For HLS you can use mpeg ts, but mp4 is also an option (with the problem you talk about). IMO one of the issues is that transcoding to lower resolutions usuall

For HLS you can use mpeg ts, but mp4 is also an option (with the problem you talk about). IMO one of the issues is that transcoding to lower resolutions usually happens on the server side. That takes time. If the client transcoded that latency would go away (mostly).