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 http://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

Hi,

I built `gpac` twice with `gcc-11 -O0` and `gcc-11 -O3` separately. For the provided input, `MP4Box -bt` would produce different outputs/warnings. Reproduce as follows:
- Compile  `gpac` twice with `gcc-11 -O0` and `gcc-11 -O3` to obtain two versions MP4Box: `MP4Box-O0` and `MP4Box-O3`
- Run `MP4Box-O0 -bt $issue-2130 -std > out-O0.txt 2>&1` and `MP4Box-O3 -bt $issue-2130 -std > out-O3.txt 2>&1`
- Compare with `diff -y out-O0.txt out-O3.txt` and you'll see these two files differ (`out-O3.txt` shown on the right has two more lines than `out-O1.txt`) 
[issue-2130.tar.gz](https://github.com/gpac/gpac/files/8171226/issue-2130.tar.gz)

```
[33m[ISO file] dataReferenceIndex set to 0 in sample entry, o	[33m[ISO file] dataReferenceIndex set to 0 in sample entry, o
[isom/avcc] Missing REXT profile signaling, patching.	[isom/avcc] Missing REXT profile signaling, patching.
[iso file] Missing DataInformationBox			[iso file] Missing DataInformationBox
[iso file] Box "saiz" (start 1128) has 8 extra bytes	[iso file] Box "saiz" (start 1128) has 8 extra bytes
[iso file] Warning: trackID of MOOF/TRAF(2) is not the	[iso file] Warning: trackID of MOOF/TRAF(2) is not the
							      >	[iso file] saiz box without flags nor aux info type an
[iso file] senc box without tenc, assuming MS smooth+p	[iso file] senc box without tenc, assuming MS smooth+p
[isobmf] cannot parse senc, missing IV/crypto state	[isobmf] cannot parse senc, missing IV/crypto state
[iso file] Unknown top-level box type D2E498FF		[iso file] Unknown top-level box type D2E498FF
[iso file] Incomplete box D2E498FF - start 1965 size 1	[iso file] Incomplete box D2E498FF - start 1965 size 1
[iso file] Incomplete file while reading for dump - ab	[iso file] Incomplete file while reading for dump - ab
[ISO file] dataReferenceIndex set to 0 in sample entry	[ISO file] dataReferenceIndex set to 0 in sample entry
[isom/avcc] Missing REXT profile signaling, patching.	[isom/avcc] Missing REXT profile signaling, patching.
[iso file] Missing DataInformationBox			[iso file] Missing DataInformationBox
[iso file] Box "saiz" (start 1128) has 8 extra bytes	[iso file] Box "saiz" (start 1128) has 8 extra bytes
[iso file] Warning: trackID of MOOF/TRAF(2) is not the	[iso file] Warning: trackID of MOOF/TRAF(2) is not the
							      >	[iso file] saiz box without flags nor aux info type an
[iso file] senc box without tenc, assuming MS smooth+p	[iso file] senc box without tenc, assuming MS smooth+p
[isobmf] cannot parse senc, missing IV/crypto state	[isobmf] cannot parse senc, missing IV/crypto state
[iso file] Unknown top-level box type D2E498FF		[iso file] Unknown top-level box type D2E498FF
[iso file] Incomplete box D2E498FF - start 1965 size 1	[iso file] Incomplete box D2E498FF - start 1965 size 1
[iso file] Incomplete file while reading for dump - ab	[iso file] Incomplete file while reading for dump - ab
Scene loaded - dumping root scene				Scene loaded - dumping root scene
```

 
Incorrect/inconsistent results produced by `MP4Box -bt` because of uninitialized variable `scheme_type ` in track.c
This is a GitHub Issue
repo:gpac
owner:gpac
Title : Incorrect/inconsistent results produced by `MP4Box -bt` because of uninitialized variable `scheme_type ` in track.c
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. Installers available at http://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

