Video Quality Comparator
A video compressor creates a new file; this comparator inspects corresponding moments in two files you already have. It decodes both video tracks, matches the comparison by elapsed time from the reference, and calculates 8×8 block luminance SSIM plus RGB mean absolute error. Select a row to see the reference, comparison and highlighted difference frames. If the comparison has ended or a decoder provides no frame at that time, the slot is reported missing instead of borrowing a neighbouring score.
Key features
- Align reference and comparison MP4/WebM frames by elapsed playback time
- Calculate 8×8 block luminance SSIM and RGB MAE/MSE from decoded pixels
- Inspect reference, comparison and difference frames in a selectable table
- Show missing frames caused by video duration or time offset separately
- Reject mismatched resolutions by default, with explicit comparison resizing
- Download per-frame timestamps and metrics as CSV or JSON
How to use
- Choose a reference and comparison video, or load one of the three real-video examples.
- Set sample FPS, comparison time offset and resolution policy.
- Run the comparison to decode and score both tracks at corresponding times.
- Select a frame row to inspect both pictures and their highlighted difference.
- Review missing frames and average scores, then download frame-level CSV or JSON.
Use cases
- Find scenes with the most visible loss after encoding a video.
- Detect missing comparison frames when an edited file ends before the original.
- Adjust a slight time offset and review corresponding frames again.
Frequently asked questions
Does SSIM 1 mean the two files have identical bytes?
No. This tool compares luminance structure in decoded, reduced-size frames. Its identical example gives SSIM 1 and RGB error 0, but it does not compare file bytes, audio or metadata.
What score does a missing frame receive?
None. A moment beyond the comparison video's end or without a decoded covering frame is marked missing and excluded from averages. If every slot is missing, the tool reports an alignment error.
What if resolutions differ?
Strict mode rejects them by default. Explicit resize mode stretches the comparison picture to the reference analysis dimensions, even when aspect ratios differ, so resizing loss becomes part of the score.
Is this standard full-resolution SSIM?
No. It averages non-overlapping 8×8 luminance-window SSIM on frames limited to a 320-pixel long edge. RGB MAE/MSE report colour error separately. It is neither the original Gaussian-window or multiscale implementation nor a VMAF score.
Which files and durations work?
It accepts two MP4/WebM files that your browser can decode. Each may be up to 64 MiB and 0.5–8 seconds; at most 64 reference moments are sampled. Codec support varies by browser.
Are videos uploaded or re-encoded?
No. Both tracks are read locally and only the report is created. The original videos are not changed or exported.
Privacy
Both videos are decoded in this browser tab only. Frames and reports are not uploaded or kept in browser storage. Only CSV and JSON report downloads are created.
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