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GPAC - MPEG-4 Systems Framework and Software Development Kit


GPAC stands (does it ?) for GPAC Project on Advanced Content. It is an implementation of
the MPEG-4 Systems standard written in ANSI C. GPAC provides tools for media playback,
vector graphics and 3D rendering, MPEG-4 authoring and distribution. This man page is
about configuration of the GPAC framework version 0.5.0.


Some applications in the GPAC framework use a configuration file shared among modules and
reloadable at run time. This file is located in the user home directory and called

The configuration file is based on the win32 .ini file model, ordered by sections and

A section is declared as [SectionName] , a key is declared as keyName=value , the key
value is not interpreted and always handled as ASCII text. Plugins may use the
configuration file as well (to avoid multiple files).

Note on plugin names: Plugin names as given in the configuration file are names exported
by each interface and not name of the physical library file (.dll/.so ...). The physical
file name can however be used to identify a plugin, it will be replaced by the interface
name if the plugin was successfully loaded.


The "General" section holds generic, OS and player specific options. This section is not
used by the GPAC Framework.

ModulesDirectory (value: path)
path to modules (plugins) location. The client cannot be loaded without modules.
This option is used by all GPAC clients on all platforms

CacheDirectory (value: path)
specifies location of temp files. This must be the absolute path to a directory
with write access. Although not used by applications, this is used by several

The following options are defined for Osmo4/wxWidgets player.

Loop (value: yes, no)
specifies whether the presentation has to be restarted when done playing.

ConsoleOff (value: yes, no)
specifies whether application messages (script, buffering, download progress) are
displayed in the console or not.

Browser (value: string)
specifies prefered browser for WWW anchors and scene graph viewing - Only used by

LookForSubtitles (value: yes, no)
specifies if Osmo4 shall look for subtitle files when opening a presentation.

PLEntry (value: unsigned int)
indicates active playlist entry when player was last closed. Playlist backup is
".gpac_pl.m3u", stored in user home directory.

StartupFile value: filename)
specifies file to load upon startup of osmo4/MP4Client. If not specified, no file
is loaded.

NoMIMETypeFetch (value: yes, no)
specifies if the player has to check for mime type when following hyperlinks, or
only follow links of known extensions.

LogFile (value: filename)
specifies where to output GPAC's log. By default, the logs are written to stdout.
Note that GPAC may be compiled without log support. This is not used by MP4Client.

LogLevel (value: none, error, warning, info, debug)
specifies the level of the log. By default, no log is performed.

LogTools (value: a ':'-separated list of the following values)
specifies which set of tools from GPAC should be logged. Available tools are:
core: libgpac core events.
coding: bitstream formats (audio, video, scene).
container: container formats (ISO File, MPEG-2 TS, AVI, ...).
network: network data exept RTP trafic.
rtp: rtp, rtcp and rtsp trafic.
author : authoring tools (hint, import, export).
sync: terminal sync layer.
codec: terminal codec messages.
parser: scene parsers (svg, xmt, bt) and other.
media: terminal media object management.
scene: scene graph and scene manager.
script: scripting engine messages.
compose: composition engine (events, etc).
render: renderng engine (2D, 3D, etc).
service: network service management.
mmio: Audio/Video HW I/O management.

SECTION RecentFiles

The "RecentFiles" section of the config file holds last accessed files (hardcoded to no
more than 20) in the last access order. The keys are the file names and no value is used.
This section is only used by GUI clients.


The "Systems" section holds all configuration options for the MPEG-4 Systems engine. The
following options are defined:

Language (value: 3-char code from ISO 639-2)
specifies the user prefered language. This is used to select streams in case of
alternate content in an audio object.

AlwaysDrawBIFS (value: yes, no)
if set, late BIFS frame will still be drawn. If not set, the scene won't be redrawn
until BIFS streams are back in sync. This is by default off to keep better sync,
but may be changed when testing heavy content or slow renderers.

ForceSingleClock (value: yes, no)
One big problem with MP4 files is that the notion of "duration" has been unclear
for a long time, and most content available (audio-video files) specifiy a wrong
BIFS duration. In such a case the movie cannot be controled/seek into.
Another problem with ISMA streaming is that BIFS/OD don't use the same clock as
audio/video, thus seeking the main timeline does not seek AV media.
Setting the ForceSingleClock will handle both cases by using a single timeline for
all media streams and setting the duration to the one of the longest stream.

ThreadingPolicy (value: Free, Single, Multi)
specifies how media decoders are to be threaded.
Free: lets decoders decide of their threading.
Single: means that all decoders are managed in a single thread performing
scheduling and priority handling.
Multi: means that each decoder runs in its own thread.

Priority (value: low, normal, high, real-time)
specifies the priority of the decoders (priority is applied to decoder thread(s)
regardless of threading mode).

hardcoded_protos (value: list of strings separated by space)
holds a list list of EXTERNPROTO URLs (NO OD_ID !!!) implemented in hard in the
renderer - for development only.

