Free online PART to WEBM converter

A .part file usually indicates an unfinished Internet download, while WEBM is a completed video format used by browsers and web applications. You must finish or recover the download before converting it; changing the filename extension cannot repair missing video data.

What the PART format is

.part is a temporary download extension rather than a standard media container. Firefox and some download managers create files such as video.mp4.part while receiving data, then remove the suffix after the download completes. An interrupted download leaves a partial file that may contain an incomplete MP4, WebM, or another format.

Resume the download in the program that created it whenever possible. If the original download is no longer available, check the file with ffprobe filename.part or a system file-identification tool; the extension alone does not identify its contents.

What the WEBM format is

WEBM is an audiovisual container designed for web playback. It commonly stores VP8, VP9, or AV1 video with Opus or Vorbis audio and is supported by current browsers, HTML5 video players, and many streaming workflows.

WEBM is useful when browser compatibility, open codecs, and relatively small web video files matter. It is not a universal replacement for MP4: older devices, editing applications, and some smart TVs provide better support for H.264/AAC MP4.

How to actually convert PART to WEBM

1. Resume the download first. Do not convert the temporary file while the browser or download manager is still writing it.
2. Make a backup copy, then identify the completed source container with ffprobe input.part. If FFmpeg reports truncated input or cannot detect a stream, the download is incomplete or damaged.
3. If the file is complete but has only a temporary suffix, rename the copy to the detected source extension, such as input.mp4. Renaming changes the label only; it does not perform conversion.
4. Install FFmpeg and encode the video to broadly compatible WEBM with:

ffmpeg -i input.mp4 -c:v libvpx-vp9 -crf 31 -b:v 0 -c:a libopus -b:a 128k output.webm

Use a lower VP9 -crf value for higher quality and a larger file; values around 30–35 are common starting points. If the source already contains WebM-compatible VP8, VP9, AV1, Opus, or Vorbis streams, try remuxing without re-encoding:

ffmpeg -i input.webm -c copy output.webm

You can also convert a completed, recognized video file free on 101convert.com without installing software. An unfinished .part file may be rejected or produce a broken result because the missing portion cannot be recreated.

Quality and compatibility limitations

Re-encoding reduces quality and takes longer than remuxing. A partial download may play only its beginning, lack an index, or fail completely; FFmpeg cannot recover data that was never downloaded. Keep the original completed file because converting to WEBM may remove compatibility with software that expects MP4 or another container.