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Video Downsample Workflow (GUI)

This tutorial walks through Annolid's built-in Downsample / Rescale Video dialog for single videos and batch folders.

Use this workflow when you want to:

  • reduce resolution and optional FPS for faster downstream processing,
  • apply denoise and contrast adjustments,
  • set one shared default for a folder,
  • override only the few videos that need different settings,
  • set a custom crop for a specific video when reviewing a folder,
  • keep reproducible processing records (metadata.csv and per-video .md files).

Open the Tool

In the desktop app, open:

  • File -> Downsample Video(s)…

The dialog has four tabs:

  1. Input / Output
  2. Processing
  3. Summary
  4. Run

Annolid downsample dialog - Processing tab

This is the main dialog layout. The folder-review flow lives in the Processing tab and opens the sequential per-video override dialog from there.

Step 1: Choose Input and Output

In Input / Output:

  1. Click Select Video for one-file processing, or Select Folder for batch processing.
  2. (Recommended) click Select Folder under Output Folder and choose a clean destination.

If output is left blank, Annolid automatically creates a sibling folder with _downsampled appended to the source folder name.

Step 2: Configure Shared Defaults

In Processing, set the baseline configuration for all videos:

  • Scale Factor: 0.5 halves width/height, 0.25 quarters them.
  • Use specified FPS for all videos: checked = force one FPS for all files; unchecked = keep source FPS per video.
  • Apply Denoise: useful for noisy recordings.
  • Auto Contrast Enhancement: enables brightness/contrast correction.
  • Auto Contrast Strength: tune from 0.0 to 2.0 (default 1.0).

Crop Options

Use Crop Region as the default crop for the batch. If one video needs a different crop, you can override it later during folder review.

  • Turn on Enable Crop Region.
  • Set x, y, width, height manually, or
  • Click Preview & Crop First Frame to draw crop visually.

Step 3: (Folder Only) Review Videos One by One

If your input is a folder, you can apply per-video exceptions, including a different crop for a specific video.

Annolid downsample dialog - per-video review

  1. Click Review Videos One by One (Folder Input).
  2. For each file:
  3. keep defaults with Skip,
  4. or set custom values, including a one-off crop, and click Save & Next.
  5. Use Previous to revisit earlier files.
  6. Use Load Folder Defaults to reset the current video back to shared settings.
  7. Click Finish when done.

Best practice: only save overrides for true exceptions. Keep the common case in shared defaults. If one recording was captured from a different camera angle, use the review dialog to give that video its own crop without changing the rest of the folder.

Step 4: Verify the Summary

Open Summary and confirm:

  • input source and mode,
  • output folder,
  • default processing values,
  • number of per-video overrides,
  • run actions selected.

Use Refresh Summary after making changes.

Step 5: Run Processing

Open Run and select at least one action:

  • Rescale Video: re-encodes videos with current settings.
  • Collect Metadata Only: writes metadata/report files without re-encoding.

Click Run Processing to start.

Output Artifacts

Annolid writes audit-friendly outputs in the target folder:

  • metadata.csv with video metadata,
  • one *.md report per processed/inspected video,
  • processed *_fix.mp4 videos when Rescale Video is enabled.

Per-video markdown reports include:

  • effective downsample parameters,
  • whether per-video review override was used,
  • whether the override included a custom crop,
  • FFmpeg command used (when re-encoding),
  • resulting metadata.

Practical Presets

Preset A: Fast review copies

  • Scale factor: 0.5
  • Override FPS: on, FPS: 15
  • Denoise: off
  • Auto contrast: off
  • Crop: off

Use when you want lightweight videos for annotation speed.

Preset B: Low-light behavior recordings

  • Scale factor: 0.5
  • Override FPS: off
  • Denoise: on
  • Auto contrast: on
  • Strength: 1.1 to 1.3

Use for noisy, dim recordings where object visibility is poor.

Preset C: Arena-only crop batch

  • Scale factor: 0.5
  • Override FPS: off
  • Denoise: optional
  • Auto contrast: optional
  • Crop: on (shared arena rectangle)
  • Per-video review: only for camera-shift outliers

Use when most videos share a stable camera angle.

Preset D: One outlier video with a different crop

  • Scale factor: 0.5
  • Override FPS: off
  • Denoise: optional
  • Auto contrast: optional
  • Shared crop: on for the main arena
  • Per-video review: use a custom crop for the outlier video only

Use when a folder mostly shares one arena view, but a single file needs a tighter or shifted crop.

Troubleshooting

  • "Run" does nothing: ensure at least one action is checked (Rescale Video or Collect Metadata Only).
  • Per-video review is disabled: it is available only for folder input mode.
  • Custom crop not sticking for one file: open the per-video review dialog, set the crop for that video, and click Save & Next or Finish before running the batch.
  • Crop not applied: confirm Enable Crop Region is checked and all crop values are valid integers with positive width/height.
  • FPS errors: if override is enabled, FPS must be numeric and > 0.
  • Unexpected output location: check Summary to confirm the resolved output folder before running.