YouTube Dual Stream
YouTube Dual Stream publishes a horizontal 16:9 version and a vertical 9:16 version of the same live broadcast at the same time. Desktop and TV viewers get the widescreen picture, and mobile viewers can watch the vertical version in the YouTube mobile app.
Choose Auto to derive vertical video from your horizontal input, or Encoder to supply a separate vertical feed. Only Encoder needs two stream keys.
What YouTube Dual Stream actually does
An ordinary YouTube live stream has one shape. If you stream 16:9, mobile viewers watch a small widescreen rectangle with black space around it. If you stream 9:16, desktop viewers get a narrow strip. Dual Stream removes that choice by carrying both shapes inside one broadcast, so YouTube can serve whichever one suits the surface the viewer is on.
Both orientations share the broadcast identity: one title, one chat, one set of live analytics. What differs is the video itself. The horizontal feed and the vertical feed are two distinct video streams. In Encoder mode, each incoming feed has its own stream key.
That is the conceptual core of dual format streaming in general, covered in what is dual format streaming. YouTube's implementation is one platform's version of it.
Set up YouTube Dual Stream
- Open YouTube Studio > Go live and check Dual stream under Stream settings before starting.
- Use Auto for a vertical version derived from your horizontal input. Check the vertical preview and adjust its layout.
- For a separate portrait composition, select Encoder in the vertical preview and choose a second stream key. Use RTMP(S) and send each orientation to its matching key.
- Check both pictures before going live. You cannot add the vertical format after the stream starts.
Both orientations share a broadcast URL and live chat. Turn off Dual stream under Stream settings if you want horizontal only. See YouTube's dual-stream instructions.
When you need two stream keys
In Encoder mode, separate keys identify the two incoming pictures. Auto needs only the horizontal input.
The horizontal key
The familiar one. It behaves like any normal YouTube live stream key and carries your 16:9 feed. If you have streamed to YouTube before, nothing about this side changes.
The vertical key
Only exists once Dual stream is enabled, and only if you set the vertical source to Encoder rather than Auto. Auto means YouTube builds the vertical picture itself and no second key is involved.
This is the practical difference from Twitch. Twitch Dual Format carries both orientations over a single stream key with nothing to configure in the Twitch dashboard, so the whole decision sits on the sending side. On YouTube, part of the setup lives in YouTube Studio and has to be done before a vertical feed can be accepted at all.
YouTube Dual Stream compared to Twitch Dual Format
Both give viewers a horizontal and a vertical version of one broadcast. They differ in where the configuration lives and how much control you get over the vertical picture.
| YouTube Dual Stream | Twitch Dual Format | |
|---|---|---|
| Stream keys | One for Auto, two for Encoder | One key carries both |
| Platform-side setup | Enable Dual stream in YouTube Studio | None required |
| Platform-generated vertical | Yes, the Auto option | Not offered |
| Bring your own vertical feed | Yes, with Encoder | Yes |
| Where the vertical is watched | Among YouTube Shorts | Twitch mobile app |
| Main friction | Choosing Auto or configuring two Encoder inputs | Producing the vertical picture yourself |
Neither approach is strictly better. YouTube's Auto option is the fastest way to get a vertical version at all, and it costs you nothing in upload. Twitch's single key is simpler to wire up but gives you no platform-side fallback if you cannot produce a vertical feed.
Three ways to produce the vertical picture
The horizontal side is settled. The real question in any dual format workflow is where the 9:16 video comes from, and there are three answers.
YouTube generates it (Auto)
YouTube derives the vertical version from your horizontal feed on its side. Nothing changes in your encoder and you only upload one stream.
Limitation: The picture is derived from the horizontal composition. Use the vertical layout controls, then check for cropped overlays and small text.
Your encoder produces it
You build a dedicated 9:16 scene locally and send it to the vertical stream key. Full control over layout, and the vertical scene can be composed for mobile from the start.
Limitation: You encode and upload two streams from one machine, which roughly doubles both encoding work and upload bandwidth. It also means running and switching a second scene while you are live.
