<!-- 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

<!-- Detailed guidelines: http://gpac.io/2013/07/16/how-to-file-a-bug-properly/ -->

### Environment
~~~
C:\>MP4Box -version
MP4Box - GPAC version 1.1.0-DEV-rev540-g741a7d1a-master
(c) 2000-2021 Telecom Paris distributed under LGPL v2.1+

Please cite our work in your research:
        GPAC Filters: https://doi.org/10.1145/3339825.3394929
        GPAC: https://doi.org/10.1145/1291233.1291452

GPAC Configuration: (static configuration file)
Features: GPAC_CONFIG_WIN32 GPAC_64_BITS GPAC_MEMORY_TRACKING GPAC_HAS_SSL GPAC_MINIMAL_ODF GPAC_HAS_QJS GPAC_HAS_FAAD GPAC_HAS_MAD GPAC_HAS_LIBA52 GPAC_HAS_JPEG GPAC_HAS_PNG GPAC_HAS_FFMPEG GPAC_HAS_OPENSVC GPAC_HAS_JP2 GPAC_HAS_OPENHEVC GPAC_HAS_THEORA GPAC_HAS_VORBIS GPAC_HAS_XVID GPAC_HAS_GLU
~~~


### Steps to reproduce

~~~
MP4Box -lf GOPR0178-mp4box-bug-log.txt -logs all@debug -split-size 51200 GOPR0178.MP4
~~~

#### Actual result

~~~
C:\>MP4Box -lf GOPR0178-mp4box-bug-log.txt -logs all@debug -split-size 51200 GOPR0178.MP4
[Console] Detected Windows shell, will use SetConsoleTextAttribute for coloring
[Core] Open file GOPR0178-mp4box-bug-log.txt in mode wt
[Core] file "GOPR0178-mp4box-bug-log.txt" opened in mode "wt" - 1 file handles
~~~

[GOPR0178-mp4box-bug-log.txt](https://github.com/gpac/gpac/files/6073276/GOPR0178-mp4box-bug-log.txt)

Every output file has the same duration as the input file:

![actual](https://user-images.githubusercontent.com/9609370/109743685-b2b6c280-7c03-11eb-91a0-b571e8325971.png)

#### Expected result

The sum of durations of all output files equals to the duration of the input file:

![expected](https://user-images.githubusercontent.com/9609370/109743884-fc071200-7c03-11eb-822f-88f3dfc1db02.png)

### Additional information

`ffmpeg` works OK:
~~~
ffmpeg -i GOPR0178.MP4 -codec copy -ss 00:00:00 -fs 52428800 GOPR0178_001.MP4
ffmpeg -i GOPR0178.MP4 -codec copy -ss 00:00:13 -fs 52428800 GOPR0178_002.MP4
~~~



MP4Box sets wrong output duration when splits some files [bug]
This is a GitHub Issue
repo:gpac
owner:gpac
Title : MP4Box sets wrong output duration when splits some files [bug]
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

<!-- Detailed guidelines: http://gpac.io/2013/07/16/how-to-file-a-bug-properly/ -->

### Environment
~~~
C:\>MP4Box -version
MP4Box - GPAC version 1.1.0-DEV-rev540-g741a7d1a-master
(c) 2000-2021 Telecom Paris distributed under LGPL v2.1+

Please cite our work in your research:
        GPAC Filters: https://doi.org/10.1145/3339825.3394929
        GPAC: https://doi.org/10.1145/1291233.1291452

GPAC Configuration: (static configuration file)
Features: GPAC_CONFIG_WIN32 GPAC_64_BITS GPAC_MEMORY_TRACKING GPAC_HAS_SSL GPAC_MINIMAL_ODF GPAC_HAS_QJS GPAC_HAS_FAAD GPAC_HAS_MAD GPAC_HAS_LIBA52 GPAC_HAS_JPEG GPAC_HAS_PNG GPAC_HAS_FFMPEG GPAC_HAS_OPENSVC GPAC_HAS_JP2 GPAC_HAS_OPENHEVC GPAC_HAS_THEORA GPAC_HAS_VORBIS GPAC_HAS_XVID GPAC_HAS_GLU
~~~


### Steps to reproduce

~~~
MP4Box -lf GOPR0178-mp4box-bug-log.txt -logs all@debug -split-size 51200 GOPR0178.MP4
~~~

#### Actual result

~~~
C:\>MP4Box -lf GOPR0178-mp4box-bug-log.txt -logs all@debug -split-size 51200 GOPR0178.MP4
[Console] Detected Windows shell, will use SetConsoleTextAttribute for coloring
[Core] Open file GOPR0178-mp4box-bug-log.txt in mode wt
[Core] file "GOPR0178-mp4box-bug-log.txt" opened in mode "wt" - 1 file handles
~~~

[GOPR0178-mp4box-bug-log.txt](https://github.com/gpac/gpac/files/6073276/GOPR0178-mp4box-bug-log.txt)

Every output file has the same duration as the input file:

![actual](https://user-images.githubusercontent.com/9609370/109743685-b2b6c280-7c03-11eb-91a0-b571e8325971.png)

#### Expected result

The sum of durations of all output files equals to the duration of the input file:

![expected](https://user-images.githubusercontent.com/9609370/109743884-fc071200-7c03-11eb-822f-88f3dfc1db02.png)

### Additional information

`ffmpeg` works OK:
~~~
ffmpeg -i GOPR0178.MP4 -codec copy -ss 00:00:00 -fs 52428800 GOPR0178_001.MP4
ffmpeg -i GOPR0178.MP4 -codec copy -ss 00:00:13 -fs 52428800 GOPR0178_002.MP4
~~~



--- end body ---
