AVMutableComposition + HTTP/2 Audio Dropout — iOS 26 Regression

When a streaming AVURLAsset served over HTTP/2 is wrapped in an AVMutableComposition, the audio silently drops out on iOS 26. The same file over HTTP/1.1 works. Playing the same HTTP/2 URL directly (no composition) also works. No errors are reported. Occurs on iOS and iPadOS physical devices — does not reproduce on Simulator or macOS.

Trigger

HTTP/2 + AVMutableComposition. CDN vendor doesn't matter.

• HTTP/2 + Composition → ❌ Audio silent
• HTTP/1.1 + Composition → ✅ Works
• HTTP/2 + Direct (no composition) → ✅ Works
• Download first, then compose locally → ✅ Works

Steps to Reproduce

1. Run on an iOS 26 physical device (not Simulator).
2. Select "Composition (streaming)", tap "Load & Play".
3. Video plays, then audio goes silent.
4. Select "Direct" — audio works.
5. Select "Composition (download first)" — audio works (same bytes, local file).

Environment

• iOS 26.0 / 26.1 / 26.4.2 — Xcode 26.4.1
• iPhone 15 Pro, iPad M2 9.7"
• Works correctly on iOS 18.x with identical code and URLs