Codecs and performance

Which video codecs and hardware encoders Roomler uses on Windows, macOS and Linux — and what to change when a remote session feels slow.

Roomler encodes the remote screen as video and decodes it in your browser. Which encoder it uses depends on the machine’s hardware, and it is chosen by probing rather than by guessing.

Codecs

Codec	Notes
H.264	The universal floor. Available everywhere, decodes everywhere.
HEVC	Better quality per bit; needs support on both ends.
AV1	Best compression; newest hardware only.
VP9	Used for the 4:4:4 path, where crisp text matters more than motion.

A codec is only offered when both ends can handle it, so a session always negotiates down to something that actually works rather than failing.

Hardware encoders by platform

WindowsmacOSLinux

The broadest support of the three. On startup the agent probes what the machine can really do and advertises only what succeeded.

Media Foundation H.264 — the built-in hardware path.
NVIDIA, Intel and AMD encoders for H.264, HEVC and AV1 where the GPU and driver provide them.
Software (openh264) as the always-available floor.

Force one if you need to:

powershell

roomlerd run --encoder hardware   # try hardware first
roomlerd run --encoder software   # skip hardware entirely

Encoding is software-only on macOS today

The hardware-encoder dispatch covers NVIDIA, Intel and AMD; VideoToolbox is not wired up, so Apple Silicon encodes in software (openh264 for H.264, libvpx for the VP9 4:4:4 path).

It works well for normal desktop use. It is a real limit for high-resolution, high-motion content, and it is stated here rather than left to be discovered.

NVIDIA, Intel and AMD hardware encoders are used where the driver provides them, with software as the floor.

The agent’s capability probe runs in a separate process on purpose: a graphics driver that faults while being probed then takes down the probe rather than the agent. Before that, a bad driver could restart the agent straight back into the same probe — a crash loop rather than a degraded machine.

Why a probe rather than a list

Reporting a codec as available because the hardware ought to support it is how you get a session that negotiates a format and then produces nothing. The agent therefore encodes an actual frame with each candidate at startup and advertises only what worked.

When a session feels slow

Work down this list — it is ordered by how often each one is the answer.

Check the connection indicator. If it reads Relay, the path is the problem, not the encoder. A relayed pair is bandwidth-capped by design. See cannot connect.
Check what the far end is doing. A machine pinned at 100% CPU encodes slowly no matter which encoder it picked.
Set priority to Responsiveness. Trades sharpness during motion for input latency.
Reduce the resolution at the far end. A 4K desktop is four times the pixels of 1080p, and on a software encoder that is the whole budget.
Try forcing hardware encoding on Windows or Linux, in case the probe fell back for a reason worth knowing.

"Slow" almost always means "relayed"

Across a lot of field measurement, the overwhelmingly common cause of a sluggish session is a pair that fell back to a relay — very often because a VPN client on one end captured the local network range. The same two machines on a direct path are typically an order of magnitude better. Check the indicator first.

Browser-side decoding

The viewer uses a low-latency decode path in Chromium that bypasses the video element’s built-in buffering.

Why Chromium specifically

A normal <video> element enforces a jitter buffer of roughly 80 ms regardless of what you ask for, which is a large share of a remote-control latency budget. Decoding frames directly and painting them avoids it. That path is a Chromium capability, which is why the viewer targets Chromium even though the rest of the product is browser-agnostic.

What a good session looks like

Path	Round-trip input latency
Same LAN	Single-digit milliseconds
Direct across the internet	Roughly the network round-trip, plus encode and decode
Relayed	Noticeably higher, and bandwidth-capped

If a LAN pair feels slow, something is wrong and worth reporting. If a relayed pair feels slow, the fix is to get it off the relay.