Three optional pieces around your main video: a still image held at the very start, a clip before it, and a clip at the end or dropped in at a moment you choose. Everything is matched to the main video, so clips of different sizes and shapes can be used without preparing them first. The running order is shown, with what will happen to each piece, before anything is encoded.
The thumbnail is a real part of the video rather than a poster frame stored in the file. Poster support is inconsistent across players, and the platforms people usually mean — YouTube, Instagram — take their thumbnail at upload and ignore whatever the file carries. A couple of seconds of the image at the front works everywhere, which is what is actually wanted even when it is called a thumbnail. Placing the outro at a moment rather than the end splits the main video around it, so the video resumes afterwards.
How mismatched pieces are handled
-
Nothing is refused for being the wrong size:
an intro at 4K and a video at 1080p can be joined. Everything is re-encoded to the main video, and the list says which pieces will be changed and how before you commit to the wait.
-
A different shape is fitted, not stretched:
blurred fill scales the piece to fit and puts a blurred copy of it behind, so nothing is cropped and nothing is black. That matters most for an intro, which is usually a logo — filling and cropping would cut its edges off.
-
Silence is generated where a piece has none:
a still image and a silent intro both need their place in the audio track. Without it the sound ends early and everything after it plays out of step with the picture.
-
Everything is re-encoded, including your main video:
joining means writing one new file, so the main video is decoded and encoded again along with the rest. That costs a little quality, which is unavoidable in any browser.
The thumbnail is real video, not a file's metadata
Held-image thumbnails stored as container metadata are unreliable in practice: platform support is inconsistent, and the two places most people mean — YouTube, Instagram — take their thumbnail at upload and ignore whatever the file itself carries. The [msm_tool slug="video-intro-outro"] holds the chosen image as a couple of seconds of actual video at the very start instead, which plays correctly everywhere because it is not depending on a player to notice it.
An outro at the end, or dropped in at a moment
Left at its default, the outro plays after the main video ends. Given a specific timestamp instead, it splits the main video at that point, plays, and the rest of the main footage resumes afterwards — useful for a mid-roll card without needing a separate cutting step first.
Mismatched pieces are fitted, never stretched
An intro or outro in a different shape from the main video is scaled to fit and the space around it filled with a blurred copy of itself, rather than stretched to force a match. That matters most for an intro, which is usually a logo: cropping to fill would cut its edges away, while filling and stretching would distort it, and neither is what anyone actually wants from a brand mark.
Silence fills whatever has none
A still thumbnail and a silent intro clip both need something written to the audio track for their duration. Without it the audio would finish early relative to the picture, and everything after that point would play out of sync for the rest of the file.
The main video is re-encoded too
Joining pieces together means writing one continuous new file, so the main video is decoded and encoded again along with everything added around it — not just the intro and outro. That costs a small amount of quality, which is unavoidable in a browser regardless of how little the main footage itself needed to change.
Where the sound can go missing
MP4 audio needs the AAC codec, which Firefox cannot encode on any platform and no browser can encode on desktop Linux. The page states this before the run starts. Chrome, Edge and Safari keep the audio.