Free online ISMV to MKV converter

Some video players and editing applications do not recognize Microsoft Smooth Streaming files with the .ismv extension. Converting the container to .mkv makes the audio and video easier to archive, inspect, edit, or play without changing the streams when direct remuxing is supported.

What the ISMV format is

ISMV is a fragmented MP4 container used by Microsoft IIS Smooth Streaming. It commonly contains H.264 video and AAC audio divided into fragments for adaptive streaming, with metadata associated with a Smooth Streaming presentation. You may encounter ISMV files exported by Microsoft Expression Encoder, generated by IIS media workflows, or extracted from Smooth Streaming content alongside .isma audio files and a .ism server manifest.

What the MKV format is

MKV, or Matroska Video, is a flexible container for multiple video, audio, subtitle, chapter, and attachment tracks. It is useful for local playback and archival because it can hold common codecs without requiring them to be re-encoded, and it supports track selection, embedded subtitles, chapters, and metadata more flexibly than many streaming containers.

How to convert ISMV to MKV

Using FFmpeg

FFmpeg is the most reliable desktop method for a direct container conversion. Install FFmpeg, open a terminal in the folder containing the source file, and run:

ffmpeg -i input.ismv -map 0 -c copy output.mkv

-map 0 includes all detected streams, while -c copy copies them without decoding or quality loss. Replace input.ismv with the actual filename; quote the name if it contains spaces:

ffmpeg -i "Smooth Stream.ismv" -map 0 -c copy "Smooth Stream.mkv"

Check the result with FFmpeg or a player such as VLC:

ffprobe output.mkv

When direct copying fails

Some ISMV files are incomplete fragments, use an unusual codec, or contain timestamps that the Matroska muxer cannot interpret directly. First try generating the MKV with regenerated timestamps:

ffmpeg -fflags +genpts -i input.ismv -map 0 -c copy output.mkv

If the video or audio codec is unsuitable for the target player, re-encode only the incompatible stream. A broadly compatible option is:

ffmpeg -i input.ismv -map 0:v:0 -map 0:a? -c:v libx264 -crf 18 -preset medium -c:a aac -b:a 192k output.mkv

Re-encoding takes longer and changes the media quality; use stream copying whenever the original codecs are already supported.

Using the online converter

You can convert the file on 101convert.com for free without installing software. Upload the ISMV file, select MKV as the output format, start the conversion, and download the resulting file. Avoid uploading confidential or copyrighted material to any third-party service unless its use is permitted.

Quality, compatibility, and limitations

A successful -c copy conversion changes the container, not the encoded audio or video, so resolution, bitrate, frame rate, and quality remain unchanged. The output can still fail in a particular player if that player does not support the source codec, such as an uncommon MPEG-4 variant or a codec absent from the device.

An ISMV file may be only one fragment or may depend on an initialization segment and other fragments from the original Smooth Streaming package. FFmpeg cannot reconstruct missing media data; obtain the complete ISMV package before converting. If the source contains separate video and audio files rather than both streams in one file, provide both inputs and map them explicitly, for example:

ffmpeg -i video.ismv -i audio.isma -map 0:v:0 -map 1:a:0 -c copy combined.mkv