Does 2g mobiles don't support quality video calls?

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Just now, my sister called me to have a video call. I turned on my net and started video call. It was very poor quality. Her face was very hazy. Actually, not only her face, but her daughter's face too was hazy. The sound quality was poor too. I had to repeat a sentence 2-3 times to make it audible to her. It was really annoying. She took her headphone and then called me again. She told me that using headphone, the quality of voice seems to get better to her. But, here, me and my mom were facing the same problem. I think it was just because I was using 2g sim, though my mobile is 4g. Was the video call quality bad just because of my 2g sim?