NoVisualThread (value: yes, no)
specifies whether the visual rendering is done in the main codec manager or in a
dedicated thread.

DefAudioDec, DefVideoDec (value: string)
Specifies which plugin to use by default for audio/video decoding. Example,
"DefVideoDec=name". The name given is the name of the plugin to be used (same
considerations as other plugins, cf above).

codec_XX_XX (value: string)
Allows to specify default media plugin (audio/video) per stream type and object
type. This is usefull if you have more than one decoder for a given type. The
syntax is codec_AA_BB=pluginname where AA is the hexadecimal MPEG-4 streamType
value for the codec (0x04=visual, 0x05=audio) and BB is the hexadecimal MPEG-4
objectTypeIndication of the media (0x20 = MPEG-4 video, 0x40=MPEG-4 Audio, ...).
The name given is the name of the plugin to be used (same considerations as other
plugins, cf above).

SECTION Rendering

The "Rendering" section holds all configuration options for the logical rendering engines,
whether 2D or 3D. The following options are defined:

RendererName (value: string)
specifies which renderer should be used. There are currently 2 renderers available
in GPAC, "GPAC 2D Renderer" and "GPAC 3D Renderer". Renderers cannot be reloaded at
run-time, the complete system must be restarted.

Raster2D (value: string)
specifies the 2D rasterizer to use for vectorial drawing. Used by 2D renderer (for
everything) and 3D renderer (for textured text and gradients).

FrameRate (value: float)
specifies the simulation frame-rate of the presentation - this value is also used
by the MPEG-4 Systems engine to determine when a BIFS frame is mature for decoding.

AntiAlias (value: None, All, Text)
specifies antialiasing settings - whether the setting is applied or not depends on
the graphics plugin/graphic card.
None: no anti-aliasing
Text: anti-aliasing for text only
All: complete anti-aliasing

FastRender (value: yes, no)
specifies whether rendering should target speed or quality - whether the setting is
applied or not depends on the graphics plugin/graphic card.

ForceSceneSize (value: yes, no)
forces the scene to resize to the biggest bitmap available if no size info is given
in the BIFS configuration.

StressMode (value: yes, no)
specifies that the renderer runs in worst case scenario, recomputing all vectorial
paths, meshes, outlines and reloading textures (sending them to graphics card) at
each frame.

BoundingVolume (value: None, Box, AABB)
specifies whether the bounding volume of an object shall be drawn or not. Note that
the 2D renderer only uses rectangles as bounding volumes. The "AABB" value is used
by the 3D renderer only, and specifies the object bounding-box tree shall be drawn.


The "Render2D" section holds all configuration options for the 2D tile rendering engine.
The following options are defined:

DirectRender (value: yes, no)
specifies whether direct rendering should be used or not. In direct rendering mode,
the screen is completely redrawn at each frame. In indirect rendering object
positioning is tracked from frame to frame and dirty rectangles info is collected
in order to redraw the minimal amount of the screen buffer.Whether the setting is
applied or not depends on the graphics plugin (currently all plugins handle both

ScalableZoom (value: yes, no)
specifies whether scalable zoom should be used or not. When scalable zoom is
enabled, resizing the output window will also recompute all vectorial objects.
Otherwise only the final buffer is stretched.


The "Render3D" section holds all configuration options for the 3D openGL rendering engine.
The following options are defined:

RasterOutlines (value: yes, no)
specifies that outlining shall be done through openGL pen width rather than
vectorial outlining.

PolygonAA (value: yes, no)
specifies whether polygon antialiasing should be used in full antialiasing mode. If
not set, only lines and points antialiasing are used.

Wireframe (value: WireNone, WireOnly, WireOnSolid)
specifies wireframe drawing options:
WireNone: objects are drawn as solid
WireOnly: objects are drawn as wireframe only
WireOnSolid: objects are drawn as solid and wireframe is then drawn

DisableRectExt (value: yes, no)
specifies whether openGL rectangular texture extension (GL_EXT_texture_rectangle or
GL_NV_texture_rectangle) shall be used or not.
If "yes", textures whose dimensions are not power of two are rescaled except if
hardware support non-power-of-two textures (GL_ARB_texture_non_power_of_two)
If "no" and extension is available, textures are used without rescaling. Note that
in this case texture transformation are disabled.

EmulatePOW2 (value: yes, no)
enables power of 2 emulation. Ignored if openGL rectangular texture extension is
if set, video texture is not resized but emulated with padding. This usually speeds
up video mapping on shapes but disables texture transformations.
if not set, video is resized to a power of 2 texture when mapping to a shape.

