Thanks for reporting your issue. Please make sure these boxes are checked before submitting your issue - thank you!

- [X] I looked for a similar issue and couldn't find any.
- [X] I tried with the latest version of GPAC.
- [X] I give enough information for contributors to reproduce my issue _(Disclaimer: This is foremost a question.)_

I am experiencing some strange things when syncing video files ("Home Videos") from different Macs to an iPod Nano 3rd generation. Before syncing, the videos (on the Mac) have the following media information:

```
Media Type: sbtl:tx3g
	QT/3GPP subtitle
	Size 320 x 240 - Translation X=0 Y=0 - Layer 0
```

Curiously, after syncing from High Sierra (oldest macOS) and Ventura (newest macOS), the videos (on the iPod) have a modified media information. This causes the iPod not to display subtitles.

```
Media Type: gnrc:tx3g
	Subtitle/text 3GPP/Apple Stream
```

On Monterey (released between High Sierra and Ventura), media info is intact ("sbtl"), and subtitles are displayed.

My current workaround for High Sierra and Ventura is to stream copy the videos on the iPod, which reinstates `sbtl`.

Does anyone know what `gnrc` is, why it is applied by *some* macOS, and how to avoid this, in order to get subtitles? The `FOURCC` is elusive on the web and the gpac and FFmpeg sources. FFmpeg generates `sbtl` by default.

PS! Curiously, while "3GPP/Apple Stream" (associated with the obscure `gnrc`) occurs prominently in the MP4Box source, while "QT/3GPP" (associated with the more agreeable `sbtl`) is hardcoded.

https://github.com/gpac/gpac/blob/master/applications/mp4box/filedump.c#L3381

Ensuring subtitles on iPods ("sbtl" vs. "gnrc")
This is a GitHub Issue
repo:gpac
owner:gpac
Title : Ensuring subtitles on iPods ("sbtl" vs. "gnrc")
Issue date:

--- start body ---
Thanks for reporting your issue. Please make sure these boxes are checked before submitting your issue - thank you!

- [X] I looked for a similar issue and couldn't find any.
- [X] I tried with the latest version of GPAC.
- [X] I give enough information for contributors to reproduce my issue _(Disclaimer: This is foremost a question.)_

I am experiencing some strange things when syncing video files ("Home Videos") from different Macs to an iPod Nano 3rd generation. Before syncing, the videos (on the Mac) have the following media information:

```
Media Type: sbtl:tx3g
	QT/3GPP subtitle
	Size 320 x 240 - Translation X=0 Y=0 - Layer 0
```

Curiously, after syncing from High Sierra (oldest macOS) and Ventura (newest macOS), the videos (on the iPod) have a modified media information. This causes the iPod not to display subtitles.

```
Media Type: gnrc:tx3g
	Subtitle/text 3GPP/Apple Stream
```

On Monterey (released between High Sierra and Ventura), media info is intact ("sbtl"), and subtitles are displayed.

My current workaround for High Sierra and Ventura is to stream copy the videos on the iPod, which reinstates `sbtl`.

Does anyone know what `gnrc` is, why it is applied by *some* macOS, and how to avoid this, in order to get subtitles? The `FOURCC` is elusive on the web and the gpac and FFmpeg sources. FFmpeg generates `sbtl` by default.

PS! Curiously, while "3GPP/Apple Stream" (associated with the obscure `gnrc`) occurs prominently in the MP4Box source, while "QT/3GPP" (associated with the more agreeable `sbtl`) is hardcoded.

https://github.com/gpac/gpac/blob/master/applications/mp4box/filedump.c#L3381

--- end body ---
