Another "intriguing" dashcam behavior

Module 79L

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Dash Cam
AT11DA, SG9665XS, G1W-H
I take the cards out of the cameras directly into the card readers, to avoid losing them. In both cameras, the card is inserted with the back facing me and in both card readers the card is also inserted the same way, therefore I never see which card is which.
So, due to this, recently I put the 64GB card in the AT11DA by mistake. I only noticed it when I was about to transfer the files to the HDD at the end of the day. There was no problem with the recordings, the files were all there and intact, but there was something different: the file sizes were much larger than on the 32GB card, despite the bit rate being the same.

Here's an example of a 5 min file recorded with each card in the same camera:
Different file sizes with the same bit rate.png

This is the info on both files:
32GB card file size.png 64GB card file size.png


If none of the factors that determine the file size was changed, why are the file sizes different? Does it have something to do with the size of the card? The mind boggles... :confused:
 
Overall bit-rate is higher in 2nd 5min file (13.1 vs 13.7Mbps), probably there was more action depending on scene, there for you got slightly larger file 469 vs 491 Mb which is normal.
 
Today I used the 64GB card again in the AT11DA and looks like there's more to it: all the files (not only the 5 mins ones) had the same 13.7Mbps overall bit rate!

These are the files recorded today with the 64GB card. I only highlighted the ones with 5 mins but they all have the same 13.7Mbps overall bit rate:

64GB files.jpg

These are the MediaInfo reports of the 5 mins files:

64GB files info.jpg

So, the card does make a difference. But why?
 
Exactly as @DT MI mentioned: it's the cluster size. On a large memory card this can be as much as 32767 Bytes, down to 4192 Bytes for smaller capacity memory cards.

The cluster size is usually determined within the firmware as a lookup table for various memory card sizes, and is then applied during formatting. If the card was formatted on a PC (e.g. to FAT32) then the cluster size can be different to the one being applied by the dashcam manufacturer.

A small cluster size will increase the potential for file fragmentation, and requires more read/write steps to dump a recording file to memory. Larger cluster sizes achieve the opposite advantages, at the expense of using up somewhat more memory per recording. Reason being that the space requirements of a recording will rarely ever be an exact multiple of the allocated cluster space, hence there is always a bit of an overflow (unused space) at the end of the last cluster. Bigger clusters mean bigger overflow, hence a larger overall file size for the same recording, but less fragmentation potential and less read/write steps needed for the same recording.
 
Exactly as @DT MI mentioned: it's the cluster size. On a large memory card this can be as much as 32767 Bytes, down to 4192 Bytes for smaller capacity memory cards.

The cluster size is usually determined within the firmware as a lookup table for various memory card sizes, and is then applied during formatting. If the card was formatted on a PC (e.g. to FAT32) then the cluster size can be different to the one being applied by the dashcam manufacturer.

A small cluster size will increase the potential for file fragmentation, and requires more read/write steps to dump a recording file to memory. Larger cluster sizes achieve the opposite advantages, at the expense of using up somewhat more memory per recording. Reason being that the space requirements of a recording will rarely ever be an exact multiple of the allocated cluster space, hence there is always a bit of an overflow (unused space) at the end of the last cluster. Bigger clusters mean bigger overflow, hence a larger overall file size for the same recording, but less fragmentation potential and less read/write steps needed for the same recording.
In that case, how do you explain the fact that the SG9665XS's bit rate and file sizes are the same in both the 32 and the 64GB cards? Shouldn't they be smaller in the 32GB card?
 
In that case, how do you explain the fact that the SG9665XS's bit rate and file sizes are the same in both the 32 and the 64GB cards? Shouldn't they be smaller in the 32GB card?

the cards were formatted in the XS though weren't they?
 
the cards were formatted in the XS though weren't they?
Yes. I never got to format the 64GB card in the AT the second time because that was just a test and I didn't know if it would format the card in exFAT instead.
 
In that case, how do you explain the fact that the SG9665XS's bit rate and file sizes are the same in both the 32 and the 64GB cards? Shouldn't they be smaller in the 32GB card?

Different size memory cards can still have the same cluster size (as determined by manufacturer), so if both cards (32 and 64 GB) are formatted within the XS and then recordings are done to both cards with the same camera then it follows that the file size will also be identical.

The bit rate itself will vary depending on the activity the camera 'sees' - a static picture will use less memory than a moving object, as this allows for better file compression.
 
In that case, how do you explain the fact that the SG9665XS's bit rate and file sizes are the same in both the 32 and the 64GB cards? Shouldn't they be smaller in the 32GB card?

Different size memory cards can still have the same cluster size (as determined by manufacturer), so if both cards (32 and 64 GB) are formatted within the XS and then recordings are done to both cards with the same camera then it follows that the file size will also be identical..

the sizes were the same in the XS

the question came about due to putting a card that was formatted in the XS into the AT and it having a different file size, the cards that were both formatted in the XS both had the same size
 
Ok, did some tests and got to the bottom of this.

Formatted the 64GB card in the AT and, as expected, it changed to exFAT. Overall bit rate in this case was 15.7 Mbps.
exFAT bit rate.png

Then formatted the card to FAT32 in the laptop using GUIFormat...
64GB card file system.jpg

...and the result was: 13.1 Mbps!
64GB FAT32 PC format bit rate.png

Conclusion: the slightly higher overall bit rate of the AT's recordings were due to the 64GB card being formatted to FAT32 in the XS. :cool:
 
I have to say I had my doubts due to the fact that both cameras have the same hardware.
 
You said this in the G1W-H thread, regarding the fact that it formatted the 64GB card to exFAT:
from what I have seen the cameras that are using Novatek chipset that don't have the ability to format large cards FAT32 that still use exFAT (...)
So it's not a chipset limitation? I guess not, since the XS can do it.
 
formatting exFAT on these is unusual, ones I've seen that do this often have problems recycling also so I guess it needs further testing as well
 
formatting exFAT on these is unusual, ones I've seen that do this often have problems recycling also so I guess it needs further testing as well
So, what you're saying is that the normal thing is they format larger cards to FAT32 instead of exFAT? I thought it was the other way around. :)
 
The 'overall bit rate' shown under heading 'General' is the sum of the 'video bit rate' shown under heading 'Video' PLUS the file handling overheads involved to write the data stream to the SD card. Since the same SD card used in the same camera but with different formats (exFAT vs FAT32) produces different overall bit rates (exFAT is higher), it stands to reason that FAT32 is more efficient in this particular situation. exFAT is really of no advantage here as it only makes sense for file sizes larger than 4 GB a piece.

So there are two different things: larger file sizes for same camera with different memory cards due to different cluster sizes, and different overall bit rates for same camera with same memory card due to different formats (exFAT vs FAT32).
 
The 'overall bit rate' shown under heading 'General' is the sum of the 'video bit rate' shown under heading 'Video' PLUS the file handling overheads involved to write the data stream to the SD card. Since the same SD card used in the same camera but with different formats (exFAT vs FAT32) produces different overall bit rates (exFAT is higher), it stands to reason that FAT32 is more efficient in this particular situation. exFAT is really of no advantage here as it only makes sense for file sizes larger than 4 GB a piece.

So there are two different things: larger file sizes for same camera with different memory cards due to different cluster sizes, and different overall bit rates for same camera with same memory card due to different formats (exFAT vs FAT32).
I just included the exFAT info as a curiosity, not as a relevant factor to the discussion. ;)
 
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