Comprehensive export pipeline fixes and improvements

[AIEraDev]

Summary

This PR addresses all critical, high, and medium-priority issues in the export pipeline, along with important low-priority improvements. All 1350 tests pass across 113 test files with zero TypeScript errors and clean Rust compilation.

Critical Fixes

C1: Blank PNG/Sequence Export

Problem: Single-frame PNG exports and sequence exports were producing blank output due to the same WebGL initialization race condition that affected video export.

Solution: Added waitForReady() calls to:

• exportFrame.ts - Single PNG frame export
• exportSequence.ts - PNG sequence export

Also cleaned up double-release pattern in exportFrame.ts to use finally block.

C2: Export Cancel Button Not Working

Problem: Cancel button in export dialog didn't actually kill the FFmpeg process. Module-level AbortController caused state pollution across export sessions.

Solution:

• Implemented onSessionReady callback pattern to pass live cancel() function to dialog
• Replaced module-level abort controller with session-scoped cancellation
• Cancel button now properly terminates FFmpeg process mid-export

C3: Module-Level AbortController State Pollution

Problem: Shared AbortController at module level caused cross-session contamination and export session leaks.

Solution: Replaced with onCancelReady callback for session-scoped cancellation in exportSequence.ts.

High Priority Fixes

H1: ProRes Preset Pixel Format

Problem: ProRes preset didn't map pixel_format to appropriate profile, limiting codec options.

Solution: Added pixel format to ProRes profile mapping in export.rs, enabling ProRes 4444/LT/HQ variants.

H2: u32 Arithmetic Overflow

Problem: Unchecked u32 subtraction and unbounded progress calculation could cause panics.

Solution:

• Hardened with saturating_sub
• Added progress.min(1.0) clamp

H3: H.265 IDR Frame Insertion

Problem: -force_key_frames expr: flag was incorrect for H.265/x265 encoder.

Solution: Replaced with -x265-params force-idr=1 for proper IDR frame insertion.

H4: Blocking ffprobe Call

Problem: has_audio_stream used synchronous std::process::Command, blocking Tokio runtime.

Solution: Made function async using tokio::process::Command.

H5: Double-Release Pattern

Problem: Manual cleanup before early returns in exportFrame.ts could skip cleanup on error paths.

Solution: Consolidated cleanup into finally block.

Medium Priority Improvements

M3: Array.from() OOM Risk

Problem: Converting large Uint8Array to JavaScript array via Array.from() could cause out-of-memory errors.

Solution: Switched to direct Uint8Array binary IPC.

M5: waitForReady Timeout

Problem: waitForReady() could hang indefinitely if GPU context never initializes.

Solution: Added 10-second timeout with descriptive error message.

M6: Redundant flushFrameBatch

Problem: Unnecessary flushFrameBatch() call after export loop.

Solution: Removed redundant call.

M7: Vec::remove(0) Performance

Problem: Ring buffer implemented with Vec::remove(0) was O(n) per operation.

Solution: Replaced with VecDeque::pop_front() for O(1) performance.

Low Priority Improvements

L4: Export Preset Duplication

Problem: Export preset definitions duplicated between ExportDialog and backend.

Solution: Created exportPresets.ts as single source of truth shared by both UI and backend.

L6: Partial File Cleanup on Cancel

Problem: If process.kill() failed in cancel_video_export, function returned early without cleaning up partial file.

Solution: Made kill operation non-fatal; partial file cleanup always runs.

Performance Improvements

• Video Seek Throttling: Increased readyState polling interval from 5ms to 50ms to mitigate WebKit's seek-suspension bottleneck and reduce CPU thrashing

Files Changed

• src/core/render/pixiSceneCompositor.ts - Added isReady/waitForReady with timeout
• src/lib/export/videoExport.ts - Await compositor + session-scoped cancellation
• src/lib/export/exportFrame.ts - Await compositor + finally cleanup
• src/lib/export/exportSequence.ts - Await compositor + onCancelReady callback
• src/components/ui/ExportDialog.tsx - onSessionReady callback pattern
• src/core/resources/VideoElementPool.ts - Seek throttling optimization
• src-tauri/src/commands/export.rs - All Rust improvements (HEVC tag, async ffprobe, ProRes, arithmetic hardening, IDR fix, ring buffer, cancel cleanup)
• src/lib/export/exportPresets.ts - New shared preset definitions

Testing

• ✅ All 1350 tests passed across 113 test files
• ✅ Zero TypeScript errors
• ✅ Clean Rust cargo check compilation
• ✅ No regressions detected

Next Steps

Real-world export testing recommended, especially:

• H.265/HEVC clips at 4K resolution
• ProRes exports with different profiles
• Export cancellation mid-process
• PNG sequence exports
• Single frame exports