Prompt file imported from kevinnz/SSTV-MEL (.github/prompts/add-sstv-mode.prompt.md). Copyright stays with the author.

Add a New SSTV Mode

I want to add a new SSTV mode to SSTV-MEL. Guide me through the implementation step by step.

Steps

1. Create the mode file in Sources/SSTVCore/Modes/ following the pattern in PD120Mode.swift and PD180Mode.swift
2. Define all timing constants — use explicit named constants matching the published SSTV specification. Include inline comments referencing the spec.
3. Implement the SSTVMode protocol — define image dimensions, line timing, frequency ranges, color encoding order, and VIS code
4. Register the mode in SSTVModeSelection / ModeParameters.swift with its VIS code
5. Add the mode to the CLI — update the SSTVMode enum in DecodeCommand.swift so it's available via --mode
6. Create tests:
   • Unit test for mode timing constants
   • If a sample WAV is available, add a golden-file decode test using PSNR/SSIM comparison
7. Update documentation — add the mode to README.md supported modes list

Key Rules

• Modes are stateless — they define timing and structure, not DSP
• All math uses normalized Double values (0.0–1.0)
• Use time-based decoding with fractional sample interpolation
• Do NOT hardcode sample counts
• Do NOT copy-paste from other modes — share common logic via ModeTimings