Finding similar videos, and setting up FFmpeg

The Videos tab needs FFmpeg installed on your machine. Trawler does not ship it. Until FFmpeg is there, the tab shows FFmpeg required and the match button will not run.

Setting up FFmpeg

When FFmpeg is missing, the Videos tab says:

"Video matching needs FFmpeg. Install ffmpeg and ffprobe, then add them to your PATH — or set the ffmpeg location in Settings → Scan performance."

The settings page it means is Settings → Scanning & performance. There is also a Download FFmpeg link on that empty state, and an Open FFmpeg settings button that takes you straight there.

Trawler needs two programs, not one: ffmpeg.exe and ffprobe.exe. They ship together in every normal FFmpeg download, so if you have one you almost certainly have the other — but if only one is reachable, matching stays blocked.

Two ways to point Trawler at it

Approach What to do
On your PATH Unzip FFmpeg somewhere permanent and add its bin folder to your Windows PATH. Leave the FFmpeg setting in Trawler empty.
A specific copy Settings → Scanning & performance → FFmpeg location → Change… and pick ffmpeg.exe.

If you pick a specific ffmpeg.exe, ffprobe.exe must sit in the same folder. Trawler looks for it beside the file you chose and does not fall back to your PATH — that is deliberate, because pointing at one build and silently using another build's ffprobe is worse than a clear failure.

Clear puts you back to "use whatever is on the PATH".

Checking it worked

Settings → Scanning & performance → FFmpeg location shows a status line under the path:

Line Meaning
✓ FFmpeg found — … Working. The rest of the line is the version FFmpeg reported.
✓ FFmpeg found Working, but it did not report a version.
✗ ffmpeg not found / ✗ ffprobe not found / ✗ ffmpeg, ffprobe not found Names exactly which of the two is missing.
✗ FFmpeg not found Neither could be checked.

Trawler re-checks each time you open the Videos tab and each time you come back to the results view, so you do not have to restart it after changing the setting.

If you added FFmpeg to your PATH rather than setting a path in Trawler, restart Trawler before retrying — a running program does not see PATH edits made after it started.

What gets matched

Videos are compared by how they look, frame by frame, so a re-encode, a resize or a different container still matches the original. They are not exact copies — see Reviewing similar results.

By default these file types are considered: .mp4, .mkv, .avi, .mov, .wmv, .webm, .m4v, .mpg, .mpeg, .flv.

Two things a video needs to be considered at all:

  • It has to be in your scan results. Matching reads the files the scan already found, so if your filter excluded video types, or the folder was never scanned, nothing shows up here.
  • It has to run 10 seconds or longer. Shorter clips are skipped quietly — they are not reported as errors.
  • It has to have something in the picture. A clip that is blank all the way through — an all-black recording, a capture that never started — gives Trawler nothing to compare, so it is left out. These are counted on the status line while the match runs ("2 nearly blank videos left out of the match") rather than reported as errors, because there is nothing wrong with the file.

A video that takes longer than 60 seconds to read is abandoned and skipped, as is one FFmpeg cannot open. Both are recorded in Scan report → Scan errors under the type Video.

Running a match

Open Similar files, choose the Videos tab, and use Find similar videos.

Video matching is the slowest thing Trawler does — the empty state says so: "Scan videos to find near-duplicates. This can take a while." You can cancel; the work already finished is kept, so starting again does not redo it.

Above the results, Matching carries one control: a Similarity slider running from 50% to 100%, set to 90% by default. Lower it to catch heavier re-encodes; raise it if you are getting matches you disagree with. Hover the slider to read the current setting; while you drag, the figure follows the handle.

Moving the slider usually re-groups the existing results straight away. When a change needs the videos read again, a bar appears reading "Settings changed since the last video match." with Re-run and Revert.

Reading the results

Groups are listed on the left with a header line of the form "N files · size · ~size reclaimable", and you can order them by Reclaim, Best match first, or Count.

Each video in a group has Play for an inline preview, Open for full screen, and Keep / Discard. Compare sits on the group header, in the same place as it does on Images and Documents.

If a preview will not play, you will see "Can't play this video. The format may be unsupported or the file is unavailable." That is Windows failing to play it, not a matching failure — the match itself used FFmpeg, which handles more formats than the built-in player does.

On the free version only the first 10 groups are shown, with a note saying how many more there are.

The side-by-side compare view

On a group header, choose Compare. The compare surface fills the panel: two video panes, headed Compare · Side-by-side. Pressing C on a card opens it on that clip instead.

The left pane is A and the right is B. A is the one you would probably keep; B is the one being compared against it. Back returns to the list, and so does Esc.

A filmstrip along the bottom holds the rest of the group. Click any clip to bring it into B.

The controls

Control What it does
Keep A / Discard A Decide the left file. With Auto-advance after a decision on, Keep A brings on the next clip for comparison and Discard A hands the left side to the clip you were comparing it against. Either way, once there is nothing left to compare against you move on to the next group.
Keep B / Discard B Decide the right file, then move to the next one if Auto-advance after a decision is on.
Previous / Next Step through the other files in the group without deciding anything.
Previous group / Next group Move to another group without going back to the list.
Switch A and B Puts the right-hand file on the left.
Open A full screen / Open B full screen Fills the window with that pane. Leaving it puts you back where you were, at the same position. Whether it carries on playing depends: it does if that was the pane you had selected, or if Play both at once is on — otherwise it comes back paused.
Keep A and discard the rest / Discard all / Clear all The same three batch actions the group list has.
Show comparison details The ⓘ toggle shows or hides the difference table.
More controls Appears only when the window is too narrow for the whole bar. The controls that no longer fit move into it, from the middle of the bar outwards — Keep and Discard never leave.

Auto-advance moves you along; it never decides anything. Advancing is navigation, not a verdict.

Playing the two clips

The transport strip under the panes drives whichever pane is active:

Control What it does
Play or pause K.
Back 5 seconds / Forward 5 seconds J and L, marked -5s and +5s.
Position Drag to scrub.
Move playback to the other video N. Hands playback to the other pane at the same position, playing or paused as it was. If that video can't be played you will see "That video can't be played." and nothing moves.
Play both at once Y. Plays both panes together with the second one muted, so you can watch them side by side.

The on-screen shortcut list (F1) currently labels Y and N with another screen's wording. Both keys do what this table says while the compare view is open.

The comparison details

The ⓘ toggle shows a table beside the panes, in this order: Duration, Resolution, Frame rate, Bit rate, Video format, Pixel format, Color, Audio, File size, Container, Date created and Date modified. Values that differ between the two are shown in bold.

Color reads HDR10 or SDR. Audio reads Mono, Stereo or a channel count. Anything FFmpeg did not report shows a dash.

If a pane will not play, it reads "Can't play this video. The format may be unsupported or the file is unavailable." The details table still works — those figures came from the match, not from the player.

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