A streaming server produces it
You upload one feed to a server, which builds the 9:16 version and delivers both stream keys. Local encoding and upload stay close to a single stream.
Limitation: It adds a hop between you and YouTube, and it is a paid service rather than something already included with your encoder.
What to watch out for
Most dual stream problems are not encoding problems. They are setup and framing problems that only show up once someone opens the broadcast on a phone.
Match the keys in Encoder mode
Send each orientation to its matching key. Check both previews before going live.
Configure vertical before starting
You cannot add the vertical format after the broadcast has started.
Vertical layout is a design decision
A full-height 9:16 crop of a 16:9 scene retains about a third of its width. Overlays, alerts, and text sized for desktop are frequently unreadable or cropped on the vertical version.
Bandwidth is the usual blocker
Producing both orientations locally means uploading both. On a mobile connection or a capped home upload, that headroom often is not there.
It is a YouTube feature only
Dual Stream affects the YouTube broadcast. Reaching Twitch, Kick, TikTok, or Instagram at the same time is a separate multistreaming problem.
How Streamrun fits into this
Streamrun is a cloud streaming engine, so it sits between your encoder and YouTube. You send one upload, Streamrun builds the vertical version, and both stream keys are delivered from the cloud rather than from your machine. Your local encoding and upload stay at roughly the level of a single stream.
- An Output stream element of type YouTube Dual Stream sends both stream keys from one configuration
- The vertical version can be generated automatically with subject tracking, or composed by hand on a custom vertical canvas
- The same vertical feed can go to TikTok, Instagram, and Twitch at the same time, without a second upload
- Disconnect protection keeps the broadcast alive when your connection drops mid-stream
For Streamrun, select Encoder in YouTube Studio and configure both keys before going live. The YouTube Dual Stream setup guide walks through the YouTube Studio settings and the Streamrun configuration.
Fix or turn off the vertical stream
Frequently asked questions
What is YouTube Dual Stream?
YouTube Dual Stream is a live streaming mode that publishes a horizontal 16:9 version and a vertical 9:16 version of the same broadcast at the same time. Desktop and TV viewers watch the horizontal version, and viewers in the YouTube mobile app can watch the vertical one. Both belong to a single live broadcast rather than two separate streams.
Does YouTube Dual Stream need two stream keys?
Only in Encoder mode. Auto creates vertical video from your horizontal input. Encoder takes a separate vertical input with its own key.
What is the difference between Auto and Encoder for the vertical stream?
Auto uses your horizontal input. Encoder lets you supply a separately composed vertical picture, giving you control over framing, layout, and overlays.
How is YouTube Dual Stream different from Twitch Dual Format?
Twitch carries both orientations on one key. YouTube offers Auto or a separate vertical key in Encoder mode.
Do I need two encoders or two devices for YouTube Dual Stream?
No. Auto needs one horizontal input. For Encoder mode, one machine can produce both outputs, or Streamrun can generate them from your single upload.
How much upload bandwidth does YouTube Dual Stream need?
If you produce both orientations locally, you upload both, so budget for the sum of the two bitrates plus headroom. If the vertical version is generated off your machine, you upload one feed and the second output is sent from there instead. On a mobile or capped connection, that difference is often what decides whether dual format is practical at all.
Can the same vertical output go to TikTok or Instagram as well?
Yes, if the vertical version exists as a real 9:16 video output rather than a crop YouTube applies on its own side. A vertical feed produced by your encoder or by a streaming server can be sent to YouTube alongside TikTok, Instagram, or a vertical Twitch output at the same time.
Related
What Is Dual Format Streaming?
The wider picture of horizontal and vertical streaming across platforms.
How to Stream Vertical on Twitch
The Twitch side of the same problem, and how Dual Format works there.
Automatic Vertical Framing
How a 9:16 version is generated from your main feed instead of built by hand.
YouTube Dual Stream Setup Guide
Step by step, from enabling Dual stream in YouTube Studio to going live.
One upload, both orientations
Send a single feed to Streamrun and let the cloud produce the vertical version and deliver both YouTube stream keys, without doubling your encoder load or your upload.