BitmapCopyPixels (value: yes, no)
specifies whether the bitmap node should be drawn with regular openGL texturing
("no") or through pixel copy routines ("yes"). This greatly impacts video rendering
through bitmap depending on the graphics card. Some cards will have faster pixel
copy routines that texture transfer ones, some won't.


The "Audio" section holds all configuration options for the audio rendering engine and
hardware. Note that most options depend on the driver used and may be ignored by the
driver. The following options are defined:

ForceConfig (value: yes, no)
Forces a given sound card configuration to be used. If not set the sound card will
be setup to use 2 audio buffers of 1024 samples each. This may not work properly on
some audio cards due to hardware latency, therefore forcing the config may be very

NumBuffers (value: integer, 0 forbidden)
When config is forced, specifies the number of audio buffers to allocate (audio
buffers are played in ring if possible, otherwise a single audio buffer is

TotalDuration (value: integer, 0 forbidden)
When config is forced, specifies the total audio buffer size in milliseconds. Be
aware that the longer the audio buffer is, the longer the audio latency will be
when pausing an audio object. The quality of fast forward audio playback will also
be degradated when using large audio buffers.
Note: The SDL audio plugin does not use the TotalDuration and num buffers in the
same way, it just computes the desired audio buffer size with this settings and
picks the next power of 2 size for audio buffer size. It does not use ring buffers

NoResync (value: yes, no)
Disables audio resynchronization: audio clock is never adjusted and A/V sync may
get broken

DisableMultiChannel (value: yes, no)
Disables audio multichannel output and always downmix to stereo. This may be
usefull if the multichannel output behaves weirdly.

DisableNotification (value: yes, no)
Disables usage of audio buffer notifications when supported (currently only
DirectSound supports it). If DirectSound audio sounds weird try without
notifications. Ignored on other platforms than Win32/DX.

DriverName (value: string)
specifies the driver to use for audio rendering.

Volume (value: integer, range 0-100)
specifies the default audio volume used when launching GPAC.

Pan (value: integer, range 0-100)
specifies the default audio stereo balance used when launching GPAC - 0 for full
left, 100 for full right, 50 for balanced.


The "Video" section holds all configuration options for the video renderer and hardware.
The following options are defined:

DisableYUV (value: yes, no) - used by 2D renderer only
disables YUV hardware support (YUV hardware support may not be available for the
current plugin).

SwitchResolution (value: yes, no)
if enabled, selects smallest video resolution larger than scene size, otherwise use
current video resolution.

DriverName (value: string)
specifies the driver to use for video memory access.


The "Network" section holds all configuration options for the network used by plugins and
systems engine. The following options are defined:

AutoReconfigUDP (value: yes, no)
specifies if network manager shall reconnect a scene if UDP traffic is blocked.

DataTimeout (value: unsigned int)
specifies timeout in milliseconds befor initial buffering aborts. Default terminal
value is 20000 (20 seconds).

UDPNotAvailable (value: yes, no)
specifies that UDP traffic is not available (usually set by GPAC)

UDPTimeout (value: unsigned int)
specifies timeout in milliseconds for initial UDP detection. Once a UDP packet is
recieved the timeout is ignored.

BufferLength (value: unsigned int)
specifies the default length of the decoding buffer in milliseconds. The client
will wait for the buffer to be filled before starting decoding. A plugin may decide
to use a different value based on protocol and network jitters.

RebufferLength (value: unsigned int)
specifies rebuffering length of the decoding buffer in milliseconds. Whenever the
decoding buffer fullness is less than this value, the object clock is paused and
the stream rebuffered till BufferLength. Therefore a value of 0 means no
rebuffering. A plugin may decide to use a different value based on protocol and
network jitters.

SECTION FontEngine

The "FontEngine" section holds all configuration options for the font handling. The GPAC
rendering module handles text through vectorial outline, allowing graphics plugin
development without having to integrate text rendering which is always heavy work. The
following options are defined:

DriverName (value: string)
specifies the driver to use for font handling.

FontDirectory (value: path)
specifies the directory where fonts are located - currently only one directory can
be specified (however nothing stops a font plugin from using a private directory).
If the directory is invalid or does not contain fonts, text may be unavailable in

TextureTextMode (value: Never, 3D, Always)
specifies whether text shall be drawn to a texture and then rendered or directly
rendered. Using textured text can improve text look in the 3D renderer and also
improve text-on-video like content.

FontSerif (value: string)
specifies default SERIF font.

FontSans (value: string)
specifies default SANS font.

FontFixed (value: string)
specifies default FIXED font.

Note: The freetype plugin uses this section to maintain associations between font names
and truetype font file names. This greatly speeds up font selection at run-time.

SECTION Downloader

The "Downloader" section holds all configuration options for file downloading and caching.

CleanCache (value: yes, no)
specifies whether downloaded files shall be removed once used.

