为视频添加封面
为视频设置封面 —— 用你自己的图片，或视频里的某一帧。
Nothing is uploaded — this runs on your own device. Which is why the speed is your computer’s: a faster processor and more memory finish sooner, and a large file on a modest machine can take a few minutes. Please leave this tab open while it works.
一切都在你的浏览器中运行——没有上传任何内容。
如何使用 为视频添加封面
- 把视频拖进来。
- 选择一张图片，或指定要截取哪一刻的画面。
- 点击「处理视频」并下载带新封面的文件。
关于 为视频添加封面
Add Thumbnail to Video writes a cover image into the file itself, so Windows Explorer, macOS Finder, VLC and most media players show that picture instead of the first frame — which on a lot of videos is a black square or a title card mid-fade.
The cover is stored as a second video stream marked attached_pic, which is how MP4 carries artwork. Everything else is copied across untouched: the picture and the sound are not re-encoded, so there is no quality loss and even a long file finishes in seconds rather than minutes. If you would rather not supply an image, the tool can pull a frame from any moment you name and use that.
Two honest limits. This sets the cover inside the file — it is not the same as a YouTube or Vimeo thumbnail, which those sites store on their own servers and which you set when you upload. And cover art is an MP4 and M4V feature; the output is always MP4 for that reason, so a WebM or MKV source comes back as MP4. Everything runs in your browser and no file is uploaded. To pull stills out instead of putting one in, use video to GIF, and compress video if the file needs to be smaller.
常见问题
Will this change my YouTube thumbnail?
No. YouTube, Vimeo and similar sites keep the thumbnail on their own servers and you set it when you upload. This writes a cover image into the video file, which is what your computer and desktop players read.
Does it re-encode the video?
No. The picture and the sound are copied straight across and only the cover image is added, so there is no quality loss and the job takes seconds even on a large file.
Can I use a frame from the video instead of my own image?
Yes. Choose "A frame from this video" and give the time in seconds — that frame is captured and used as the cover.
Why is the output always MP4?
Cover art is a feature of the MP4 family. A WebM or MKV source is remuxed to MP4 so the artwork has somewhere to live; the video and audio streams themselves are still copied without re-encoding.
My player still shows the old picture.
Some file managers cache thumbnails. Copy the file to another folder, or clear the thumbnail cache, and the new cover appears.
Is the video uploaded anywhere?
No. The whole thing runs in your browser using WebAssembly — the file never leaves your device.