Video

This document aims to outline what is being done to your content and the different knobs you can tweak to get the best output for your instance.

Overview

  1. Configure your broadcasting software to send a stream to Owncast that is reasonably close to what you expect to send to your viewers. How you configure your broadcasting software matters. Don’t tell OBS to send to Owncast at 7000k at 60fps if you only expect to support bitrates of 4000k and 2000k at 30fps.
  2. Start with a single output configuration with average settings. Test it. See how your hardware handles it. If you want to, and are able to, then add another and test that. Repeat until you arrive at the configuration you want to offer your viewers and that your hardware can handle.
  3. If your hardware can’t handle your current configuration then reduce the number of output variants to only a single one, reduce the quality of video you’re sending to Owncast, reduce your framerate, and reduce the CPU usage

Your stream can be played outside of your web site.

Because Owncast uses the HLS standard, almost any video player can play your stream. Quicktime, VLC, mpv, etc. You could even build your own app that plays it. You can access your stream directly on your server by putting the path of /hls/stream.m3u8 into your player. For example: https://owncast.mydomain.com/hls/stream.m3u8.

How does an Owncast video stream work?

Owncast takes your source stream and converts it to short, individual video segments. A list of these segments is supplied to your viewer’s player and will read and play all the segments in order. This is using a specification called HLS or HTTP Live Streaming. You can optionally generate multiple different qualities of video to allow lower bandwidth options. This is called Adaptive bitrate streaming.

This video from Jon Dahl is gives a very good overview of internet video, starting with “what happens when you press play in your web browser?" and touching on every piece of the stack, backend and frontend. It translates very well to how Owncast works and is suggested if you want to learn more.

In this case Owncast works as the Media encoder, Stream segmenter, and distribution web server. However Owncast supports video being distributed via 3rd party storage as well, so in that case the video segments would be distributed from there, instead.

Things to keep in mind.

  1. The more work you need done to convert the video from one size, quality or format to another the more it will slow everything else down.
  2. The slower things go the slower the stream is provided to the user.
  3. If stream is provided to the user too slowly they’ll start seeing buffering and errors.

Here’s what knobs can be tweaked when trying to determine the quality or qualities you want to provide your user while balancing the amount of server resources you’re consuming.

Things you can configure

Bitrate

The bitrate is the amount of data you send when you stream. A higher bitrate takes up more available internet bandwidth and create larger sized segments of video, making it take longer for viewers to download. Increasing your bitrate can improve your video quality, but only up to a certain point.

Resolution

Resolution refers to the size of a video on a screen. Like bitrates you can provide multiple different sizes for different cases, but asking to resize a video amounts in additional work that needs to be performed.

It’s recommended if you have to change the size to only change the width or the height, and it’ll keep the correct aspect ratio for you. If you change both the width and the height you may be changing the aspect ratio of the video you may end up with a squished picture if you don’t set it correctly.

Framerate

Framerate is the number of frames per second in the video. Owncast defaults to 24fps, but other common framerates are 30 or 60. Increasing the framerate will use more CPU on your server, and more bandwidth for your users as more frames of video have to be processed and made available to your viewers any given second.

CPU Usage

The more CPU you use the better the output image will be, or the smaller of a file the output will be for the same quality. However, you will need to balance the amount of CPU you have available with the amount you can use to process video.

Latency Buffer

You have some control over the live latency between the broadcaster and the viewer. While it’s completely understandable to want to have as little latency as possible you may need to increase the latency buffer if you’re experiencing issues. In general the lower the latency the less buffer is available for any possible slow transfers, network blips or errors.

Video Passthrough

Owncast has an optional setting to turn off re-encoding of your inbound stream, potentially saving substantial hardware utilization and supporting a higher quality stream with less resources. However, because your video will not be re-encoded it’s possible that certain video from certain sources may end up not being playable at all. This is the risk of enabling this.

To enable, visit the advanced settings for a specific stream output. You can turn on “Video Passthrough”.

  1. Turn it on if you require it.
  2. Test it.
  3. If your video won’t play, then turn it off.
  4. Only one output should be set as “passthrough”.

If you find you require this feature, but it’s not working for you, you may be able to change to a different broadcasting client solution to send video to Owncast differently. For example, if you’re using Restream, video passthrough will not work, but in general it’s worked for people streaming from OBS.

Audio

What you’re sending from your broadcasting software is generally reasonable and additional conversion isn’t required, even for low-bandwidth viewers. Owncast will not change the audio stream and instead just pass it along to the end users to save additional work being performed.

How you configure your broadcasting software matters.

The more you send to Owncast, the more work it has do. This means you should generally not stream to Owncast at a significantly higher or lower quality than you expect to give to your viewers. It makes no sense to stream to Owncast at 6000k 60fps if you’re telling Owncast to send to your viewers at 3000k 30fps, because your server has to do that conversion. On the other hand it makes no sense to stream to Owncast with a 1000k bitrate and then send to your viewers at 4000k, that would be wasted work and bandwidth.

So in short: Try to reasonably figure out what you want to stream to your users and match that as best as possible when setting up your broadcasting software.

If you find yourself trying to squeeze better performance out of Owncast then try setting your broadcasting software to a lower quality as well as lowering the quality in your Owncast instance.

CPU Usage

Each stream output variant adds significant CPU usage and slows down the overall generation of video segments. If you have a slow server running Owncast you should probably only have one bitrate variant in play. If you add more and you notice that playback becomes choppy it’s likely that everything is running too slowly for consistent playback. Consider removing the additional variants and tweaking your single variant so it supports a wider variety of network conditions.

Disk Usage

More stream output variants requires more disk space, since it’s another copy of the video on disk. If you’re serving video locally and you have enough disk space then it’s probably no big deal and files will rather quickly get rotated and cleaned up. If you’re using something like S3 for storage then files won’t get cleaned up until some point in the future, so you’ll have more remote storage use in play.