Because the nextion needs to receive pixels via text commands, the text command overhead is very high. At 115200 bps the nextion maybe able to achieve and process around 460 pixels per second.
Calculating cam capture resolution to yield the time for each frame.
average of 250 bits per pixel to transfer text command for each pixel
width * height = pixels to transfer * 250 = total bits per frame / baudrate = time per frame
320x240 = 76800 * 250 = 19200000 / 115200 = ~167 seconds per frame
160x120 = 19200 * 250 = 4800000 / 115200 = ~42 seconds per frame
80x60 = 4800 * 250 = 1200000 / 115200 = ~ 10.5 seconds per frame.
In conclusion, can the Nextion display a dynamic image over serial - Absolutely.
But certainly not at the speeds shown in the video.
By reading and writing to EEPROM direct via serial I think the average bytes transferred per pixel can be greatly reduced - 512 pixels can be transmitted in one go (with 2 byte color space - more if you use a smaller color space.
Flash memory has only a limited number of write cycles ... :-)
EEPROM was also less than desirable with the added time needed to wait and handle 0xFE and 0xFD while the Nextion prepped EEPROM for read/write, creating noticeable performance drop.