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3. Pre- and Post-Processing

This section provides guidance on pre- and post-processing of video streams.

Unless specified otherwise by the Session Description Protocol (SDP) or codec, the color space SHOULD be sRGB [SRGB]. For clarity, this is the color space indicated by codepoint 1 from "ColourPrimaries" as defined in [IEC23001-8].

Unless specified otherwise by the SDP or codec, the video scan pattern for video codecs is Y'CbCr 4:2:0.

3.1. Camera-Source Video​

This document imposes no normative requirements on camera capture; however, implementors are encouraged to take advantage of the following features, if feasible for their platform:

  • Automatic focus, if applicable for the camera in use

  • Automatic white balance

  • Automatic light-level control

  • Dynamic frame rate for video capture based on actual encoding in use (e.g., if encoding at 15 fps due to bandwidth constraints, low light conditions, or application settings, the camera will ideally capture at 15 fps rather than a higher rate).

3.2. Screen-Source Video​

If the video source is some portion of a computer screen (e.g., desktop or application sharing), then the considerations in this section also apply.

Because screen-sourced video can change resolution (due to, e.g., window resizing and similar operations), WebRTC-video recipients MUST be prepared to handle midstream resolution changes in a way that preserves their utility. Precise handling (e.g., resizing the element a video is rendered in versus scaling down the received stream; decisions around letter/pillarboxing) is left to the discretion of the application.

Note that the default video-scan format (Y'CbCr 4:2:0) is known to be less than optimal for the representation of screen content produced by most systems in use at the time of this document's writing, which generally use RGB with at least 24 bits per sample. In the future, it may be advisable to use video codecs optimized for screen content for the representation of this type of content.

Additionally, attention is drawn to the requirements in Section 5.2 of [WebRTC-SEC-ARCH] and the considerations in Section 4.1.1. of [WebRTC-SEC].

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