Ultra low latency streaming, down to sub-second playback.

Low latency streaming is live video delivered with a much shorter delay between the camera and the viewer than standard streaming. Ordinary HLS playback commonly runs 20 to 40 seconds behind live because video is packaged into segments and buffered by the player. Low latency video streaming shrinks or replaces those buffers so the stream plays seconds, or fractions of a second, behind the live moment.

Castr's documentation describes three playback tiers: the standard HLS player at about 35 seconds, the Low Latency player at under 15 seconds and around 7 in practice, and Sub-Second Streaming at under two seconds. These are documented figures rather than guarantees, since the delay you measure also depends on encoder settings, network path, and the viewer's device.

Start on the contribution side with a two-second keyframe interval, constant bitrate, and a zero-latency encoder tune, the settings Castr's docs recommend for sub-second streams. Then pick the playback tier: toggle the Low Latency player on an existing stream, or create a Sub-Second Stream when viewers need to react in real time. Delay you add deliberately, like an SRT latency buffer on a rough network, trades a little speed for stability.

LL-HLS, or Low-Latency HLS, extends HLS to deliver partial segments, cutting typical delay from tens of seconds to a few seconds while keeping HLS device reach and CDN-friendly scaling. WebRTC streams over a real-time peer connection and reaches sub-second delay, which suits interaction, but it needs a WebRTC-capable player. At Castr, the Low Latency player covers the few-seconds range and Sub-Second Streaming covers real-time playback, so you choose per stream.

SRT and RTMP ingest are included on all plans. The Low Latency player is included on Ultra and Events plans, and Sub-Second Streaming is an add-on on Premium plans and higher. Sub-second streams start with a default limit of 5 concurrent viewers and a watermark until the add-on is upgraded through sales. See Castr pricing for the full comparison.

The Sub-Second Streaming add-on is available from the Premium plan, and its pricing is custom: the sales team scopes it with you based on how many concurrent viewers you need and how much you stream. The default 5-viewer limit and the watermark are lifted as part of that conversation, so the add-on is sized to your event rather than a fixed tier.

Anything where the viewer acts on the stream: live auctions where a bid lands against a closing timer, sports betting where odds move with the play, live shopping, remote production confidence feeds, and interactive Q&A. If the audience only watches, a delay of half a minute is rarely noticed, and standard HLS scales more easily.

A Sub-Second Stream starts with a default limit of 5 concurrent viewers and a watermark on playback, which covers testing, confidence monitoring, and small bidding rooms. For a larger interactive audience, Castr's sales team upgrades the add-on and sizes the viewer limit to your event. When most of the audience only watches, pair the sub-second room with a standard HLS stream, which scales over multi-CDN delivery instead of a viewer limit.

No. Sub-Second Streaming plays through Castr's own player, embedded on your site or shared as a link. When the same broadcast goes to YouTube, Facebook, or other social destinations, those platforms deliver it at their own standard latency.

Yes. Castr’s video team will walk through your current setup, from sources and destinations to audience scale, security, and monetization, and confirm the fit before you migrate.