Muxing is the process of combining audio/video streams into a container such as mp4.
Depending on the protocol being captured this will always need to happen.
The time taken to mux depends on:
1. The amount of data to be muxed (size of the download);
2. The audio and video codecs captured from the stream and if they need to be converted to something the output container supports;
3. The number of concurrent downloads and thus muxing you have happening at the same time;
4. The resources available on your computer (memory/cpu/disk speed etc).
There are various things you can do to improve performance:
1. Limit the number of concurrent downloads in the settings.
Go to Settings > Internet Downloads
2. For HLS protocol streams.
Go to Settings > Internet Downloads > Advanced > HLS
If your are using the HLSD downloader you can configure the mux to Raw and convert later. No mux will then happen when the download is complete. The resultant raw file can then be converted later using JMR's built in converter. Most though should still play using VLC or Jaksta Media Player.
If using ffmpeg as the downloader, then the muxing is effectively happening as the download happens. Switching off MPG output can speed things up even more. Output will be in raw format, but again most should still play using VLC or Jaksta Media Player and conversions can be done later using JMR's built in converter.
3. Switch of MP4 fast start muxing
Go to Settings > Internet Downloads > Advanced > Mux
When MP4 Fast Start is on, a second pass is done on the file when muxing which moves the index to the start of the file.
Switching it off will make the mux faster but, depending on the player used when playing the video, it may trigger an unsupported file message or similar from the player or may take a considerable time to start playing.
4. If the streams are ones captured by the monitor or a scheduled recording, then configure the monitor or schedule to split at set intervals.
This is done on the Split tab of the monitor or schedule and will result in smaller downloads and thus make muxing faster as it is processing less data.
5. Try different versions of ffmpeg
JMR distributes the excellent open source ffmpeg to perform muxing. FFmpeg has always been a very experimental and developer-driven project. It is a key component in many multimedia products and has new features added constantly.
You can download versions of ffmpeg by following one of the windows build links from https://ffmpeg.org/download.html. Id recommend release builds from https://www.gyan.dev/ffmpeg/builds/#release-builds
Replace the ffmpeg.exe in the JMR install folder with which ever version you descide to download.