Scaling applications to support large real-time calls
Daily defines large meetings as real-time calls with 50 to 15,000 participants, and even larger sizes when the call is being live streamed. All large calls need to route hundreds to thousands of participant media tracks at a time, which means there's a quite a bit of room for optimizing calls through Daily configurations, as well as app UI considerations.
This guide covers the Daily recommended settings for few-to-many calls, including Daily's 15,000 participant interactive live streaming. We'll also review best practices to scale large calls in terms of interacting with the Daily APIs and recommended app-level decisions.
There are three main categories of large calls to consider when building your Daily app or choosing your room configurations:
- Large real-time calls where everyone (up to 300 participants) are active, meaning anyone in the call can turn on their devices. This is possible in custom Daily apps and apps using Daily Prebuilt.
- Interactive live streaming of up to 15,000 participants: Up to ten active participants can join with their devices on in a call and up to 15,000 participants can join the call in real-time. This is a type of "few-to-many" call setting available through Daily, which allows a group of speakers in a call and a large group of attendees.
- Live streaming: Stream your real-time call to grow your live viewership into the millions.
We'll take a look at these options below.
We'll also review additional ways to make your app more performant in our Best Practices section, including how to incorporate:
Daily classifies calls with up to 300 active participants as interactive large sessions. Conference breakout rooms or workshops, corporate trainings, and other virtual events where any participant may need to speak all fall under this category.
Platforms to support interactive large sessions can be built using either Daily Prebuilt or Daily's call object. In either case, core Daily features like recording, output to live streaming platforms, and transcription are all available.
Let's now take a look at the specific settings required to support calls of up to 300 participants in both Daily Prebuilt and custom ("call object") Daily apps.
To support large calls of over 50 participants and up to 300 participants, the
experimental_optimize_large_calls room configuration must be set to
experimental_optimize_large_calls room configuration will have several side effects in the Daily Prebuilt to help manage your call's performance with such a large number of participants:
- The local participant will be automatically muted on join. They can unmute as needed once they've joined a call.
- The grid view will show a maximum of 12 participants in the grid at a time, compared to the default of 25 and maximum of 49.
- Only 8 users can be unmuted at the same time. When more than 8 users are unmuted, the oldest active speaker will be automatically muted.
In addition to these room settings, Daily Prebuilt is built to optimize performance based on its layout options. With Daily Prebuilt, each participant can view the call with either of the following two views:
- Active speaker layout, where the person currently speaking takes up the majority of the screen.
- Grid view, a paginated grid layout with a subset of participants visible on screen.
In larger calls, grid view will automatically be paginated and active speaker mode will have a scrollable participant bar for the non-active participants. These features help avoid all media tracks being rendered at the same time.
These calls can support up to 300 participants with all cameras on, with each participant viewing (and receiving tracks from) at most ten other participants at a time.
To optimize performance of custom apps hosting large calls, read our Best Practices section below.
Interactive live streaming is a "few-to-many" type of call available through Daily's APIs. It refers to calls where up to 10 participants can turn on devices and a total of 15,000 participants can watch the call in real-time.
Let's start by reviewing what types of use cases benefit from few-to-many calls and the different ways Daily APIs can support them. (Or jump to our Daily Prebuilt or custom implementation sections on how to configure Daily rooms/domains to use interactive live streaming.)
Keynotes, panels, and webinars are examples of "few-to-many" calls where some call participants speak but most are listening to the presentation. In other words, they involve a few speakers addressing many attendees. The attendees are in a "listen-only" mode, which — from a video app perspective — means they are not able to turn on media devices, such as a local camera or microphone.
Few-to-many calls encompass several variations of app and Daily room configurations, including:
- Daily Prebuilt using the
owner_only_broadcastsetting only. This setting allows up to 10 speakers and 1,000 participants to join a call. (Learn more in our room settings guide.)
- Interactive live streaming: Host up to 15,000 participants with up to 10 speakers. This can be done with:
- Daily Prebuilt or custom apps using Daily live streaming to maximize viewership (more on that below).
Let's now focus on interactive live streaming, which acommodates the largest real-time call sizes.
Interactive live streaming is a type of few-to-many call. It allows up to 10 call participants to turn on their devices and up to 15,000 attendees to view the call in real-time.
Participants who can turn on their devices are considered "active" and participants who cannot turn on devices are considered "hidden".
Active participants are participants who have a "presence" in a call. They can turn on their devices during the call and have their participant information available in the
participants() method return value.
