Chronos > Software Dev

"Missing" the out point when saving.

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tesla500:
These cards have been working very well:

http://www.lexar.com/products/memory-cards/sd/Lexar-Professional-633x-SDHC-SDXC-UHS-I-cards.html#SKU=LSD32GCB1NL633

oakwhiz:

--- Quote from: tesla500 on June 25, 2017, 04:33:46 PM ---These cards have been working very well:

http://www.lexar.com/products/memory-cards/sd/Lexar-Professional-633x-SDHC-SDXC-UHS-I-cards.html#SKU=LSD32GCB1NL633

--- End quote ---

I'd like to second this, I have had very good experiences with these cards.


--- Quote from: tesla500 on June 23, 2017, 11:41:00 PM ---That is known to happen when the card becomes completely full during save, and potentially if the card doesn't have enough write speed. It seems quite rare though, if you find a way to reliably duplicate it, let me know!

--- End quote ---

I'd also like to elaborate on this, the technical reason for this issue seems to stem from the disk not being able to answer requests in time. Good quality SD cards are able to maintain a certain minimum constant I/O bandwidth, but lower quality SD cards operate in fast bursts followed by periods of inactivity (they probably have internal SRAM cache to make up for the fact that they have poor flash block erase performance.) If the disk blocks on I/O then two things happen: the encoder buffers start to become full, and a certain piece of code feeding frames to the encoder tends to get stuck in an infinite loop when frames are dropped. The encoder is synchronous, but we are working on a way to add flow control. This would enable the encoder is able to pause the flow of frames from RAM when the encoder is unable to push frames onto the disk.

nik282000:
Thanks for the explanation, it covered my next question. The USB key I am using is USB 3 which I would have thought would be fast enough but it seems to only be 99 times out of 100 (still not bad). Is there a bottleneck in USB that the SD card interface lacks? I'm glad to hear that you guys are working on flow control for slower storage devices, thanks!

Electra:
As far as I know, the camera only has a USB 2.0 port. Without knowing internals of the processor, USB should have better throughput than SD,  However the big limitation seems to be the encoder and I seem to recall much over about 12Mb/s(I'm likely wrong.) won't make any difference. My 80Mb/s cards write no faster than 40Mb/s ones. 

USB drives have hugely different write speeds and it's not as well documented as on SD cards.  I've got old USB 2 drives that write faster than huge but slow USB 3 drives(They /read/ fast, but write is bad). There should be utilities/benchmarks out there to test them, but you'll need to find one for your platform.

oakwhiz:
Another manifestation of this issue: if your saved footage has a random or semi periodic stutter in it, your disk is too slow, and the encoder is skipping frames as a result.


--- Quote from: Electra on September 07, 2017, 11:02:36 PM ---My 80Mb/s cards write no faster than 40Mb/s ones. 

--- End quote ---

It's true that this is a limitation of the encoder. It may be technically possible for a lossless compression algorithm to surpass the encoder's speed, but at the cost of SD card free space. We are looking into various lossless compression options such as linear predictive coding over YUV color space data, or raw bayer data.

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