The static function RTCRtpSender.getCapabilities() returns an RTCRtpCapabilities object describing the codecs and capabilities supported by the RTCRtpSender.

You can, similarly, obtain the capabilities of RTCRtpReceivers by calling the static function RTCRtpReceiver.getCapabilities().

kind

A string indicating the type of media for which you wish to get the sender's capability to receive. All browsers support the primary media kinds: audio and video.

An RTCRtpCapabilities object stating what capabilities the browser has for sending the specified media kind over an RTCPeerConnection. If the browser doesn't have any support for the given media kind, the returned value is null.

As a static function, this is always called using the form:

capabilities = RTCRtpSender.getCapabilities("audio");

The returned set of capabilities is the most optimistic possible list. It is entirely possible that certain combinations of options may fail to work when you actually try to use them.

Calling RTCRtpSender.getCapabilities() doesn't prime the browser in any way to handle media. Nothing is loaded, fetched, or otherwise prepared. It's a means of determining what might be usable before starting to try to access media.

Because the set of capabilities available tend to be stable for a length of time (people don't install and uninstall codecs and the like very often), the media capabilities can in whole or in part provide a cross-origin method for identifying a user. For that reason, in privacy-sensitive contexts, the browser may choose to obscure the capabilities; this might be done, for example, by leaving out rarely-used codec configurations.

The function below returns a Boolean indicating whether or not the device supports sending H.264 video on an RTCRtpSender.

function canSendH264() {
  let capabilities = RTCRtpSender.getCapabilities("video");

  capabilities.codecs.forEach((codec) => {
    if (codec.mimeType === "video/H264") {
      return true;
    }
  });
  return false;
}