Free online MKV to MPEG4 converter

A TV, editor, upload service, or media player may reject an MKV file even when it can decode the video inside it. Exporting an .mp4 file with H.264 video and AAC audio is usually required for broad playback and sharing compatibility.

MKV and MPEG-4 formats

MKV is the filename extension for Matroska Video, an open multimedia container. A container can hold video, multiple audio tracks, subtitles, chapters, attachments, and metadata; it does not determine the video or audio codec.

MKV is common for video archives, disc backups, downloaded media, recordings, and files with several language or subtitle tracks. It may contain H.264, H.265/HEVC, AV1, VP9, AAC, Opus, DTS, Dolby audio, PGS subtitles, and other stream types. Device support therefore depends on both the MKV container and its internal streams.

MPEG-4 can refer to several standards. For file conversion, it usually means an MP4 file: the MPEG-4 Part 14 container, normally using the .mp4 extension. It does not necessarily mean MPEG-4 Part 2 video; modern MP4 files commonly use H.264/AVC or H.265/HEVC video.

For the widest compatibility, create an MP4 containing H.264/AVC video and AAC audio. MP4 can carry HEVC, AV1, and other codecs, but older TVs, consoles, and editing applications may not support them. If a recipient specifically requests “MPEG-4,” confirm that it accepts an .mp4 file rather than a different legacy video specification.

Convert the file online

1. Open the MKV-to-MPEG4 converter on 101convert.com.
2. Upload the .mkv file.
3. Select MPEG4 or MP4 as the output format.
4. Start conversion, then download the resulting .mp4 file.
5. Play the output on the intended device before deleting the original.

This method can be used free without installing software. Conversion normally re-encodes the streams, so the output may differ in size, quality, subtitle tracks, and available audio tracks from the source.

Desktop conversion with HandBrake

1. Open the MKV in HandBrake with Open Source.
2. On the Summary tab, set Format to MP4.
3. Choose a preset close to the target resolution, then open the Video tab and select Video Encoder → H.264 (x264).
4. On the Audio tab, select Codec → AAC for each audio track that must be retained.
5. Set an output filename ending in .mp4 and select Start Encode.

HandBrake's Constant Quality setting controls the size-versus-quality trade-off. For H.264, RF 18–20 is a reasonable starting range for high-quality HD output; higher RF values produce smaller files with more compression. Test a short sample when file size or quality is critical.

FFmpeg commands

This command re-encodes the first video stream as H.264 and keeps available audio streams as AAC:

ffmpeg -i input.mkv -map 0:v:0 -map 0:a? -c:v libx264 -crf 20 -preset medium -c:a aac -b:a 192k -movflags +faststart output.mp4

Lower -crf values increase quality and file size. -movflags +faststart moves MP4 indexing data to the beginning of the file, which helps progressive web playback.

If the source already has H.264 video and AAC audio, changing only the container avoids re-encoding and quality loss:

ffmpeg -i input.mkv -map 0:v:0 -map 0:a? -c copy -movflags +faststart output.mp4

Stream copying is fast, but it does not make HEVC, DTS, Opus, or other unsupported source streams compatible with an older device. It can also fail when an audio or video stream cannot be stored in MP4.

Compatibility limits

Re-encoding introduces a new lossy compression pass; an MP4 is not automatically smaller or better-looking than the MKV source. File size depends on the selected codec, quality setting, resolution, frame rate, audio bitrate, and source complexity.

MKV subtitle support is broader than MP4 subtitle support. Text subtitles may be converted to MP4 mov_text tracks, while image-based PGS and VobSub subtitles generally need to be burned into the video for reliable MP4 playback. Burning subtitles makes them permanent and can require video re-encoding.

For older hardware, use H.264 video, AAC audio, an .mp4 extension, and a resolution and frame rate supported by the target device. Preserve the original MKV if it contains extra audio, chapters, attachments, or subtitles that the MP4 output does not retain.