Hi,

I built `gpac` twice with `gcc-11 -O0` and `gcc-11 -O3` separately. For the provided input, `MP4Box -bt` would produce different outputs/warnings. Reproduce as follows:
- Compile  `gpac` twice with `gcc-11 -O0` and `gcc-11 -O3` to obtain two versions MP4Box: `MP4Box-O0` and `MP4Box-O3`
- Run `MP4Box-O0 -bt $issue-2130 -std > out-O0.txt 2>&1` and `MP4Box-O3 -bt $issue-2130 -std > out-O3.txt 2>&1`
- Compare with `diff -y out-O0.txt out-O3.txt` and you'll see these two files differ (`out-O3.txt` shown on the right has two more lines than `out-O1.txt`) 
[issue-2130.tar.gz](https://github.com/gpac/gpac/files/8171226/issue-2130.tar.gz)

```
[33m[ISO file] dataReferenceIndex set to 0 in sample entry, o	[33m[ISO file] dataReferenceIndex set to 0 in sample entry, o
[isom/avcc] Missing REXT profile signaling, patching.	[isom/avcc] Missing REXT profile signaling, patching.
[iso file] Missing DataInformationBox			[iso file] Missing DataInformationBox
[iso file] Box "saiz" (start 1128) has 8 extra bytes	[iso file] Box "saiz" (start 1128) has 8 extra bytes
[iso file] Warning: trackID of MOOF/TRAF(2) is not the	[iso file] Warning: trackID of MOOF/TRAF(2) is not the
							      >	[iso file] saiz box without flags nor aux info type an
[iso file] senc box without tenc, assuming MS smooth+p	[iso file] senc box without tenc, assuming MS smooth+p
[isobmf] cannot parse senc, missing IV/crypto state	[isobmf] cannot parse senc, missing IV/crypto state
[iso file] Unknown top-level box type D2E498FF		[iso file] Unknown top-level box type D2E498FF
[iso file] Incomplete box D2E498FF - start 1965 size 1	[iso file] Incomplete box D2E498FF - start 1965 size 1
[iso file] Incomplete file while reading for dump - ab	[iso file] Incomplete file while reading for dump - ab
[ISO file] dataReferenceIndex set to 0 in sample entry	[ISO file] dataReferenceIndex set to 0 in sample entry
[isom/avcc] Missing REXT profile signaling, patching.	[isom/avcc] Missing REXT profile signaling, patching.
[iso file] Missing DataInformationBox			[iso file] Missing DataInformationBox
[iso file] Box "saiz" (start 1128) has 8 extra bytes	[iso file] Box "saiz" (start 1128) has 8 extra bytes
[iso file] Warning: trackID of MOOF/TRAF(2) is not the	[iso file] Warning: trackID of MOOF/TRAF(2) is not the
							      >	[iso file] saiz box without flags nor aux info type an
[iso file] senc box without tenc, assuming MS smooth+p	[iso file] senc box without tenc, assuming MS smooth+p
[isobmf] cannot parse senc, missing IV/crypto state	[isobmf] cannot parse senc, missing IV/crypto state
[iso file] Unknown top-level box type D2E498FF		[iso file] Unknown top-level box type D2E498FF
[iso file] Incomplete box D2E498FF - start 1965 size 1	[iso file] Incomplete box D2E498FF - start 1965 size 1
[iso file] Incomplete file while reading for dump - ab	[iso file] Incomplete file while reading for dump - ab
Scene loaded - dumping root scene				Scene loaded - dumping root scene
```

 
--- end body ---

The issue indicates that the `MP4Box -bt` command produces inconsistent results due to the use of an uninitialized variable `scheme_type` in the `track.c` file. This can lead to undefined behavior, which may potentially be exploited to cause incorrect processing of media files, although it does not directly indicate a security vulnerability. The inconsistency in output could lead to confusion or misuse of the tool, but it does not appear to expose any sensitive data or allow for malicious actions.