Hi Dusan,
when you change from 16 bit to 24 bit, the Quality is increased (and the computer have to "work" a little more). But, to my knowledge, this can NOT change the Tuning.
If not done this, I recommend to test the 44.1 kHz / 16 bit setting (CD quality), but if the computer has enough power, I would always use 24 bit resolution.
And don't forget to check also the settings in the Windows Control Panel / Sound, as mentioned above.
If the tuning problem persists, you could try some other Audio Player programs, e. g. VLC Player or Winamp and playback some MP3 files (you know the key). In this way you can check, if the tuning problem concerns the whole computer, or maybe just the YT player. If it's only with YT, I would try another BROWSER first.
By the way: At some Video Players the playback SPEED can be adjusted, and in some cases this also changes the PITCH/TUNING. So, please make sure that the Player (e. g. YouTube) is running at normal speed.
Best regards,
Chris