It's not the same constraints. With video transcoding you push batch jobs that can be processed at any time. The video is taken from a S3 bucket and the result

It's not the same constraints. With video transcoding you push batch jobs that can be processed at any time. The video is taken from a S3 bucket and the result is put back in another place. When transforming the video you might use some heuristics on the whole file (because some formats have the metadata at the end). You can also implement fallbacks when the transcoding fails. With live streaming you need to acquire a streaming video source, transform it in real-time and forward the stream without too much latency and without failure. Then you need to push that stream to the N connected people possibly fanning-out the traffic to multiple servers to dispatch the load.