Convert MKV files to AVI on Windows
On Windows computers I highly recommend using Video to Video Converter. It is an excellent free converter that supports all the most common video file formats (not only MKV and AVI, but also MP4, WMV, MOV and many more) and works without requiring installation: you download, start and use !
To download the program on your PC, connect to its official website and first click on the button Download and then on the voice Click here to download ZIP archive. After that open the zip archive which contains Video to Video Converter (VTV.zip), extract the contents to a folder of your choice and run the executable vv.exe.
Nella finestra che si apre, scegli l 'cittàn from the drop-down menu for language selection, click on the button OK and drag MKV videos you want to convert to AVI into the software window. A screen will open with the list of all available output formats and all the options to customize the conversion parameters.
Then click on the icon REVIEWS and carefully check the settings contained in the right sidebar: make sure that in the field Quality the wording is shown Same as source, than in the field Video size the item is set Original (so that the resolution and quality of the video are the same as those of the source video) and, if the MKV file you are about to convert contains more than one audio track, choose which one to keep in the video in AVI format by selecting a number from the field Audio stream index (Eg. 0 for the main audio track, 1 for the secondary one, and so on).
If you want to add subtitles to the output video, click on the button [...] placed next to the item Subtitle file (still in the right sidebar) and select an external SRT file. Unfortunately it is not possible to imprint the subtitles contained in the MKV file directly on the video, but there is a way to extract them and use them as external SRT files: I will tell you about it in the final part of this tutorial.
Once all the conversion parameters have been adjusted, press the button OK, choose the folder in which to save the output files by clicking on the icon folder located at the bottom right and start the video conversion process by clicking on the button Converted (top left).
Convert MKV files to AVI on Mac
If you have a Mac, you can convert MKV to AVI with Adapter, a free all-in-one converter characterized by extreme ease of use and the presence of numerous interesting functions. It also allows you to subtitle videos using external SRT files, but unfortunately it does not allow you to choose the audio track to keep in multi-track MKVs (it automatically keeps the primary one).
To download Adapter on your computer, connect to the program site and press the button Download. Then open the package dmg that contains the software and drag the icon it contains into the folder Applications in OS X.
When the operation is complete, start the program, click on the button Continue present in the window that opens and wait for it to be downloaded from the Internet (and then installed) FFMPEG, a free software necessary for the operation of the converter.
Once the download is complete, drag the MKV videos to convert to AVI into the Adapter window and select the option Video> General> Custom AVI from the drop-down menu located at the bottom. Next, click on thegear to bring up the panel with the application settings and choose the item Same as source in the field Resolution (in order to keep the native resolution of the video).
Next, set the entry High o Very high give menu to tendin Quality (in order to get a high quality AVI file); add, if you want, an external subtitle file by dragging it into the field Layers, and start the conversion process by pressing the button Convert.
How to extract subtitles from MKV videos
If you want to extract subtitles from MKV file to use as external SRT files  or imprint them on AVI format videos, use the following free applications.
- MKVToolnix / MKVExtractGUI - it is a pair of free software for Windows. The first serves only as the "engine" of the second, which must actually be used. To download them to your PC, visit the links I just provided you and click on the items Download MKVToolnix 7.9.0 portable 64-bit (direct link) (Or Download MKVToolnix 7.9.0 portable (direct link) if you are using a 32-bit operating system) e Download MKVExtractGUI-2 220.127.116.11 (direct link). After that extract both software in the same folder and launch the executable MKVExtractGUI2.exe. In the window that opens, put the check mark next to the subtitle tracks (subtitles) that you intend to extract and press the button Extract but I will complete the operation.
- MKVTools - Mac application with functions similar to MKVToolnix (although less complete and alas less stable). It is free but often invites the user to register the copy of the software by paying a sum of $ 5. To download it to your computer, visit the link I just provided and click on the item Download MKVtools 3.4.5 (direct link). When the download is complete, open the dmg package that contains the program and drag the icon it contains into the folder Applications of OS X. Next, start MKVTools, press the buttons Open e Register later and select the MKV file from which to extract subtitles, put the check mark next to the subtitle tracks (subtitle) that you intend to extract and press the button Extract but I will complete the operation.
- To use external subtitles, just copy them to the same folder as the video and rename them as the latter. Most players and devices can detect them automatically. ↩