What is the Optimal Bitrate for Your Resolution?

Thu, Dec 15, 2016
Bitrates and resolitions

 

We get a lot of questions about how to find the optimal resolution to bitrate ratio, and the truth is there really is no right or wrong answer. Depending on your encoder, streaming platform and audience, your resolution and bitrate will very likely be different, and because not everybody has the highest quality computer, there won’t be a bitrate that can work for every single viewer. That being said, the best thing you can do is optimize the ratio to have it viewable for the majority of your audience. Here’s how you can understand what the best bitrate for your stream is.

What Are Resolutions? What Are Bitrates?

To best determine the optimal ratio for your stream, let’s first define what resolutions and bitrates are and how they affect video quality and file size.

Different bitrates for different resolutions

A resolution is the number of pixels spread across a monitor screen, and is usually written in horizontal x vertical. The resolution of your monitor has a huge effect on the type of stream you are able to watch.

For example, if you have a 720p monitor and are watching a 720p stream, perfect. Your monitor can display every pixel of the video. If the stream was broadcast in 1080p, however, your monitor will compress the image into 720p due to its lack of 360 pixels. It won’t inhibit the video quality, but since the monitor can only see 720 pixels, anything beyond that is wasted bandwidth.

Bitrates graph

A bitrate is the amount of data required to encode a single second of video. From a streaming perspective, the higher the bitrate, the higher the quality, and the more bandwidth it will require. So why doesn’t everyone just upload at the highest bitrate possible? Well, not every viewer can download at the highest bitrate possible.

If you have a download speed of 5 Mbps and you are watching a stream at 6 Mbps, your computer will compress the file, the resulting video will be choppy and you’ll probably get stuck in buffering limbo. Most platforms nowadays though will transcode the video so that different connections have personalized bitrates, but this will often sacrifice quality. 

Bitrates aren’t always restricted to this straightforward definition. There are two different types of bitrates available: constant and variable.

What is Constant Bitrate (CBR)?

Constant bitrate vs variable bitrate graph

Exactly as it sounds, a constant bitrate spits out data at the same rate all throughout the video, and in streaming this means that viewers will receive data at the same rate. The problem with constant bitrates is that, unless the stream is just a static image, video segments will change. Some segments will have more detail and some have less detail. This translates to lower quality during complex segments and unused bandwidth on simple segments. Some situations will still use constant bitrates, but these instances are rare.

What is Variable Bitrate (VBR)?

Variable bitrates are the data transfer process of choice for the majority of circumstances, because encoders will adapt to the detail demand of the segment. It essentially allocates more data during complex segments, and less data during simple segments. For instance, if your stream has a segment of you standing in front of a plain white background, the encoder will determine that the video needs less data and transfer less. If you streamed at a concert, the encoder will see varying details and transfer more data when needed.

So What Bitrate Should I Use?

The bitrate that you choose will largely depend on the speed of your connection. With an upload speed of 10 Mbps, you could of course upload up to that amount, but this will hinder the rest of your Internet connection. Also, bear in mind the target audience you are broadcasting to, and speculate what type of connections and devices they are watching on. A viewer watching a church sermon and a viewer watching an e-sports tournament will have very different setups.

So while there isn’t exactly a golden ratio, here is what we generally recommend for streaming:

1080p : 4Mbps to 6Mbps

720p:    2Mbps to 4Mbps

480p:    1Mbps to 2Mbps

360p:    400kbps   to 1.5Mbps

240p:    300kbps   to 700kbps

If you happen to be using Teradek’s VidiU to stream, your VidiU portal comes with a couple of preconfigured settings for video quality: Full HD, HD, High, Medium, Low, Mobile. Here are the specs for these settings:

Full HD: 1920 x 1080 / 5.2 Mbps

HD:        1280 x 720  / 2.2 Mbps

High:      960 x 540 / 1.4 Mbps

Medium: 736 x 414 / 796 Kbps

Low:       480 x 270 / 446 Kbps

Mobile:   360 x 200 / 273 Kbps

Keep in mind that every streaming platform comes with different presets which may or may not limit the amount of bitrates you are allowed to transfer. Here are all of the popular streaming destinations and their settings:

Ustream:

https://support.ustream.tv/hc/en-us/articles/207852117-Internet-connection-and-recommended-encoding-settings

Facebook Live: (1080p not allowed)

https://www.facebook.com/facebookmedia/get-started/live#live-video-specs

Youtube:

https://support.google.com/youtube/answer/1722171?hl=en

Youtube codecs can stream far better quality, hence the higher limits.

Twitch:

https://help.twitch.tv/customer/portal/articles/1262922-open-broadcaster-software

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