fix: handle av1 VideoDecoder errors

[matthew-hre]

Description

Fix AV1 VideoDecoder error during export when recordings use AV1 in WebM containers (the default on Linux). When web-demuxer returns a bare "av01" codec string, we now parse the AV1CodecConfigurationRecord from the extradata to build the full WebCodecs-compatible codec string (e.g. "av01.0.09M.08").

Motivation

My export kept crashing 😭. Chrome/Electron's MediaRecorder writes AV1 WebM files with an AV1CodecConfigurationRecord whose version field is 127 (0xFF first byte) instead of the spec-mandated 1 (0x81). The web-demuxer library's WASM-side parser (set_av1_codec_string) strictly checks version != 1 and bails early, returning a bare "av01" string rather than the full parametrized form. VideoDecoder.configure() then rejects it with "Unknown or ambiguous codec name", making all AV1 exports fail.

extradata: FF 09 0C 00
               ↓
web-demuxer: version = 0xFF & 0x7F = 127 ≠ 1 → early return → "av01"
               ↓
VideoDecoder.configure({ codec: "av01" }) → "Unknown or ambiguous codec name"

When getDecoderConfig() returns a bare "av01", we now parse the extradata ourselves, only requiring the marker bit to be set rather than a strict version check. For the example above this produces "av01.0.09M.08" (Main profile, level 3.1, Main tier, 8-bit). Falls back to "av01.0.01M.08" if extradata is missing or too short.

Type of Change

• New Feature
• Bug Fix
• Refactor / Code Cleanup
• Documentation Update
• Other (please specify)

Related Issue(s)

None. Discovered while packaging for NixOS.

Screenshots / Video

N/A: no UI changes. The fix is in the export pipeline (streamingDecoder.ts).

Testing

1. Record a screen capture on Linux (records AV1 in WebM by default)
2. Open the recording in the editor
3. Click Export

Before fix: Export fails with "VideoDecoder Error: Unknown or ambiguous codec name"
After fix: Export completes successfully

You can verify your recording is AV1/WebM with:
ffprobe -v warning -select_streams v:0 -show_entries stream=codec_name ~/.config/openscreen/recordings/<your-recording>.webm

If you see Unknown version 127 of AV1CodecConfigurationRecord found! in the warnings, your file is affected by this bug.

Checklist

• I have performed a self-review of my code.
• I have added any necessary screenshots or videos.
• I have linked related issue(s) and updated the changelog if applicable.

Summary by CodeRabbit

• Bug Fixes
  • Improved AV1 codec detection and normalization so players now recognize generic AV1 labels and use a precise codec string when available, improving compatibility and playback reliability for AV1-encoded video.