The audio volume when I playback a video recorded with UR22c is very soft

Update to my problem:

Upon further investigation, I found that the video/screencast recordings are good as when I playback on my iMac’s built-in speakers, the audio sounds good. But when I changed the audio output to the UR22c with an ATH-M20x headphone, the volume become soft again. The UR22c with the ATH headphone can hear YouTube alright.

What could possibly be the reason for this happening?

I just got my UR22c and this is my first time using an audio interface. I met the problem as described in the title. These were my settings.

  1. Dynamic mic connected to Channel 1, with gain tuned slightly beyond 8(the 8th marking on the knob).
  2. Mono on. I understand this is for direct monitoring. When playing back an audio or video, this should be turned off.
  3. Phone knob is turned to 9.
  4. Output knob turned to about 7(there isn’t any markings on the knob).

I found out that when I record a pure audio file using Cubase or other audio apps (Logic and Quick Time), the audio playback volume is audible. But when I record a video(a screen recording or with the Mac’s camera) with audio using Quick Time and iPad Pro, the audio volume is extremely soft, barely hearing some sound but not able to make out the words said. When I playback the same videos without connecting to the audio interface, the volume sounds alright, similar to pure audio recordings.

I would add that playing back a video e.g. YouTube sounds normal to me through my headphones connected to the UR22c.

Is there some settings that I did wrongly?