Which low-level library for thumbnails

[Alexandre34]

Hello.
I am newbie with Raspberry, and need an advice.
Which library should I use and manuals should I read for a low-level thumbnail project inC/C++ ?
My project, at the same time:
Display (HDMI output) a movie in rectangle 1 (0,0,200,100)
Display a animated GIF in (0,200,200,100)
Display a picture (PNG) in (0,100,200,100)
and overlaying a frame buffer (subtitles, captions, labels) in (0,80,200,20)

As the project is a standalone loop player, I dont need high level library. The more basic, low level, is the better.
Best regards

[-rst-]

Maybe the examples https://www.raspberrypi.org/documentation/usage/demos/ are low level enough.

I'd probably still look at Qt5 or Kivy...