GPAC uses a configuration file to modify default options of libgpac and filters. This file is called GPAC.cfg and is located:

• on Windows platforms, in C:\Users\FOO\AppData\Roaming\GPAC or in C:\Program Files\GPAC.
• on iOS platforms, in a .gpac folder in the app storage directory.
• on Android platforms, in /sdcard/GPAC/ if this directory exists, otherwise in /data/data/io.gpac.gpac/GPAC.
• on other platforms, in a $HOME/.gpac/.

Applications in GPAC can also specify a different configuration file through the -p profile option. EX gpac -p=foo []
This will load configuration from $HOME/.gpac/foo/GPAC.cfg, creating it if needed.
The reserved name 0 is used to disable configuration file writing.

The configuration file is structured in sections, each made of one or more keys:

• section foo is declared as [foo]\n
• key bar with value N is declared as bar=N\n. The key value N is not interpreted and always handled as ASCII text.

By default the configuration file only holds a few system specific options and directories. It is possible to serialize the entire set of options to the configuration file, using -wc -wf.
This should be avoided as the resulting configuration file size will be quite large, hence larger memory usage for the applications.
The options specified in the configuration file may be overridden by the values in restrict.cfg file located in GPAC share system directory (e.g. /usr/share/gpac or C:\Program Files\GPAC), if present; this allows enforcing system-wide configuration values.
Note: The methods describe in this section apply to any application in GPAC transferring their arguments to libgpac. This is the case for gpac and MP4Box.

The options from libgpac core can also be assigned though the config file from section core using option name without initial dash as key name.
Example

[core]  
threads=2

Setting this in the config file is equivalent to using -threads=2.
The options specified at prompt overrides the value of the config file.

It is possible to alter the default value of a filter option by modifying the configuration file. Filter foo options are stored in section [filter@foo], using option name and value as key-value pair. Options specified through the configuration file do not take precedence over options specified at prompt or through alias.
Example

[filter@rtpin]  
interleave=yes

This will force the rtp input filter to always request RTP over RTSP by default.
To generate a configuration file with all filters options serialized, use -wf.

It is possible to specify options global to multiple filters using --OPTNAME=VAL. Global options do not override filter options but take precedence over options loaded from configuration file.
This will set option OPTNAME, when present, to VAL in any loaded filter.
Example

--buffer=100 -i file vout aout

This is equivalent to specifying vout:buffer=100 aout:buffer=100.
Example

--buffer=100 -i file vout aout:buffer=10

This is equivalent to specifying vout:buffer=100 aout:buffer=10.

Warning: This syntax only applies to regular filter options. It cannot be used with builtin shortcuts (gfreg, enc, ...).

Meta-filter options can be set in the same way using the syntax --OPT_NAME=VAL.
Example

--profile=Baseline -i file.cmp -o dump.264

This is equivalent to specifying -o dump.264:profile=Baseline.

For both syntaxes, it is possible to specify the filter registry name of the option, using --FNAME:OPTNAME=VAL or --FNAME@OPTNAME=VAL.
In this case the option will only be set for filters which are instances of registry FNAME. This is used when several registries use same option names.
Example

--flist@timescale=100 -i plist1 -i plist2 -o live.mpd

This will set the timescale option on the playlists filters but not on the dasher filter.