An issue was discovered in GPAC version 0.8.0. There is a NULL pointer dereference in the function gf_isom_get_media_data_size() in isomedia/isom_read.c.
Thanks for reporting your issue. Please make sure these boxes are checked before submitting your issue - thank you!

- [ yes] I looked for a similar issue and couldn't find any.
- [ yes] I tried with the latest version of GPAC. Installers available at http://gpac.io/downloads/gpac-nightly-builds/
- [ yes] 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/

MP42TS -src $POC -dst-file /dev/null
[count_video.zip](https://github.com/gpac/gpac/files/4014701/count_video.zip)
asan output
```
root@ubuntu:/home/tim/gpac# ../gpac-asan/MP42TS -src crashes/count_video.mp4-signalb-0x0 -dst-file /dev/null
AddressSanitizer:DEADLYSIGNAL
=================================================================
==112791==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000028 (pc 0x55e4a53e12e4 bp 0x602000000370 sp 0x7fffdb37dbe0 T0)
==112791==The signal is caused by a READ memory access.
==112791==Hint: address points to the zero page.
    #0 0x55e4a53e12e3 in gf_isom_get_media_data_size isomedia/isom_read.c:3312
    #1 0x55e4a5391fdd in fill_isom_es_ifce /home/tim/gpac-asan/applications/mp42ts/main.c:620
    #2 0x55e4a5391fdd in open_source /home/tim/gpac-asan/applications/mp42ts/main.c:1518
    #3 0x55e4a53836c0 in parse_args /home/tim/gpac-asan/applications/mp42ts/main.c:2260
    #4 0x55e4a53836c0 in main /home/tim/gpac-asan/applications/mp42ts/main.c:2465
    #5 0x7f9a8b98ab6a in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x26b6a)
    #6 0x55e4a53899c9 in _start (/home/tim/gpac-asan/MP42TS+0x1249c9)

```

null pointer reference in  gf_isom_get_media_data_size
This is a GitHub Issue
repo:gpac
owner:gpac
Title : null pointer reference in  gf_isom_get_media_data_size
Issue date:

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

- [ yes] I looked for a similar issue and couldn't find any.
- [ yes] I tried with the latest version of GPAC. Installers available at http://gpac.io/downloads/gpac-nightly-builds/
- [ yes] 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/

MP42TS -src $POC -dst-file /dev/null
[count_video.zip](https://github.com/gpac/gpac/files/4014701/count_video.zip)
asan output
```
root@ubuntu:/home/tim/gpac# ../gpac-asan/MP42TS -src crashes/count_video.mp4-signalb-0x0 -dst-file /dev/null
AddressSanitizer:DEADLYSIGNAL
=================================================================
==112791==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000028 (pc 0x55e4a53e12e4 bp 0x602000000370 sp 0x7fffdb37dbe0 T0)
==112791==The signal is caused by a READ memory access.
==112791==Hint: address points to the zero page.
    #0 0x55e4a53e12e3 in gf_isom_get_media_data_size isomedia/isom_read.c:3312
    #1 0x55e4a5391fdd in fill_isom_es_ifce /home/tim/gpac-asan/applications/mp42ts/main.c:620
    #2 0x55e4a5391fdd in open_source /home/tim/gpac-asan/applications/mp42ts/main.c:1518
    #3 0x55e4a53836c0 in parse_args /home/tim/gpac-asan/applications/mp42ts/main.c:2260
    #4 0x55e4a53836c0 in main /home/tim/gpac-asan/applications/mp42ts/main.c:2465
    #5 0x7f9a8b98ab6a in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x26b6a)
    #6 0x55e4a53899c9 in _start (/home/tim/gpac-asan/MP42TS+0x1249c9)

```

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