Support ffmpeg video export profiles (e.g., `--profile sos`) and passthrough options (e.g., `--pix-fmt`, `--colorspace`)

[Hackshaven]

🧩 Problem / Workflow Gap

Zyra's current video export pipeline does not allow users to:

• Control chroma subsampling, pixel format, or color space
• Avoid Vimeo-related color shifts due to default ffmpeg → Vimeo transcoding behavior
• Specify consistent, reproducible quality profiles (e.g., archival, web, streaming)

This limits visual fidelity and introduces downstream surprises—particularly for workflows requiring color-accurate, high-bitrate, or broadcast-compliant outputs.

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✅ Proposal

We propose two complementary solutions:

1. --profile <name> (High-Level Presets)

Add support for friendly, pre-defined ffmpeg export bundles such as:

--profile sos        # Stream-optimized settings
--profile archive    # ProRes 422, yuv422p, high bitrate
--profile broadcast  # yuv422p10le, BT.709, VBR
--profile lossless   # FFV1, yuv444p, no chroma loss

Each profile would configure a consistent set of ffmpeg flags (codec, pixel format, color space, container, etc.).

2. Low-Level Overrides (Passthrough Controls)

Expose advanced ffmpeg flags for granular control:

--pix-fmt yuv422p
--colorspace bt709
--color_range pc
--codec libx264
--bitrate 20M
--ffmpeg-flags "-g 30 -movflags +faststart"

These can override defaults or augment profiles, enabling full reproducibility and precision.

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🧪 Tests

• Validate output format and pixel structure using ffprobe
• Confirm Vimeo or third-party delivery matches expectations
• Provide example image sequences + round-trip encoding checks

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📚 Documentation

Add a section to the CLI docs describing:

• Available profiles and when to use them
• Tradeoffs (quality vs. size vs. compatibility)
• How to inspect output video with ffmpeg tools

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🔗 Related

• Upstream Vimeo support for passthrough uploads (Pro+ only)
• User-reported color fidelity issues traced to ffmpeg → yuv420p → Vimeo transcoding