After conversion, you can quickly inspect the MKV container:
ffprobe -i output_file.mkv -show_streams -loglevel error
Or, simply open the file in VLC → Tools → Codec Information to see the track list.
| Symptom | Likely Cause | Fix |
|---------|--------------|-----|
| “Unsupported codec” error | Input contains a codec not directly compatible with MKV. | Add -c to force re‑encoding, optionally specify a preset (-p fast). |
| “File not found” | Wrong path or typo. | Verify the path with dir (Windows) or ls (macOS/Linux). Use quotes if the path contains spaces. |
| Conversion is very slow | Large source file + re‑encoding on a low‑powered CPU. | Omit -c if you can keep streams as‑is, or use a faster preset (-p fast). |
| Output video has no audio | Audio track was excluded inadvertently. | Ensure you didn’t use -s none and check track IDs with niks2mkv -i input.niks. |
| MKV won’t play in player | Corrupt output (e.g., incomplete write due to disk space). | Verify enough free disk space, run with --dry-run first, and try playing the file with VLC (which provides detailed error messages). |
niks2mkv "C:\Videos\myrecording.niks" -o "C:\Videos\myrecording.mkv"
or, on macOS / Linux:
niks2mkv ~/Downloads/lecture.niks -o ~/Downloads/lecture.mkv
| Question | Answer |
|----------|--------|
| Do I need to install any codecs? | No. niks2mkv ships with built‑in demuxers for NIKS. It can copy existing streams directly, so no extra codecs are required unless you force re‑encoding. |
| Can I preserve chapter marks? | Yes. If the source NIKS file contains chapter metadata, it is automatically transferred to the MKV file. |
| Is there a GUI? | The official distribution is CLI‑only, but third‑party wrappers (e.g., “Niks2Mkv GUI”) exist. You can also create a simple batch file or shell script to hide the command line. |
| What about subtitles that are embedded as images? | They are carried over unchanged. If you need them as text, extract with niks2mkv -t subtitles and run an OCR step separately. |
| Can I merge multiple NIKS files into one MKV? | Yes – concatenate them first using cat file1.niks file2.niks > combined.niks (Linux/macOS) or type file1.niks file2.niks > combined.niks (Windows) and then run niks2mkv combined.niks. |