exiftool no elimina los metadatos de los MP4 (cosas como "Promotion URL" y "Author URL")

Tengo un archivo MP4 con URI de anuncios en los metadatos. Deseo eliminarlos:

exiftool example.mp4
ExifTool Version Number         : 10.40
File Name                       : example.mp4
Directory                       : .
File Size                       : 12 MB
File Modification Date/Time     : 2017:03:19 06:53:08+01:00
File Access Date/Time           : 2017:03:19 06:53:08+01:00
File Inode Change Date/Time     : 2017:03:19 06:53:08+01:00
File Permissions                : rw-r--r--
File Type                       : MP4
File Type Extension             : mp4
MIME Type                       : video/mp4
Major Brand                     : MP4  Base Media v1 [IS0 14496-12:2003]
Minor Version                   : 0.2.0
Compatible Brands               : isom, iso2, avc1, mp41
Movie Data Size                 : 12077146
Movie Data Offset               : 11050
Movie Header Version            : 0
Create Date                     : 0000:00:00 00:00:00
Modify Date                     : 0000:00:00 00:00:00
Time Scale                      : 1000
Duration                        : 0:00:30
Preferred Rate                  : 1
Preferred Volume                : 100.00%
Preview Time                    : 0 s
Preview Duration                : 0 s
Poster Time                     : 0 s
Selection Time                  : 0 s
Selection Duration              : 0 s
Current Time                    : 0 s
Next Track ID                   : 3
Track Header Version            : 0
Track Create Date               : 0000:00:00 00:00:00
Track Modify Date               : 2016:12:09 04:26:57
Track ID                        : 1
Track Duration                  : 0:00:30
Track Layer                     : 0
Track Volume                    : 0.00%
Image Width                     : 360
Image Height                    : 640
Graphics Mode                   : srcCopy
Op Color                        : 0 0 0
Compressor ID                   : avc1
Source Image Width              : 360
Source Image Height             : 640
X Resolution                    : 72
Y Resolution                    : 72
Bit Depth                       : 24
Video Frame Rate                : 29.97
Matrix Structure                : 1 0 0 0 1 0 0 0 1
Media Header Version            : 0
Media Create Date               : 0000:00:00 00:00:00
Media Modify Date               : 0000:00:00 00:00:00
Media Time Scale                : 44100
Media Duration                  : 0:00:30
Media Language Code             : und
Handler Type                    : Audio Track
Handler Description             : SoundHandler
Balance                         : 0
Audio Format                    : mp4a
Audio Channels                  : 2
Audio Bits Per Sample           : 16
Audio Sample Rate               : 44100
Subtitle                        : example.com
Promotion URL                   : example.com
Author URL                      : example.com
Category                        : example.com
Avg Bitrate                     : 3.17 Mbps
Image Size                      : 360x640
Megapixels                      : 0.230
Rotation                        : 0

He intentado

exiftool -all= example.mp4
    1 image files updated

Pero no funcionó, el URI sigue en MP4.