RestartFiles (value: yes, no)
specifies whether incompletely downloaded files shall be removed before

MaxRate (value: positive integer)
specifies a maximum data rate in kilo bits per seconds for file downloading. This
is used for simulation purposes. A value of 0 means no rate restriction.

UserAgent (value: string)
specifies an alternate user agent (default one is "GPAC $VERSION").


The "HTTPProxy" section of the config file holds configuration option for HTTP proxy
adressing. Currently only one proxy can be enabled, and no URI selection is done

Enabled (value: yes, no)
specifies whether the proxy should be used or not when downloading files.

Name (value: string)
specifies the proxy name (IP address or resolved name) without protocol identifier
(eg, no "http://"). If not present, the proxy is disabled.

Port (value: positive integer)
Specifies the port to use with the proxy. If no port is specified, the default HTTP
port (80) is used.

SECTION Streaming

The "Streaming" section holds all configuration options for real-time streaming using IETF
SDP/RTSP/RTP/RTCP protocols.

DefaultPort (value: unsigned short)
specifies the default port to use when connecting to a server (ignored if a port is
specified in the url). If the port is 80 or 8080 (HTTP), the client will connect to
the RTSP server through an HTTP tunnel, and transport will take place on the RTSP

ReorderSize (value: integer)
size of the RTP reordering buffer - 0 means no reordering. Ignored when transport
takes place on the RTSP connection

RTPoverRTSP (value: yes, no)
specifies whether RTP packets should be carried on the RTSP connection (TCP or UDP)
when possible, or carried on UDP. If the connection port is an HTTP port, this
value is assumed to be true

RTSPTimeout (value: unsigned int)
specifies connection timeout with the server: an RTSP request is considered as
failed when the timeout expires.

FirstPacketDrop (value: unsigned int)
specifies the first SL packet to be droped - 0 means no packet drop. Used for
packet drop simulation tests.

PacketDropFrequency (value: unsigned int)
specifies the frequency at which SL packets are droped. If value is 20, one packet
every 20 recieved packets will be droped. Used for packet drop simulation tests.


This section is used to keep MIME types and file associations for GPAC plugins. The format
of the key is: mimeType="fileExt1 filexExt2 .. filexExtN" MimeType description PluginName
The description is used for GUI purposes (open file dialogs). You may modify the file
extension list to support your own extensions. MIME Type is always checked when
processing a remote ressource (eg http file) in order to load the appropriated plugins.
If MIME type is not available, provided extensions are first checked, then all input
plugins are queried.


The "StreamingCache" section of the config file holds all configuration options for the
streaming cache. Streaming cache allows for recording of live sources such as RTP/RTSP
sessions and internet radios. This is currently just an experimental feature in GPAC.
RecordDirectory (value: path) specifies path for recorded files. Cached data is written
directly to disk (no re-interleaving or similar processes). If not specified, the default
cache directory is used.

BaseFileName (value: string)
specifies the base name for recorded files. If not present in configuration file,
the service name (URL) is used.

KeepExistingFiles (value: yes no)
specifies if cached files with same name should be kept or not. If not, an integer
number is added to the cached file name, the higest number for the latest file.

The "SAXLoader" section holds all configuration options for XML SAX parsing of SVG,
XMT and X3D files.

Progressive (value: string)
specifies XML parsing mode used by the loader. Supported modes are:
yes: SAX parsing is used with progressive loading of the document.
no: SAX parsing is used, document will first be completely downloaded.
DOM: DOM parsing is used, document will first be completely downloaded. Only
supported by libXML2 plugin, otherwise handled as "no".

MaxDuration (value positive integer)
specifies the maximum amount of time the SAX parser should spent loading a portion
of the document. Only used in SAX Progressive mode.


The "XviD" section holds all configuration options for the XviD codec.

PostProc (value: string)
specifies filters to apply when decoding video. The string is a list of filters
separated with a space character. Filters supported are:
FilmEffect: xvid 1.0.0 filmEffect.
Deblock_Y: Y plane deblocking filter.
Deblock_UV: UV plane deblocking filter.

Threaded (value yes, no)
specifies whether the decoder should run in its own thread or not.

Section FFMPEG

The "FFMPEG" section holds all configuration options for the FFMPEG demuxer and codec.

DataBufferMS (value: unsigned int)
specifies the amount of video/audio data (in milliseconds) to be bufferer before
starting decoding. For developpers only.

Section ISOReader

The "ISOReader" section holds all configuration options for the ISO Media file demuxer.

IgnoreMPEG-4ForBrands (value: Full 4CC or 4CC pattern (abc* ab*))
ignores all MPEG-4 systems tracks and IOD for files showing the listed brands in
their compatible brand list.


If not found, a default configuration file is created when launching MP4Client or Osmo4.
In this process the font directory and the cache directory must be entered at prompt. The
file is located in the user home directory and called ".gpacrc"

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