How to generate a thumbnail overview grid for a video
- Step 1Load the archive clip — Drop an MP4, MOV, MKV, WebM, or AVI onto the tool. It reads locally into FFmpeg.wasm; nothing is uploaded. One clip per run.
- Step 2Pick grid density by clip length — For a quick catalogue thumbnail, 4x4 (16 frames) is enough. For long archive masters where you want fine coverage, go up to 10x10 (100 frames). Columns and Rows each accept 1-10.
- Step 3Set Tile width for the use — Small (120-240px) for a lightweight catalogue thumbnail; larger (640-1280px) when archivists need to read detail for QC or rights review. Height auto-scales to the source aspect.
- Step 4Generate the overview — Run it. The tool probes duration, samples one frame per equal time slice across the whole clip, and tiles them into one PNG. Larger masters take longer because FFmpeg.wasm decodes the sampled frames in the browser.
- Step 5File the PNG with the asset — Download
<yourfile>-grid.pngand store it alongside the original or attach it to the MAM/DAM record as the clip's visual reference. - Step 6Need a machine-readable index too? — The grid is an image for humans. If you also want cut points as data for automated indexing, run scene-detector, which outputs a JSON list of cut timestamps.
Overview-grid density by clip length
Rough guidance for archive cataloguing. Total frames = columns x rows.
| Clip length | Suggested grid | Frames | Approx interval |
|---|---|---|---|
| Under 2 min | 3x3 | 9 | every ~12s on a 2-min clip |
| 2-15 min | 4x4 | 16 | every ~50s on a 15-min clip |
| 15-60 min | 6x6 | 36 | every ~97s on a 60-min clip |
| Over 60 min (master) | 10x10 | 100 | every ~36s on a 60-min clip |
Tile width by archive purpose
Pick tile width to balance catalogue weight against inspection detail.
| Tile width | Use | Trade-off |
|---|---|---|
| 120-240px | Lightweight catalogue thumbnail | Small file; fine for ID, too small for QC |
| 320px (default) | General overview record | Balanced size and readability |
| 640-1280px | QC / rights / forensic inspection | Large file; reads fine detail per frame |
Tier limits for video tools
Archive masters are large — check the file-size ceiling for your plan. No duration cap.
| Tier | Max file size | Files per batch |
|---|---|---|
| Free | 1 GB | 1 |
| Pro | 10 GB | 5 |
| Pro + Media | 100 GB | 50 |
| Developer | 100 GB | Unlimited |
Cookbook
Cataloguing recipes archivists actually use, with the exact options.
Quick catalogue thumbnail for a short clip
A compact 3x3 at 200px is enough to identify a sub-2-minute clip and tag it in the MAM.
Options: Columns=3 Rows=3 Tile width=200 Frames=9 Output: a small overview-grid.png to attach to the record
Standard 4x4 overview for a mid-length master
A 12-minute interview master gets a default 4x4 at 320px — readable enough to confirm content and speakers.
Options: Columns=4 Rows=4 Tile width=320 Duration=720s -> 16 frames, ~42s apart Output: master-grid.png
Dense 10x10 index of a long master
For a 90-minute master where you want fine coverage, a 10x10 (100 frames) maps the whole runtime in one image.
Options: Columns=10 Rows=10 Tile width=240 Frames=100, ~53s apart on a 90-min master PNG width ~ 10 x 240 = ~2400px Output: a dense visual index
QC inspection sheet at high tile width
When checking for damage, dropouts, or watermarks, raise tile width so each frame is inspectable. Keep the grid moderate to manage file size.
Options: Columns=5 Rows=5 Tile width=1280 Frames=25 PNG width ~ 5 x 1280 = ~6400px Output: a very large, detailed QC sheet
Pair the grid with a data index
Store the overview PNG for humans and a JSON cut list for automation. Run both tools on the same file.
1. frame-grid-maker -> master-grid.png (visual record)
2. scene-detector -> master-scenes.json (cut data)
/video-tools/scene-detector
Attach both to the MAM record.Edge cases and what actually happens
No labels or timecode on the grid
Not supportedThe overview is a plain mosaic — no filename, timecode, or cell numbers are burned in. Track that metadata in your MAM/DAM record; the PNG is purely the visual index.
