They are all broadly similar, all being based on the ESP32-D0WD core, but have
some subtle differences between variants around PSRAM inclusion and camera pin
mappings.
The ESP32CAM "unit" product (SKU: U007) has no PSRAM and maps the
"Pixel Data 0" (Y2 GPIO/OV2640 D2) camera pin to IO17 rather than IO32 as is
the case with most other M5Stack ESP32 camera devices.
The ESP32CAM also requires the "hmirror" and "vflip" camera configuration
bits setting in order to capture a true image.
The relevant M5Stack pin configuration documentation can be found here:
https://docs.m5stack.com/#/en/unit/esp32cam?id=pinmap
The boundary delimiter (_STREAM_BOUNDARY) needs to be send before the
body part (_STREAM_PART) too follow RFC2046. This caused ffplay/ffmpeg
to fail to open the MJPEG stream.
