ( megabits / second ) and the MB/s ( Megabytes / second ) thats the mesurments for SD cards and how much data they can read / write every second.

At 13 Mbits bitrate of a dashcam you dont get anyway near to 3 Megabytes of date needing to be saved every second, so a regular SDXC class 10 / U1 should do just fine, at least it have been so in all of my dashcams.

You can go faster if you wish, its allways nice to have good transfer speeds from the card in the card reader and to the PC.
This is not least most true if you drive for long time and want to save it all for a journey / trip video, but for normal day to day where you only pick a 3 minute file here and there containing some traffic dumbass, overall speed of the SD card is of lesser importance.

Just took a look of one of my 3 minute files.

The average bitrate of the recording is 15 megabits, and the file is 340 Megabytes in size, so thats 340 MB divided with 180 seconds ( 3 minutes ) so thats only 1.8 Megabytes written to my SD card every second, far less than my Kingston SDXC class 10 / U1 can handle ( think it have a write speed of 10 Megabytes / second )

I know many dashcam makers recomend SD cards with writespeeds of 30 - 40 MB/s but thats just insane even for a 4 K dashcam thats not even made yet.

I have seen file sizes just over 500 MB from the same camera as above mentioned 3 minute file, but that was with 25 Megabit firmware, and even that is well below 5 Megabytes of data needing to be written to the SD card every second.

Extrapolating on those values a 50 mbit recording will generate a little over 1000 megabytes / 1 Gigabyte for a 3 minute recording, and thats still only 5.5 Megabytes of data needing to be written to the SD card every second.

So a kingston SDXC class 10 / U1 like the ones i have a fjew off should be able to handle around 90 Mbit bitrate, and thats allmost up where Sony and Gopro action cameras are when they record 4K footage at the highest bitrate.

I have just gotten a 64 Gb kingston clas 10 / U3 card, that one can handle 90 MB/s read speeds and 80 MB/s write speeds, well over what current 4 K action cameras can crank out of data.
And it was only like 100 DKkr more expensive than the normal U1 cards i use.
 
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kamkar1 said:
I think you are confusing the bitrate of the camera thats in Mb/s ( megabits / second ) and the MB/s ( Megabytes / second ) thats the mesurments for SD cards and how much data they can read / write every second.

At 13 Mbits bitrate of a dashcam you dont get anyway near to 3 Megabytes of date needing to be saved every second, so a regular SDXC class 10 / U1 should do just fine, at least it have been so in all of my dashcams.

You can go faster if you wish, its allways nice to have good transfer speeds from the card in the card reader and to the PC.
This is not least most true if you drive for long time and want to save it all for a journey / trip video, but for normal day to day where you only pick a 3 minute file here and there containing some traffic dumbass, overall speed of the SD card is of lesser importance.

Just took a look of one of my 3 minute files.

The average bitrate of the recording is 15 megabits, and the file is 340 Megabytes in size, so thats 340 MB divided with 180 seconds ( 3 minutes ) so thats only 1.8 Megabytes written to my SD card every second, far less than my Kingston SDXC class 10 / U1 can handle ( think it have a write speed of 10 Megabytes / second )

I know many dashcam makers recomend SD cards with writespeeds of 30 - 40 MB/s but thats just insane even for a 4 K dashcam thats not even made yet.

I have seen file sizes just over 500 MB from the same camera as above mentioned 3 minute file, but that was with 25 Megabit firmware, and even that is well below 5 Megabytes of data needing to be written to the SD card every second.

Extrapolating on those values a 50 mbit recording will generate a little over 1000 megabytes / 1 Gigabyte for a 3 minute recording, and thats still only 5.5 Megabytes of data needing to be written to the SD card every second.

So a kingston SDXC class 10 / U1 like the ones i have a fjew off should be able to handle around 90 Mbit bitrate, and thats allmost up where Sony and Gopro action cameras are when they record 4K footage at the highest bitrate.

I have just gotten a 64 Gb kingston clas 10 / U3 card, that one can handle 90 MB/s read speeds and 80 MB/s write speeds, well over what current 4 K action cameras can crank out of data.
And it was only like 100 DKkr more expensive than the normal U1 cards i use.
Click to expand...

Fantastic explanation, thanks a million. You were right, I was confusing Mb/s and MB/s. ;)
 
One up on Kingtson...very good card.
 
It might record at 13 Mbps, but what speed does it actually save to the SD card?
How much does it buffer and how much time can it spend on purely writing?

Maybe Jokiin could explain that a bit more in detail?
 
So in order to write 15 Mbps (in your thread), which is 1,875 MB/s, you should use a memory card with a continuous write speed of at least 6 MB/s.
That's over 3 times as fast as the video stream from the camera.
 
People confuse bits and bytes, class 4 cards are capable enough for the speeds that most cameras write at anyway, most of the cards these days are class 10 though so more than enough
 
Yes today its pretty hard to buy a card slow enuff, but the much larger performance overhead on modern cards dont really come at a mentionable additional price.
For instance try to look at the price for a 32 Gb SDHC card Vs a simmilar sized but in the newer & "faster" SDXC type.

Here the cheapest 32 Gb micro SDHC class 10 / U1 ( 45 MB/S read - 10 MB/s write ) "kingston brand" is 94 DKkr ( 9 pounds )
And the cheapest 32 Gb SDXC class 10 /U1 ( 45 MB/s read - 10 MB/s write ) " kingston brand" is 145 DKKr ( 14.7 pounds )

BUT ! if you pay 120 DKkr more you can get the same card as my new one 64 Gb SDXC class 10 / U3 ( 90 MB/s read - 80 MB/s write ) "kingston" at 285 DKkr ( 29 pounds )
Thats 2 X the storage capacity and a much faster read/write speed for 12 pounds, compared to the 32 Gb SDXC class 10 /U1, in my mind thats well worth it, And your memory card is 100 % future proof as i dont know of any consumer camera that need those fast read / write speeds.

You can find SD cards with speeds as low as 4 MB/s, but imagine transferring 32 Gb of data at that speed from your SD card to your computer.
I myself have no time for that and thats why i will be updating all my cards to SDXC class 10 / U3 cards as they die on me, okay thats allso mean i have to update my old card reader cuz the one i have now cant handle those speeds, it can handle the type of memory card but not the speed of class 10 /U3.

I can recomend the SDXC class 10 /U1 cards as they are plenty for 99% of all dashcam and action cameras.
BUT ! personally i will go for the much faster class 10 /U3 cards as i think the added price is worth it comparing the added read/write speed i get.

O and dont go on ebay or what ever and buy the cheapest card you can find, there is a lot of fakes out there, so by the card at a local B&M store and get your national warrenty minimum and/or the extra the maker have ( lifetime in some cases )
Making a RMA on a SD card to some Chinese site is a pain and will cost way more than a new card will cost, and it will take a loooong time.
 
kamkar1 said:
You can find SD cards with speeds as low as 4 MB/s, but imagine transferring 32 Gb of data at that speed from your SD card to your computer.
Click to expand...
I don't know about other people but I bought Class 10 cards for the cameras only because of their transfer speed to the computer, not because I needed high speed writing.
I already had a 32GB Sandisk card when I bought my first camera and I don't even know what class it is (it doesn't say in the card). All I know is it transfers at about 9MB/s and it takes "ages" to transfer the files, even at that speed. The class 10's transfer speed is between 15 and 20.
 
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