Hidden (or "passive") participants are considered to not have a "presence". They can view a real-time call but cannot turn on their devices and do not have their participant information returned by the
There are a few key numbers to be aware of when supporting calls of up to 15,000 participant with Daily:
- Daily calls transition into interactive live streaming when there are over 1,000 participants in the call. Use the room configurations listed below once you plan to have 1000+ participants in your call.
- At most ten participants can be active, meaning ten cameras and microphones can be on, as well as one screen share.
- All other participants must have cameras and microphones off.
- Every client will receive real-time video and audio, whether they're a speaker or attendee.
There are a few required room settings to support call sizes this large and create the active vs. hidden participant dynamic. Keep reading to learn about settings you'll need for Daily Prebuilt or custom apps.
To set up interactive live streaming with Daily Prebuilt, the following room and/or domain properties must be set to
Here is an example cURL command enabling these room properties:
To set up interactive live streaming session with a custom Daily app, the following room properties must be set to
Here is an example cURL command enabling these room properties:
To control who starts a call as a presenter and who starts as a viewer, consider using the
start_video_off meeting token properties.
- Presenters should have these properties set to
false, the default. This means their devices will start by being on.
- Viewers should have these properties set to
true, so their devices are off when they join the call.
You can also limit who can turn on devices via the
is_owner meeting token property, and only allow meeting owners to access their devices.
Balancing the number of total participants with the number of devices turned on is important for managing app performance. To host calls with more than 10 active participants (i.e. with devices on) and more than 300 total participants, contact our support team.
Daily sessions can be broadcast to multiple live streaming platforms, like AWS IVS or YouTube Live. Live streaming can be the best option for a large call if hundreds of thousands of people or more could be tuning in, or if providing a viewing link to attendees is preferred to managing silent participants on a call. For more details on Daily live streaming and how to implement it, head to the guide.
To learn more about customizing the layout of Daily live streams or adding custom graphics, read our guide on using Daily's Video Component System (VCS).
As the number of call participants increases, the number of audio, video, and screen media tracks that need to be routed and then handled by each web client multiplies. This can drain CPU, strain networks to their limits (risking undelivered media streams), and degrade user experience quickly, especially on older or mobile devices.
To optimize performance on calls with hundreds of participants, pagination, track subscriptions, and simulcast layer control can all be implemented using Daily’s APIs. Analyzing call logs can also help improve call quality.
Pagination limits the number of participants displayed on a screen at a time, so a call participant has to click to rotate through all other attendees. This reduces the load on any individual participant’s CPU and bandwidth.
The gif highlights a demo app built on React, but pagination can be implemented regardless of the framework used.
Use the Daily
participants() method to access the full list of active participants in a call. Once the participants are known, you can do the following to build out your pagination logic:
Establish constant UI elements like the minimum participant video tile width, default aspect ratio, and the maximum number of tiles per page.
Use the UI constants and the number of call participants to calculate the total number of pages. The number of pages, and which participants are on each page, should update as the number of call participants changes, so set up the state management of your choice.
Add click handlers to the pagination buttons that update the app state to reflect the current page being viewed.
Set up a handler to determine the visible participants on a given page, using the current page, number of participants, and maximum number of tiles per page to make a copy of the participants object that only includes visible participants.
Iterate over the visible participants object to render each participant in the UI.
Daily calls operate on a publish-subscribe model: participants publish audio, video, and screen MediaStreamTracks, and are subscribed to other participant’s tracks.
By default, Daily routes a participant’s distinct set of tracks to all the other participants on a call. In large calls with hundreds and thousands of participants, decoding all that video can demand a lot of network bandwidth and processing power.
Turning off Daily’s default track handling in favor of manual track subscriptions can deliver better call quality during sessions with many participants. Track subscriptions can also enable features like breakout groups, and improve features like pagination.
There are three steps to set up direct track subscriptions:
- Set the
subscribeToTracksAutomaticallycall object property to
This turns off Daily’s default track management. This property can be passed on
createCallObject(), or via the
setSubscribeToTracksAutomatically() method. The latter is a good option if you want to wait to turn on track subscriptions until a certain number of participants have joined the call.
updateParticipants()to change the
subscribedvalue of a participant's
Each individual participant’s
tracks property can be found on the Daily participants object.
tracks for a participant include
video (camera), and
screenVideo (screenshare) properties. Each track type contains: a raw media stream track object available on both
state of the track, and its
state indicates if the track can be played (full possible states in the participants() documentation).
subscribed tells us whether or not the local participant is receiving the track information from the participant who the track belongs to. Its value is
true if the local participant is receiving,
false if they are not, or
subscribed status of
"staged" keeps the connection for that track open, but stops any bytes from flowing across. Compared to a complete connection teardown through an unsubscribe, staging a track speeds up the process of showing or hiding participants' video and audio. Staging also cuts out the processing and bandwidth required for that track.
