I haven't had much to do with Arduino, although I am well-versed in other types of analog and digital electronics.
What I need is a system that can directly read a string of bytes from a .txt file stored on an SD card, at a rate of at least 8 Megabytes per second.
All of the Arduino projects I've seen that access the SD card seem to run at a much slower rate, but cameras and the like have much higher access speeds, so it must be possible.
On "playback" the bytes would be presented as a series of 8-bit words feeding a simple digital-to-analog converter, which would generate a video signal.
The idea is to produce a simple and cheap way to convert standard modern video into some of the old pre-war TV standards, for use by vintage TV enthusiasts.
The general idea is that the video would be first rendered into a string of stills by a program such as FFMPEG, and then a PC would re-render the frames into a series of still that recreate the old TV standards.
They would then be stored on an SD card as a simple string of bytes, basically as a .txt file.
The re-rendering wouldn't be done in real time, but most video rendering isn't.
Basically, the TV enthusiast would have a collection of SD cards, which would be played more or less like pre-recorded videotapes.
I seem to recall that there are 2 methods of reading/writing to/from an SD card. For us it's the slower method that you see in all the SD libraries. For others such as camera, phone & tablet manufacturers, there's the second method that is faster. As far as I know, the information required to implement this faster method is protected by NDA.
Of course, things could have moved on since I last played with low level SD card drivers.
the answer is Not yet, but here are some forum that try to achieve more than normal speed
https://arduino.stackexchange.com/questions/28540/how-to-increase-sd-card-write-speed-in-arduino
https://forum.arduino.cc/index.php?topic=66241.0
https://forums.adafruit.com/viewtopic.php?f=31&t=21728