Geebax
Captain
Australia
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gyrex Posted at 2018-7-9 07:36
How do you know it's got no buffer? It has to have some kind of buffer from the sensor, there's no way it would write directly from the sensor to the SD card, there'd be so much rolling shutter if this was the case while it waits to write each frame of a video.
The Samsung 128GB cards sustain 90MB/s write speeds and 100MB/s read speeds, I've tested this using dd. Most decent brand cards (Sandisk, Toshiba, Samsung etc) sustain the speeds they quote. SD cards aren't like hard disks which could potentially deliver fast burst speeds when reading and writing to the buffer but suffered degradation when the buffer filled and had to write to the platters.
First of all I know what is inside the image processor, and secondly, the disc sub-system is not writing frames to the card, it is writing an MPEG transport astream. And to write it successfully, it must be able to keep up with the stream bitrate, and you cannot use a buffer to do that when it runs continuously. For writing long period streams, a buffer will over-run if the destination media cannot sustain the writing speed.
I agree that the cards you mention are good quality and will most likely sustain the speeds quoted, but not all m,anufacturers are as honest with their specs. Even Sandisk have slower cards that cannot keep up. If a card cannot keep up with the stream rate, it simply stops recording. |
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