Hello,
I need to extract some additional data (GoPro GPS data) from a MP4 file and add them to another MP4 file.
I'm able to extract them with the command
`mp4box.exe -raw 3 ..\video.mp4`

But when I try to import them again with this command
`mp4box.exe -add ..\GoproVideo.mp4 -set-meta meta:tk=3 -add-item ..\video_track3.gpmd:tk=3 -new output.mp4`

I got the following error
`Trying to add item, but missing meta box`

Am I missing something? Looking at the documentation, command line seems ok because I set the meta type and then add the item to it. Should I create first the track3? Or is automatically created with the set-meta command?

This is what I get if I run a -info on the original file
```
# Track 3 Info - ID 3 - TimeScale 1000
Media Duration 00:14:41.526
Track has 2 edits: track duration is 00:14:41.628
Track flags: Enabled In Movie In Preview
Media Samples: 8801
1 UDTA types:
        meta:
Media Type: meta:gpmd
        Unknown Metadata Stream
        RFC6381 Codec Parameters: gpmd
        All samples are sync
        Max sample duration: 104 / 1000
```


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. Installers available at https://gpac.io/downloads/gpac-nightly-builds/
- [x] I give enough information for contributors to reproduce my issue (meaningful title, github labels, platform and compiler, command-line ...). I can share files anonymously with this dropbox: https://www.mediafire.com/filedrop/filedrop_hosted.php?drop=eec9e058a9486fe4e99c33021481d9e1826ca9dbc242a6cfaab0fe95da5e5d95

Detailed guidelines: https://gpac.io/bug-reporting/

"Trying to add item, but missing meta box" error
This is a GitHub Issue
repo:gpac
owner:gpac
Title : "Trying to add item, but missing meta box" error
Issue date:

--- start body ---
Hello,
I need to extract some additional data (GoPro GPS data) from a MP4 file and add them to another MP4 file.
I'm able to extract them with the command
`mp4box.exe -raw 3 ..\video.mp4`

But when I try to import them again with this command
`mp4box.exe -add ..\GoproVideo.mp4 -set-meta meta:tk=3 -add-item ..\video_track3.gpmd:tk=3 -new output.mp4`

I got the following error
`Trying to add item, but missing meta box`

Am I missing something? Looking at the documentation, command line seems ok because I set the meta type and then add the item to it. Should I create first the track3? Or is automatically created with the set-meta command?

This is what I get if I run a -info on the original file
```
# Track 3 Info - ID 3 - TimeScale 1000
Media Duration 00:14:41.526
Track has 2 edits: track duration is 00:14:41.628
Track flags: Enabled In Movie In Preview
Media Samples: 8801
1 UDTA types:
        meta:
Media Type: meta:gpmd
        Unknown Metadata Stream
        RFC6381 Codec Parameters: gpmd
        All samples are sync
        Max sample duration: 104 / 1000
```


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. Installers available at https://gpac.io/downloads/gpac-nightly-builds/
- [x] I give enough information for contributors to reproduce my issue (meaningful title, github labels, platform and compiler, command-line ...). I can share files anonymously with this dropbox: https://www.mediafire.com/filedrop/filedrop_hosted.php?drop=eec9e058a9486fe4e99c33021481d9e1826ca9dbc242a6cfaab0fe95da5e5d95

Detailed guidelines: https://gpac.io/bug-reporting/

--- end body ---
