I blamed my NAS for slow streaming until I realized what transcoding was actually doing

When self-hosting media on a NAS, slow or buffering playback is almost never caused by the network or hard drives — it's transcoding. Transcoding involves two CPU-intensive steps: decoding the source file into raw pixel data, then re-encoding it into a format the client device supports. On low-powered NAS CPUs, this causes CPU saturation, thermal throttling, disk I/O contention, and RAM pressure. Solutions include enabling Direct Play or Direct Stream on compatible clients, upgrading to a modern streaming device (like Apple TV 4K), or adding a GPU to offload transcoding — noting that Plex requires Plex Pass for hardware transcoding while Jellyfin does not.