I think Zoom doesn't use WebRTC, they have their own decoder, transmission, retry layer. If you try to transmit raw frames directly, you end up with codec issues since frames have dependencies among them. E.g. VPX series cannot decide frames without a golden frame or a key frame so these need to be kept as state for a decoder. Every other intra-frame needs to refer to these frames and there's no limit usually as to how many intra-frames one can have between inter-frames (key-frame or a golden frame).