One file at a time, not a batch cataloguer
Single file onlyThis tool does not accept multiple files at once, so it is not a bulk archive processor on its own. Process clips one by one. The batch counts in the tier table apply to tools built for multiple inputs.
Master file exceeds the tier size limit
RejectedA master above your plan's file-size ceiling (1 GB Free, 10 GB Pro, 100 GB Pro + Media / Developer) will not process. Either upgrade the tier or generate the grid from a smaller proxy of the master.
Duration metadata missing from the container
ErrorSome archive transfers or fragmented captures lack usable duration; the tool then throws "Could not determine video duration." Remux to a clean container and retry.
Dense grid on a very short clip
ExpectedAsking for 100 frames from a 20-second clip samples every ~0.2s, so cells repeat visually. Use a smaller grid for short assets.
Mixed aspect ratios across the archive
PreservedEach tile keeps the source aspect ratio, so a 4:3 archive clip and a 16:9 one each tile faithfully — but the sheet shape differs per asset. That is expected; the grid reflects the source frame shape.
Baked-in black bars in old transfers
PreservedLetterbox/pillarbox bars in the source appear in every tile; the tool does not crop. Crop with video-cropper first if you want clean overview frames.
Very large file on a low-RAM workstation
PerformanceFFmpeg.wasm uses the browser tab's memory. A huge master within your size limit can still be slow or memory-bound on modest hardware. Use a proxy or a stronger machine, and close other tabs.
Columns/rows over 10 or tile width under 120
ClampedGrid dimensions cap at 10 each (max 10x10 = 100 frames) and tile width has a 120px floor. Out-of-range requests are silently adjusted to the nearest allowed value.
Audio-only or stream with no video
ErrorWithout a video stream there are no frames to tile and the run fails. This tool needs a video track; audio assets belong with the audio tools.
Frequently asked questions
Can I catalogue a whole folder at once?
Not in one pass — this tool takes one file per run and outputs one PNG. For a folder, process each clip individually. The batch limits in the tier table apply to tools that accept multiple files.
Does the grid include the filename or timecode?
No. It is a clean mosaic of frames with nothing burned in. Keep filenames and timecodes in your MAM/DAM record; the PNG is the visual reference only.
How representative is the overview of the whole clip?
Very — frames are sampled at equal time intervals across the entire duration, so the grid spans the clip evenly rather than clustering at the start. More cells means finer coverage.
What is the maximum coverage I can get?
10x10 = 100 frames, the largest grid. For more granular indexing than that, generate grids over halves of the master or use thumbnail-extractor for arbitrary frame counts.
Will rights-restricted footage be uploaded?
No. Processing is entirely in-browser via FFmpeg.wasm. The footage never leaves your machine, which is essential for restricted or unreleased archive material.
How large a master can I process?
Free up to 1 GB, Pro 10 GB, Pro + Media and Developer 100 GB. There is no duration cap — only the file-size ceiling per tier. For larger masters, catalogue from a proxy.
What output format is the overview?
A single PNG named <yourfile>-grid.png. PNG keeps the frames artefact-free, which matters when archivists zoom in for QC.
Can I also get the cut points as data?
Yes, with a separate tool: scene-detector outputs a JSON list of detected cut timestamps. Pair it with the visual grid for both human and machine indexing.
What input formats are supported?
MP4, MOV, MKV, WebM, and AVI. The tool probes the container and samples the video stream without re-encoding the whole file.
Why is a long master slow to process?
FFmpeg.wasm decodes the sampled frames in the browser on your CPU, so heavier files take longer. It only decodes the frames it samples, but big files still take more time and memory.
Do mixed aspect ratios cause problems?
No problem — each tile preserves its source aspect, so a 4:3 clip and a 16:9 clip each tile correctly. The sheet shape will differ between assets, which is expected.
Should I crop letterboxing first?
If the source has baked-in black bars and you want clean overview frames, crop with video-cropper before generating the grid. Otherwise the bars appear in every tile.
Privacy first
Every JAD Video tool runs entirely in your browser via WebCodecs and FFmpeg (WebAssembly). Your video files never leave your device — verified by zero outbound network requests during processing.