I have only .stem.m4a and no originals

Question: I only have .stem.m4a files in my collection and no originals. What should I do? Should I use natively linked STEMS in Traktor Pro 4?

If you only have .stem.m4a files (created in NUO-STEMS 3 or NUO-STEMS 4) in your collection and no original tracks, you have a few options:

Option 1: Re-convert existing .stem.m4a files

You can re-convert your existing .stem.m4a files to NUO-STEMS 4 .stem.m4a files using Legacy / Export Mode. The main benefit you'll get is improved STEMS quality thanks to the new algorithms in NUO-STEMS 4.

This also means that you're essentially treating .stem.m4a files as first class citizens.
You remove all original tracks from your collection, and only keep .stem.m4a files.

Keep in mind that after you re-convert your existing NUO-STEMS 3 .stem.m4a files to NUO-STEMS 4 .stem.m4a files, they won't be compatible with Traktor Pro 3.

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Upon my testing, AUDIO_ID of the new .stem.m4a (created in NUO-STEMS 4) shall be the same as previous .stem.m4a (created in NUO-STEMS 3). So you can potentially replace existing .stem.m4a files in-place. However, I would advise to check at least a few files to make sure that everything is working correctly.

Also, it's always a good idea to backup your collection & files before doing any major changes.

NUO-STEMS 4 will also make sure to output correct filename (e.g. song.stem.m4a will be converted to song.stem.m4a).

Previously (in NUO-STEMS 3) there was a bug where .stem.m4a files had duplicated .stem.stem.m4a ending if re-converted.

Option 2: Migrate to Traktor Pro 4 approach

If you want to migrate to the Traktor Pro 4 approach with both originals and "linked native" stems in your collection,
BUT you only have .stem.m4a files in collection and no originals:

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Currently, there is no straight-forward way to do this. Proceed with caution.

If you still want to proceed with migration, you need to:

1. Add originals to your collection.
2. Analyze all originals in TP4 (no need to set hotcues).
3. Close Traktor Pro 4.
4. Open NUO-STEMS 3 (not NUO-STEMS 4) and go to Settings > Traktor Utilities.
5. Change "Transfer direction" to "STEMS to Original".
6. Go to "Traktor Utilities" tab and click "Sync All".
7. Now you have both originals and .stem.m4a stems in your collection synced. Originals shall have correct colors, hotcues, beatgrids, etc.
   1. warning

      I would advice to check at least few originals to make sure that everything is synced correctly.

8. Delete all .stem.m4a files from your collection.
9. Prooceed with generating new "linked native" stems from the originals using NUO-STEMS 4.