What are these hardware components, and how do I control them?
Yes, you've identified the subsystems correctly. On the main PCB, the "black areas" are individual chips.


  "hynlx" 512A KOR (I guess Korea)


This is an SDRAM chip, used by the firmware on the SOC in general, and in particular as a frame buffer for the decoded video.


  SAMSUNG 031 PCBO


This is a flash EEPROM chip, which contains both the firmware for the SOC and the video file.


  ATJ2273B-C 


This is the main processor (system on chip, or SOC).

It contains a general-purpose CPU, along with USB, SDRAM, audio and video display controllers, and it "runs the show".