If you are a researcher, engineer, or QA professional, you know the frustration of loading heavy, resource-intensive software just to compare two video clips. Whether you are evaluating a new compression algorithm, auditing rendering output, or benchmarking an AI video upscaling model, you need a workflow that is fast, accurate, and lightweight.

TwinLens is a browser-based comparison tool that runs entirely locally — no uploads, no servers, no sign-in. Drop in 2, 3, or up to 4 videos and you are ready to analyze within seconds.

What we compare in this tutorial: Output clips from the SeedVR2 video restoration model — a realistic case where frame-level differences matter and a fast iterative loop is essential.

Getting started: drop your videos

Navigate to the TwinLens comparison page and drop your video files into the panels — up to four at a time. TwinLens automatically synchronizes playback, normalizes display size across all clips, and keeps them aligned with continuous drift correction. The toolbar switches into video mode and every clip begins looping in sync immediately.

For 3 or 4 clips, TwinLens lays them out in a horizontal row, vertical stack, or 2×2 grid — perfect for ablation studies, multi-checkpoint comparisons, or A/B/C/D variant reviews.

TwinLens video comparison UI showing two synchronized video clips side by side with the toolbar in video mode
TwinLens in video mode — two clips loaded and playing in sync. The toolbar exposes all comparison and export controls. Playback is looped automatically; the seek bar and speed control are active.
Toolbar reference (left to right):
i Info · T Labels · ⊞ Side-by-side · ⧉ Slider · 👁 Peek · ↺ Loop · ⏸ Play/Pause · seek bar · 1x Speed · ⏺ Record · ⤢ Fit/Actual size · ⬚ Zoom · 📷 Snapshot · ↺ Reset

Views, metadata, and zoom

TwinLens gives you three comparison views — side-by-side, slider, and peek — plus per-clip metadata (i for codec, resolution, frame rate, duration), editable labels (T) that carry into exports, and a size toggle between fit-to-viewport and actual 1:1 pixels for evaluating sharpness at native resolution.

Exporting your comparison

Once you have tuned your view, TwinLens gives you two export paths:

  1. Snapshot — pauses playback and saves a PNG of the current comparison frame, including any active labels and view mode. Use this to capture a specific artifact or frame of interest.
  2. Record — starts and stops a screen recording of the active comparison view, saved as a video file. You can adjust playback speed before recording, so a slow or fast source clip can be captured at a viewer-friendly rate. The output is ready to drop directly into a slide deck, Notion doc, or bug report.
TwinLens snapshot of a paused video comparison — side-by-side view showing open eyes in both the reference and SeedVR2 output
Pause at the exact frame you need and snapshot it — here we captured the moment the subject's eyes are open to compare detail quality between the reference and SeedVR2 output.
Pro tip for very short clips: TwinLens loops playback continuously. Set a comfortable speed, hit record, and let it run for a few seconds — you get a smooth, watchable loop instead of a two-frame blink.
Slider view at increased speed — recorded for a few loops and exported directly from TwinLens.
Side-by-side view at 1× speed — both clips loop in sync, making it easy to spot temporal differences across multiple passes.
Try it yourself: Open this live demo to compare a low-quality and high-quality video side by side in slider view — drag the slider to reveal differences in real time.

Typical workflow for ML video evaluation

A common pattern when comparing model outputs:

  1. Drop the reference clip (ground truth or baseline) on the left and the model output on the right.
  2. Use actual size mode and switch to slider view to scan for sharpness differences and temporal artifacts frame by frame.
  3. Add labels via the T icon — e.g. baseline vs SeedVR2 4×.
  4. Snapshot key frames that illustrate regressions or improvements.
  5. Record a short looped segment at 0.5× speed for your model card or PR review.

TwinLens is built to make technical image and video comparison faster and more intuitive — entirely in the browser, with no data leaving your machine. If it improves your workflow, consider recommending it to your team.

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