[Feature] FFmpeg quick sampling: multi-window decoding to detect localized corruption

[Zenrac]

Is your feature request related to a problem? Please describe.

The current FFmpeg quick check only decodes the first N seconds of a media file (for example -t 120 from the beginning)
This could creates blind spots: localized corruption occurring later in the file (or near the end) is never detected
Increasing the decoded duration (or running a full scan) is not viable due to CPU and time constraints

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Describe the solution you'd like

Add a ffmpeg-quick-windows parameter that replaces a single contiguous decode with multiple short decoding windows spread across the media duration

Instead of decoding N seconds from the start, it could:

• Decode a small number of short windows
• Automatically spread them across the file (early / middle / late)
• Keep the total decoded time low

Example behavior and configuration:

• 5 windows × 5 seconds at 0%, 25%, 50%, 70%, 90%

# keep existing seconds parameter
ffmpeg-quick-seconds: 5
# number of decode samples (default: 1 - current behavior)
ffmpeg-quick-windows: 5

Any error or timeout in one of the windows would mark the file as corrupted or suspect

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Describe alternatives you've considered

• Increasing the ffmpeg-quick-seconds value: improves coverage, but with a very poor cost-to-efficiency ratio
• Running a full FFmpeg decode on all files: reliable but not possible for large libraries
• Relying on ffprobe only: fast but does not detect all decoding-time or playback issues

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Additional context

This feature is intended to improve corruption detection in very large media libraries without significantly increasing CPU usage

Implementation concerns / edge cases:

• Libraries with very different media duration will get inconsistent coverage if the number of windows is fixed; scaling the window count automatically based on duration (or providing sensible presets for “short/medium/long” content) would improve consistency
• It may be possible to determine the number of windows automatically based on the media duration, so that enabling a single flag like ffmpeg-quick-sampling: true would be sufficient for most users (with optional advanced overrides maybe?)
• This feature likely requires ffprobe (or equivalent) to retrieve the media duration in order to compute sampling offsets; if duration is unavailable or invalid, the implementation could fall back to the current behavior (single window from the start)
• Short files where multiple windows would overlap or exceed total duration: the sampler should clamp offsets and avoid re-scanning already covered ranges