Reuse a TimeCode instance in TimeSpanToDisplayFullConverter

[ivandrofly]

Summary

• Reuse a private TimeCode instance in TimeSpanToDisplayFullConverter.Convert instead of allocating a new one on every call
• Return cached string constants for the zero-time fallbacks
• Parse ConvertBack input with allocation-free Span.SplitAny instead of string.Split, collapsing the duplicated frame-mode/time-mode branches into one
• The converter runs for every visible time cell binding, so this trims steady-state GC pressure in the main grid

Benchmark: Convert

BenchmarkDotNet (ShortRun, .NET 10.0.10, X64 RyuJIT AVX2, i7-13700), mirroring the converter's old vs new formatting path:

Method	Mean	Allocated
Old: new TimeCode(ts).ToString()	33.76 ns	72 B
New: reused instance ToString()	31.26 ns	48 B
Old: new TimeCode(ts).ToHHMMSSFF()	35.13 ns	72 B
New: reused instance ToHHMMSSFF()	33.74 ns	48 B

The change removes the 24 B TimeCode allocation per call (the remaining 48 B is the result string itself); the time delta is minor. Note the converter is only used from Avalonia bindings on the UI thread, so the shared mutable instance is safe there.

Benchmark: ConvertBack

Same setup, old string.Split parsing vs the new span-based SplitAny:

Input	Old (string.Split)	New (SplitAny span)	Ratio	Alloc old → new
00:01:23,456 (ms mode)	53.4 ns	30.1 ns	0.56	208 B → 24 B
00:01:23,456 (frame mode)	54.2 ns	30.5 ns	0.56	208 B → 24 B
01:02:03.12	52.2 ns	29.2 ns	0.56	208 B → 24 B
not a time (invalid)	14.8 ns	8.9 ns	0.60	56 B → 24 B

~1.8× faster; the 184 B saved per call is the string[] plus the four substring allocations from Split. The remaining 24 B is the TimeSpan box forced by IValueConverter returning object, paid identically in both versions.

Test plan

• Open a subtitle file and verify start/end/duration times display unchanged in the grid
• Toggle frame mode (hh:mm:ss.ff) and verify times render correctly
• Set a video offset (CurrentVideoOffsetInMs ≠ 0) and verify displayed times include the offset in both time and frame mode
• Verify empty/unset time cells show 00:00:00,000 (time mode) / 00:00:00.00 (frame mode)
• Edit a time cell and verify the typed value round-trips correctly in both time and frame mode, and that invalid input falls back to 00:00:00,000

🤖 Generated with Claude Code

[ivandrofly]

[Copilot]

Pull request overview

Optimizes TimeSpanToDisplayFullConverter to reduce steady-state allocations/GC pressure during UI grid rendering by reusing formatting state and switching parsing to span-based tokenization.

Changes:

• Reuse a single TimeCode instance during Convert to avoid per-call TimeCode allocations.
• Cache zero-time fallback strings for frame/time mode.
• Refactor ConvertBack parsing to use Span.SplitAny and unify frame/time parsing paths.