Free online PART to MKV converter

A .part file usually means a video download has not finished, so media players and editors may reject it. After the download completes, you can package the recovered video in an MKV container for playback, archiving, subtitles, or broader track support.

What the PART format is

.part is generally a temporary filename extension, not a video format or container. Web browsers, download managers, peer-to-peer clients, and programs such as Firefox and eMule use it while saving an incomplete download; related metadata files may record the download state or source information.

The file contains whatever bytes the program has received so far. It may contain the beginning of an MP4, WebM, AVI, or another file, but the extension alone does not identify the underlying format. A partial file normally cannot be converted successfully because indexes, headers, or later media segments are missing.

What the MKV format is

MKV, or Matroska Video, is a multimedia container that can hold video, multiple audio tracks, subtitles, chapters, attachments, and metadata. It supports common codecs such as H.264, H.265, VP9, AV1, AAC, Opus, and FLAC.

MKV is useful when you need to preserve several language tracks or subtitle files in one file. It is a container, not a codec, so converting to MKV does not automatically improve quality or reduce size.

How to convert PART to MKV

1. Finish the download first

Return to the browser or download program that created the file and let it reach 100%. Do not convert, move, or rename the file while the download is active. When complete, the program usually removes .part and restores the original filename.

If the download program stopped permanently, use its resume or recheck function. A missing final segment cannot be reconstructed by a converter.

2. Identify the completed source file

If the extension remains .part after the download is complete, check the original download page, torrent metadata, or the filename before .part to determine whether it is an MP4, WebM, or another supported media file. Rename it only when the underlying format is known, for example movie.part to movie.mp4.

FFmpeg can probe many completed files without changing the name:

ffprobe -hide_banner "movie.part"

A valid result should show at least one video or audio stream and a recognizable container. An error such as “moov atom not found” usually indicates an incomplete or damaged MP4 rather than a conversion problem.

3. Remux the media into MKV

For a completed, compatible source, FFmpeg can change the container without re-encoding:

ffmpeg -i "movie.mp4" -map 0 -c copy "movie.mkv"

-map 0 retains all detected streams, and -c copy avoids generation loss and is usually fast. Replace movie.mp4 with the actual completed source filename.

MKVToolNix provides a graphical alternative. Open MKVToolNix GUI, add the completed video under Multiplexer → Add source files, select the destination filename ending in .mkv, and choose Start multiplexing. Disable unwanted tracks in the track list before starting if the source contains extra audio or subtitle streams.

4. Re-encode only when necessary

If the source codecs are unsuitable for the target player, convert the streams instead of copying them:

ffmpeg -i "movie.mp4" -map 0:v:0 -map 0:a? -c:v libx264 -crf 20 -preset medium -c:a aac -b:a 192k "movie.mkv"

This creates H.264 video and AAC audio, but takes longer and can reduce quality. Lower CRF values increase video quality and file size; the exact compatibility requirement should determine the codec settings.

For a completed and readable media file, you can also use the free converter on 101convert.com without installing software. An online converter cannot repair a genuinely incomplete .part download, and uploading may be unsuitable for private or copyrighted material.

Quality, compatibility, and limitations

• Remuxing with -c copy does not change the encoded audio or video, so quality and size remain nearly the same apart from container overhead.
• Some older televisions, phones, and browsers support MP4 more consistently than MKV. Check the playback device before choosing the container.
• A completed download may still be corrupted or protected by DRM. Conversion tools cannot restore missing bytes or bypass DRM.
• MKV can preserve subtitles, chapters, and multiple audio tracks, but incompatible codecs inside the MKV may still prevent playback on a particular device.