Shorts Video/Audio Combiner

Shorts Video/Audio Combiner — User Manual

A single self-contained HTML file that trims a video and an audio track to

a short-form length and combines them, entirely inside your web browser

using ffmpeg (compiled to WebAssembly). Nothing is uploaded anywhere — all

processing happens on your own machine, in the browser tab.

## 1. Requirements

- A modern desktop browser (Chrome, Safari, or Firefox)

- An internet connection the first time you use it (it downloads the

ffmpeg engine, ~30MB, from a CDN)

- Nothing else — no installation, no Python, no server, no ffmpeg binary

## 2. Opening it

Unzip the folder and double-click **index.html**. It opens directly in

your default browser — that's it, there's no server to start and no

command line involved.

## 3. Using the app

1. **Video file** — click **Choose File** and pick the source video.

2. **Audio file** — click **Choose File** and pick the audio track to lay

over it.

3. **Audio volume (0.0 – 2.0)** — multiplier applied to the audio track's

volume. `1.0` keeps the original level; `0.08` makes it very quiet.

4. **Max short duration (seconds)** — the output is capped to this length

when short-form mode is on. `178` matches the common ~3-minute limit

used by YouTube Shorts / TikTok-style short-form video.

5. **Short-form mode** checkbox:

- **Checked**: output is cropped/padded to a 1080×1920 portrait frame

and capped to the max duration above.

- **Unchecked**: the original video's dimensions and full length are

kept.

6. Click **Convert**.

- The first run downloads the ffmpeg engine (~30MB) — you'll see

"Loading ffmpeg core..." in the status line.

- **While it's actually processing, the page will look frozen** (the

status line stops updating and the tab won't respond to clicks) —

this is expected, not a crash. Everything runs on the same thread as

the page itself, so there's nothing left to keep the UI moving while

ffmpeg works. Just wait for it; don't close the tab or click Convert

again.

- This can take anywhere from several seconds to a couple of minutes

depending on your machine and the video's length, since it's software

encoding running in the browser rather than your GPU/native ffmpeg.

7. When it finishes, the status line says "Done." and a preview with a

**Download** link appears below the log.

## 4. Troubleshooting

- **"Please choose both a video file and an audio file."** — one or both

file pickers were left empty.

- **The page hangs on "Loading ffmpeg core..." and never gets past it** —

check your internet connection; the engine is fetched from a CDN on

first use, and a firewall or ad-blocker that blocks `cdn.jsdelivr.net`

will prevent this.

- **The tab looks frozen after clicking Convert** — see the note in step 6

above; this is expected while ffmpeg is running, not an error.

- **The tab crashes or the browser warns the page is unresponsive** — this

can happen with a very long or very high-resolution source video, since

everything is decoded/encoded in-browser with no hard limit on memory

use. Try a shorter or lower-resolution source.

- Any other error is shown in the red box above the log, with ffmpeg's own

output underneath it for more detail.