# Multivalued fields for AAC?

**URL:** https://community.mp3tag.de/t/multivalued-fields-for-aac/68857
**Category:** Support
**Created:** [June 13, 2025, 7:03pm UTC](https://community.mp3tag.de/t/multivalued-fields-for-aac/68857 "2025-06-13T19:03:13Z")
**Posts on this page:** 1
**Showing post:** 5

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### Author: ![Florian](https://community.mp3tag.de/user_avatar/community.mp3tag.de/florian/32/5759_2.png) [@Florian](https://community.mp3tag.de/u/Florian)
#### Post date: [June 14, 2025, 6:39am UTC](https://community.mp3tag.de/t/multivalued-fields-for-aac/68857/5 "2025-06-14T06:39:23Z")

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Yes, there are actually three different ways of properly storing multiple values in MP4.

1. **Flatten multiple values**  
This is the most compatible approach, albeit not really multi-value. Here, multiple values are written in one field, separated by a character or character sequence, e.g., `;`, `,`, or `/`

```auto
aART...data...Album Artist 1 Name;Album Artist 2 Name

```

1. **Write one MP4 atom per value**  
This is the approach Mp3tag and others have taken. Each value is stored in one MP4 atom, e.g., `aART` for `ALBUMARTIST` with a `data` part that keeps the actual name of the album artist.

```auto
aART...data...Album Artist 1 Name
aART...data...Album Artist 2 Name

```

1. **Write one MP4 atom with multiple data parts**  
This is the approach Navidrome is using. Individual values are stored in multiple `data` atoms that are contained in the MP4 atom for the actual field.

```auto
aART...data...Album Artist 1 Name...data...Album Artist 2 Name

```

* * *

All this happened, because there is no clear standard on how multiple values are stored. iTunes / Apple Music doesn't really support multiple values as in 2. and 3., so different implementations came up with different ways of dealing with multiple values.

**Mp3tag supports reading all three different variants** (which I'd recommend for any application that reads metadata from MP4) and currently supports writing variants 1. and 2.

Since variants 2. and 3. are mutually exclusive, a dedicated configuration setting would be needed.

I'll keep you posted.

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_[View the full topic](https://community.mp3tag.de/t/multivalued-fields-for-aac/68857)._