that strange because i use OBS to stream and works really fine, my down speed is just 24 and upload 1.5mb, its enough to stream at 720p. go to the options on OBS and change the resolution downscale to 1.25, put frames to 30, and on CBR put 8 of quality. in the broadcast settings what settings do you have? regarding bitrate on video encoding? if you have like 10mb upload you could use a very high value, i use 1100/1200 and run really smoothly.
also try to reduce bitrate for audio to like 128 (if you have higher)
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