About video codecs supported in OpenTok
The OpenTok platform leverages the WebRTC protocol and the real-time video codecs that are supported by WebRTC. In particular the OpenTok platform supports the VP8 and the H.264 video codecs. You can select which video codec you want to assign as your preferred codec for a particular OpenTok project.
Across the broad ecosystem of devices and browsers that OpenTok supports there are varying levels of support for the VP8 and H.264 real-time video codecs. Some endpoints support both video codecs, and some just support one video codec. Depending on the type of application you are building and the types of browsers and devices your end users will use, your choice of preferred codec will change.
A video codec has two parts, an encoder and a decoder. It has the ability to encode (compress) incoming digital video frames from a webcam into a stream of binary data that can be sent over a network. It also has the ability to ingest a stream of binary data and decode (decompress) it into a flow of raw video frames that can be displayed on a screen. The mechanism for encoding and decoding the video is the codec standard and for the purpose of this page we are going to talk about two popular ones, VP8 and H.264.
The VP8 real-time video codec is a software codec. It can work well at lower bitrates and is a mature video codec in the context of WebRTC. As a software codec it can be instantiated as many times as is needed by the application within the limits of memory and CPU. The VP8 codec supports the OpenTok Scalable Video feature, which means it works well in large sessions with supported browsers and devices.
The H.264 real-time video codec is available in both hardware and software forms depending on the device. It is a relatively new codec in the context of WebRTC although it has a long history for streaming movies and video clips over the internet. Hardware codec support means that the core CPU of the device doesn’t have to work as hard to process the video, resulting in reduced CPU load. The number of hardware instances is device-dependent with iOS having the best support. Given that H.264 is a new codec for WebRTC and each device may have a different implementation, the quality can vary. As such, H.264 may not perform as well at lower bit-rates when compared to VP8. H.264 is not well suited to large sessions since it does not support the OpenTok Scalable Video feature.
You can set the preferred video codec for a project on the Project page of your TokBox Account.
In routed sessions (sessions that use the OpenTok Media Router), the preferred video codec is used for all clients in the session.
In relayed sessions , clients send streams directly to one another, and each publishing-subscribing pair tries to find a common video codec that they can both use. In this regard, the video codec used by the pair may be different to the preferred video codec setting.
The following tables list the real-time video codec capabilities of the supported OpenTok endpoints. Note that almost all devices have H.264 decoder support for streamed movies, however the tables below are focused on the real-time video codec (encode and decode) capabilities of the devices.
|Internet Explorer (Plugin)||Yes||Yes|
|Chrome on Android||Yes||Partial 1|
|Firefox on Android||Yes||Yes|
|Chrome/Firefox on iOS 2||-||-|
|1 Chrome on Android only supports H.264 on devices that contain the Qualcomm and Exynos chipsets and require Chrome 65 or higher|
|2 Non-Safari browsers running in iOS (for example, Chrome and Firefox) use a Safari webview under the hood. The Safari webview does not support WebRTC and the OpenTok SDK.|
|iOS SDK (2.12+)||Yes||Yes|
|Android SDK (2.13+)||Yes||Yes for most devices *|
|Windows SDK (2.13+)||Yes||Yes|
|macOS SDK (beta)||Yes||No|
|* Hardware H.264 is supported on devices that contain the Qualcomm and Exynos chipsets, in addition to a subset of HiSilicon and MediaTek chipsets. Fallback to software H.264 is supported on Android M or higher.|
* Percentage of Android devices that support the codec
The main interoperability conflict is around Safari and Android devices. VP8 works on all Android devices, both on Android Chrome and the OpenTok Android SDK. Safari mobile and desktop do not have VP8 codec support. In contrast, Safari has H.264 codec support whereas H.264 codec support on Android is not ubiquitous.
In OpenTok Routed sessions, the preferred video codec set in the Project settings is used for all clients in the session. In OpenTok Relayed sessions, clients send streams directly to one another, and each publishing-subscribing pair tries to find a common video codec that they can both use. In this regard, the video codec used by the pair may be different to the preferred video codec setting.
Both H.264 and VP8 can work well for endpoints in small sessions (for example, 1-3 participants). However, since there is no Scalable Video support with H.264, we do not recommend H.264 for large sessions.
Since the same VP8 video codec implementation is used on almost all endpoints the quality is roughly the same. VP8 works well at lower bitrates. In addition, OpenTok Scalable Video is available with VP8. Scalable Video significantly improves the video quality in larger sessions.
The quality of H.264 will vary across devices since the implementation of H.264 varies. In addition we have encountered differences in quality depending on the operating system version running on the device. The quality of H.264 at lower bitrates is generally not as good as VP8.
H.264 works well on iOS devices since they have good support for H.264 hardware acceleration. This reduces the CPU load and improves battery life.
Here are the recommended video codec to use in some example scenarios:
In OpenTok Sessions with 2-3 participants where interoperability with the Safari browser is critical, use the H.264 video codec to ensure interoperability with Safari.
In OpenTok Sessions with 2-3 participants where only iOS devices are involved, use the H.264 video codec to take advantage of the hardware acceleration.
Webinars and Large Classroom sessions should use the VP8 codec to take advantage of the OpenTok Scalable Video feature.
In OpenTok Sessions where support for all Android devices is critical, use the VP8 codec.