Free online PART to MP4 converter

A video interrupted during a browser or download-manager transfer may be left as .part and rejected by a phone, editor, or media player. The download must normally finish before the file can be remuxed or transcoded into MP4 for playback, sharing, or archiving.

What the PART format is

.part is a temporary filename extension, not a video container or codec. Firefox commonly uses names such as video.mp4.part; some download managers use the same convention, while Chromium-based browsers commonly use .crdownload.

The partial data may ultimately be an MP4, WebM, or another file type. Firefox, download managers, and peer-to-peer applications may also keep resume or recovery information separately, so only the program that started the transfer may be able to complete it. The extension alone does not identify the data inside.

What the MP4 format is

MP4 is a media container supported by phones, browsers, televisions, editing applications, and many sharing platforms. It can hold video and audio encoded with different codecs; H.264 video with AAC audio is a common combination for broad compatibility. H.265/HEVC can reduce file size at similar visual quality but is less universally supported.

MP4 can be created by remuxing compatible streams into a new container or by transcoding them into compatible codecs. Remuxing is fast and preserves the source quality. Transcoding is slower and can reduce quality, but it handles sources whose codecs or container cannot be used directly in MP4.

How to convert a completed download

1. Finish or restore the download. Open the original browser or download manager, choose its resume, retry, verify, or finalize option, and wait until the transfer reaches 100%. Do not rename, move, or edit an active temporary file. A successful download normally removes .part and restores the intended filename.

2. Check the completed file. If the file still ends in .part, confirm its intended type from the download page, original filename, or application that created it. Renaming video.part to video.mp4 changes only the filename; it does not convert the contents or restore missing data. Make a copy before testing a manually renamed file.

3. Inspect the streams when the type is uncertain. FFmpeg's ffprobe or the MediaInfo desktop application can identify the container and audio/video streams:

   ffprobe "video.part"

   A valid, complete video can usually be opened in VLC, HandBrake, or another media player even if its extension is wrong. Errors such as moov atom not found, unexpected end-of-file, or invalid input usually indicate an incomplete download, a non-video file, or a proprietary format.

4. Remux compatible streams with FFmpeg. For a completed source with video and audio streams that MP4 supports, run:

   ffmpeg -i "video.part" -map 0:v:0 -map 0:a? -c copy "video.mp4"

   This copies the streams without re-encoding. If the source is already a complete MP4 and only its extension is wrong, renaming it after verifying the contents may be sufficient. Remuxing can fail when the source contains unsupported codecs, incompatible subtitles, or damaged metadata.

5. Transcode incompatible media. H.264/AAC is a practical compatibility target:

   ffmpeg -i "video.part" -map 0:v:0 -map 0:a? -c:v libx264 -preset medium -crf 23 -c:a aac -b:a 192k -movflags +faststart "video.mp4"

   Lower -crf values generally produce higher quality and larger files. Transcoding takes longer and introduces generation loss, so use it when remuxing is unsuitable or the target devices require H.264/AAC.

6. Use a graphical application. In HandBrake, open the completed file, choose a suitable preset such as Fast 1080p30, select MP4 as the format, and choose Start Encode. In VLC, use Media → Convert/Save → Add → Convert, choose an MP4/H.264 profile, specify an output filename ending in .mp4, and start the conversion. These applications can convert valid media but cannot reconstruct an unfinished download.

7. Use 101convert.com without installing software. Upload only a completed file containing a recognizable video stream. An active or truncated .part file may be rejected or produce an incomplete result; do not upload confidential media unless the service's handling and retention terms are acceptable.

Quality and compatibility limits

A partial MP4 may contain most of the media but still be unplayable because its index and metadata, including the moov atom, are commonly written near the end. The -movflags +faststart option places output metadata near the beginning for faster web playback, but it cannot repair a truncated input.

Remuxing preserves source quality because it copies the encoded streams. Transcoding changes the codecs and may reduce quality, although H.264/AAC usually improves playback compatibility. Encrypted, DRM-protected, segmented, or application-specific downloads may require the original browser, download manager, or service to finalize them; generic converters and renaming cannot bypass those requirements.