[Webkit-unassigned] [Bug 281945] New: VideoEncoder.configure for H265 does not respect {hevc: {format: "annexb"}}

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=281945

            Bug ID: 281945
           Summary: VideoEncoder.configure for H265 does not respect
                    {hevc: {format: "annexb"}}
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: Unspecified
                OS: macOS 15
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Media
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: jacob at bandes-stor.ch

For H265 VideoEncoder, according to https://www.w3.org/TR/webcodecs-hevc-codec-registration/#videoencoderconfig-extensions, the AnnexB format is supposed to be requested with `{hevc: {format: "annexb"}}`. However, it seems like `{avc: {format: "annexb"}}` (the H264 version) is what actually works in Safari.


- Visit https://codesandbox.io/p/sandbox/dystmn?file=%2Fsrc%2Findex.mjs%3A45%2C32
- Open console
- Observe "output chunk" log messages with Uint8Array [0, 0, 0, 31, ...]  (not annex b format)
- Comment the `hevc: { format: "annexb" }` line and uncomment the `avc: { format: "annexb" }` line
- Observe the "output chunk" log messages change to Uint8Array [0, 0, 0, 1, ...] (annex b format)

The expected behavior would be that `{hevc: {format: "annexb"}}` should produce Annex B formatted data, according to https://www.w3.org/TR/webcodecs-hevc-codec-registration/#videoencoderconfig-extensions.

Tested with Safari 18.0.1 and STP Release 205 (Safari 18.0, WebKit 20621.1.2.111.4)

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