Videos¶

Adding videos¶

Both dropzones list the picked files with a Grayscale checkbox per file (and All grayscale / All RGB for several at once). From the Videos panel this list appears in an Import Videos dialog. Choose before you click Import or Create Project — it can't be changed afterwards.

Supported formats¶

The container only gets the file open; the codec inside it still has to be one the app can decode — see Codecs.

.pkg.slp projects carry their frames inside the file, so they open with no video files needed at all.

Playback¶

Video decoding uses WebCodecs. The file is demuxed by mp4box.js (MP4), MediaBunny (WebM, MKV, MOV, Ogg, MPEG-TS), or web-demuxer (AVI, WMV, MPEG), which gives frame-accurate seeking rather than the approximate seeking you get from an HTML <video> element. Playback speed runs from 0.25× to 8×.

Codecs¶

WebCodecs decodes, at 8-bit:

• H.264, HEVC/H.265
• VP8, VP9
• AV1

MJPEG works too — the app decodes it as per-frame JPEGs.

Everything else needs converting first: MPEG-½, MPEG-4 ASP (Xvid/DivX), MS-MPEG4, WMV 1–3, VC-1, and 10-bit H.264/HEVC, which WebCodecs rejects even though it handles the 8-bit form.

Transcoding (desktop only)¶

When the desktop app opens a video in a codec it cannot decode, it offers to transcode it to H.264 MP4 once and reuse the result thereafter.

The conversion runs disk-to-disk in a native ffmpeg sidecar process — the source bytes never enter the app's memory — so a multi-gigabyte legacy file converts at a flat, small memory cost. The result is cached, keyed on the source file, and written atomically, so an interrupted transcode never leaves a half-file behind.

File ▸ Clear Video Transcode Cache… frees that space when you no longer need it.

ffmpeg -i input.avi -c:v libx264 -pix_fmt yuv420p output.mp4

Checking a video's frames¶

Some videos play fine but don't seek reliably: jumping straight to frame N shows a different image than playing up to it. Common causes are videos from acquisition software, files with B-frames (frames stored out of order), and variable frame rates. The result is labels that look shifted from the animal, or that end up on the wrong image.

When a video opens, the app runs a quick check from what it already knows about the file. If something looks off, the video gets a ⚠ in the Videos panel ("May not show every frame correctly").

For a full check, select the video and click Check Frames… in the Videos panel. It reads every frame in order, then jumps straight to 20 frames and checks each one shows the same image. Long videos can take a few minutes. The result says how many frames read, and lists any that couldn't be read or that showed a different image when jumped to.

If the check finds problems, re-encode the video:

• In the app (desktop, and browsers that can encode the video): pick a quality (High, Medium or Low) and re-encode. The app writes a clean copy next to the original (<name>.reencoded.mp4) and offers to switch the project to it.

• Otherwise the dialog gives an ffmpeg command to run yourself, then use Replace Video. It looks like this:

  ffmpeg -i "input.avi" -c:v libx264 -crf 25 -preset superfast -g 30 -bf 0 \
    -pix_fmt yuv420p -fps_mode passthrough "input.reencoded.mp4"
  

  Part	Why
  -c:v libx264	H.264, which every reader decodes
  -crf 25	Quality: 18 is high, 25 medium, 32 low. Lower is better and bigger
  -preset superfast	Fast to encode
  -g 30	A keyframe every second (30 at 30 fps), so jumping to a frame is quick
  -bf 0	No B-frames, so frames are stored in order and seek exactly
  -pix_fmt yuv420p	8-bit color, which WebCodecs needs
  -fps_mode passthrough	Keeps every frame and its timing as-is

Check and re-encode before you label if you can. Labels are attached to frame numbers, so if the re-encoded copy has a different number of frames and the video already has labels, the app won't switch to it (the labels would land on the wrong images). The project keeps using the original.

When videos move¶

A .slp project stores paths to its videos. Move the videos, or open the project on another machine, and those paths stop resolving.

• File ▸ Replace Videos… ▸ (video name), or Replace Video in the Videos panel, re-points one video at a new file.
• Locate All Missing in the Videos panel (shown only when videos are missing) finds them all at once. In Chrome / Edge you pick one folder and the app matches each missing video by file name anywhere inside it; elsewhere you pick the files.
• The app also looks for the file near the project and next to the old path before asking you.

For remote jobs there is a dedicated path resolution dialog that maps every file the job needs onto a path the worker can see — including auto-detecting the rest of a folder and cascade-filling once it works out the prefix difference. See Remote Compute.

Removing videos¶

The Videos panel lists the project's videos; Remove Video removes the selected one. Removing a video removes its labeled frames with it, so if it has any, the app confirms first.

Exporting a labeled clip¶

File ▸ Export ▸ Labeled Clip (Video)… renders a video with the pose overlay burned in — for talks, for figures, or for showing a collaborator what the data actually looks like. You choose the frame range, which videos to include, and the display settings, with a live preview before rendering.