As an iOS developer, keeping up with the latest technologies is vital to create innovative applications that meet users' growing expectations. Dolby Vision, a type of High Dynamic Range (HDR) video, provides superior visual experiences with brighter highlights, richer colors, and deeper black levels. This article is a reference guide to incorporating Dolby Vision into your iOS apps, pointing to relevant sections in Apple's guide: "Incorporating HDR video with Dolby Vision into your apps".

Dolby Vision Capture on iOS

The ability to record Dolby Vision video is available on iPhone 12 and later models, provided they run on iOS 14.1 or higher. The Dolby Vision profile used in these devices is 8.4, which is cross-compatible with the Hybrid Log-Gamma (HLG) format.

When recording Dolby Vision, the device does more than just capture the image. It also generates Dolby Vision metadata. This metadata, utilized during playback on Dolby Vision-enabled devices, ensures the most accurate reproduction of the original content, considering the capabilities of the specific display it's being played on.

As an iOS developer, if you aim to configure your application to support Dolby Vision recording, it's important to understand the key parameters defining this workflow. The following section outlines the parameters required to set up Dolby Vision video capture within your iOS app.

Device and Format Compatibility

Start by checking if the AVCaptureDevice supports any format that includes the HLG_BT2020 color space. You can do this by determining if the supportedColorSpace for a given device format contains AVCaptureColorSpace.HLG_BT2020.

Setting up AVCaptureDevice

After confirming format compatibility, you will need to set up the activeFormat and activeColorSpace parameters for the AVCaptureDevice:

• activeFormat should be set to the format that supports the HLG_2020 color space (as discovered in the previous step).
• activeColorSpace should be set to .HLG_BT2020.

Configuring AVCaptureSession

The AVCaptureSession should be configured to use input priority. Set the sessionPreset parameter to .inputPriority.

Setting up VTCompressionSession properties

Next, you will need to configure the properties of VTCompressionSession. This includes setting the following parameters:

• kVTCompressionPropertyKey_ProfileLevel set to kVTProfileLevel_HEVC_Main10_AutoLevel
• kVTCompressionPropertyKey_TransferFunction set to kCVImageBufferTransferFunction_ITU_R_2100_HLG
• kVTCompressionPropertyKey_ColorPrimaries set to kCVImageBufferColorPrimaries_ITU_R_2020
• kVTCompressionPropertyKey_YCbCrMatrix set to kCVImageBufferYCbCrMatrix_ITU_R_2020
• kVTCompressionPropertyKey_HDRMetadataInsertionMode set to kVTHDRMetadataInsertionMode_Auto

Configuring AVAssetWriter

Finally, you'll need to configure the AVAssetWriter. The details of this configuration can be found in the "Exporting HDR Video" section in Apple's guide.

Dolby Vision Editing and Preview

Having the possibility of capturing the Dolby Vision content, you will want to offer your users the ability to edit the video and preview the applied changes in real-time. In this case, it's essential to properly manage Dolby Vision metadata depending on the operations your app makes. Refer to the "Previewing and Editing HDR Video" section in Apple's guide to learn the necessary steps to ensure the edited video meets the Dolby requirements. Additionally, you can explore this topic more by watching Apple's WWDC session: Edit and play back HDR video with AVFoundation

Note that besides ensuring the correct processing of the video image itself, you need to accommodate the graphic layer overlay on this content. This means all texts, stickers, effects, filters, etc., must be rendered in HDR. Otherwise, the colors of these elements won't align with the design intentions (e.g., some graphics can be darker or washed out), which will undoubtedly negatively impact the end-user experience.

Exporting Dolby Vision or SDR (derived from Dolby Vision)

Once Dolby Vision content is ready to share, the next step is correctly exporting it. For this, check the "Exporting HDR Video" section in Apple's guide, which provides the necessary steps to ensure your Dolby Vision content remains compatible with Dolby requirements.

When the target device or platform does not support Dolby Vision, you may need to convert Dolby Vision content to Standard Dynamic Range (SDR). Tone mapping is essential for correctly converting brightness levels and colors (between different color spaces), allowing for proper display of content on older devices that do not support Dolby Vision technology. Refer to the "Converting HDR Video to SDR Video" section in Apple's guide for a detailed walkthrough.

Dolby Vision Playback

Finally, when it comes to delivering the best viewing experiences, it's crucial to understand how to correctly playback Dolby Vision content on your apps. Apple provides details for this in the "Playing Back HDR Video" section of the guide.

How to confirm whether the application correctly handles the Dolby Vision content?

You may be wondering how to confirm whether the changes you made to adapt the application for Dolby Vision support are functioning correctly. We have prepared a guide that will assist you in verifying the processed Dolby Vision content. Check out this article to learn more.