On calls with many participants, setting the
subscribed value to
false depending on the interface can minimize the load on participants’ connections, improving the user experience. Paginated grid apps (including Daily Prebuilt!) often subscribe to the tracks of participants on a current page, stage those on the previous and next pages, and unsubscribe from the rest.
updateParticipant() receives an object with the participant’s
id as the key, and the value a
setSubscribedTracks object indicating the new
subscribed status of each track type.
updateParticipants(), combine all participants’ updates into one object.
- Listen for participant events to reflect updated participant state in the app interface.
updateParticipant() method fires a corresponding
"participant-updated" event. Add a listener to this event to update the app interface as participants’
subscribed statuses change.
To take advantage of simulcast layers, the call must be happening over an SFU connection. To test over SFU in development, use the
setNetworkTopology() method. This is only for testing. In production, once a fifth participant joins a call — or if recording, transcription, or a live stream is started — an SFU connection will be automatically established.
Once a fifth participant joins a Daily call — or if recording, transcription, or a live stream is started — instead of direct peer-to-peer (P2P) connections, tracks are first sent to a Selective Forwarding Unit (SFU). From there, the SFU processes, re-encrypts, and routes media tracks to participants, allowing tracks to be "selectively" forwarded.
With WebRTC simulcast, instead of sending a single track to the SFU, a publishing participant’s web client sends the same source track at a few different resolutions, bitrates, and frame rates. Each of these groups of settings is known as a simulcast layer.
By default, the Daily client and SFU will work to send the highest layer possible.
There are several factors that affect which layer a participant receives. Those factors include:
- The available bandwidth on the receiving end: The SFU will send a lower layer if the current one exceeds the available bandwidth.
- The send-side is not sending all the layers: This typically occurs when the browser detects network or CPU issues or the highest video resolution of the device does not support the highest layers. It's also worth noting that the browser can and will modify the actual bitrate, frame rate, and resolution sent on each layer for these same reasons, so the actual settings used may not match the configuration.
|Layer 0||Layer 1||Layer 2|
|Frame rate (fps)||10||15||30|
|Resolution (width height)||320x180||640x360||1280x720|
|Layer 0||Layer 1|
|Frame rate (fps)||10||30|
|Resolution (width x height)||320x180||1280x720|
While the default Daily simulcast management suits most use cases, it is possible to adjust the quality of both the video a participant publishes to the server (send-side) and the video that participants receive (receive-side). This can be useful in large calls as a tool to optimize bandwidth, but proceed with caution. Attempting to make changes while calls are in progress or to use values beyond browsers' capacities can cause problems. Please reach out if we can help.
Adjusting the quality of the video that participants send to the server can be useful in large calls. For example, the main active speaker showcased prominently in the UI could send higher quality video than the other call participants.
There are two properties that can be manipulated to adjust send-side video quality:
maxBitrate: the desired video bitrate for the layer, in bits per second.
maxFramerate: an integer value lower than the maximum rate expected from the camera, in frames per second.
scaleResolutionDownBy: an integer power of 2. The horizontal and vertical dimensions of the source video will be divided by this number to get the resolution for the layer.
trackConstraints property, set via the
setBandwidth() method, determines the 'input quality' of the video that a browser gets from a web cam by defining a maximum resolution (
height values) and a
setBandwidth() call needs to happen before a video track is requested from the participant. Disable video on
join() for participants whose bandwidth constraints need to be set manually, then call
setBandwidth(), then enable the camera.
If many participant videos will be displayed or if they will be rendered on small mobile screens, for example, programmatically requesting a lower bitrate layer can improve call performance. Lower quality videos not only save downstream bandwidth, but also can dramatically improve CPU performance since they require fewer resources to render.
To use Daily receiveSettings to request a specific simulcast layer:
Listen for the
"receive-settings-updated"event to update the app interface in response.
See the logs and metrics guide for details on analyzing call quality.