gstfilesrc源文件.docx
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gstfilesrc源文件
/*GStreamer
*Copyright（C）1999,2000ErikWalthinsen
*2000,2005WimTaymans
*
*gstfilesrc.c:
*
*Thislibraryisfreesoftware;youcanredistributeitand/or
*modifyitunderthetermsoftheGNULibraryGeneralPublic
*LicenseaspublishedbytheFreeSoftwareFoundation;either
*version2oftheLicense,or（atyouroption）anylaterversion.
*
*Thislibraryisdistributedinthehopethatitwillbeuseful,
*butWITHOUTANYWARRANTY;withouteventheimpliedwarrantyof
*MERCHANTABILITYorFITNESSFORAPARTICULARPURPOSE.SeetheGNU
*LibraryGeneralPublicLicenseformoredetails.
*
*YoushouldhavereceivedacopyoftheGNULibraryGeneralPublic
*Licensealongwiththislibrary;ifnot,writetothe
*FreeSoftwareFoundation,Inc.,59TemplePlace-Suite330,
*Boston,MA02111-1307,USA.
*/
/**
*SECTION:
element-filesrc
*@see_also:
#GstFileSrc
*
*Readdatafromafileinthelocalfilesystem.
*/
#ifdefHAVE_CONFIG_H
#include"config.h"
#endif
#include
#include"gstfilesrc.h"
#include
#include
#ifdefG_OS_WIN32
#include/*lseek,open,close,read*/
/*Onwin32,stat*defaultto32bit;weneedthe64-bit
*variants,soexplicitlydefineitthatway.*/
#definestat__stat64
#definefstat_fstat64
#undeflseek
#definelseek_lseeki64
#undefoff_t
#defineoff_tguint64
/*Preventstat.hfromdefiningthestat*functionsas
*_stat*,sincewe'reexplicitlyoverridingthat*/
#undef_INC_STAT_INL
#endif
#include
#include
#ifdefHAVE_UNISTD_H
#include
#endif
#ifdefHAVE_MMAP
#include
#endif
#include
#include
#include"../../gst/gst-i18n-lib.h"
staticGstStaticPadTemplatesrctemplate=GST_STATIC_PAD_TEMPLATE（"src",
GST_PAD_SRC,
GST_PAD_ALWAYS,
GST_STATIC_CAPS_ANY）;
/*FIXMEweshouldbeusingglibforthis*/
#ifndefS_ISREG
#defineS_ISREG（mode）（（mode）&_S_IFREG）
#endif
#ifndefS_ISDIR
#defineS_ISDIR（mode）（（mode）&_S_IFDIR）
#endif
#ifndefS_ISSOCK
#defineS_ISSOCK（x）（0）
#endif
#ifndefO_BINARY
#defineO_BINARY（0）
#endif
/*Copyofglib'sg_openduetowin32libc/cross-DLLbrokenness:
wecan't
*usethe'filedescriptor'openedinglib（andreturnedfromthisfunction）
*inthislibrary,astheymayhaveunrelatedCruntimes.*/
int
gst_open（constgchar*filename,intflags,intmode）
{
#ifdefG_OS_WIN32
wchar_t*wfilename=g_utf8_to_utf16（filename,-1,NULL,NULL,NULL）;
intretval;
intsave_errno;
if（wfilename==NULL）{
errno=EINVAL;
return-1;
}
retval=_wopen（wfilename,flags,mode）;
save_errno=errno;
g_free（wfilename）;
errno=save_errno;
returnretval;
#else
returnopen（filename,flags,mode）;
#endif
}
/**********************************************************************
*GStreamerDefaultFileSource
*TheoryofOperation
*
*Update:
seeGstFileSrc:
use-mmappropertydocumentationbelow
*forwhyuseofmmap（）isdisabledbydefault.
*
*Thissourceusesmmap
（2）toefficientlyloaddatafromafile.
*Todothiswithoutseriouslypollutingtheapplications'memory
*space,itmustdosoinsmallerchunks,say1-4MBatatime.
*Buffersarethensubdividedfromthesemmap'dchunks,todirectly
*makeuseofthemmap.
*
*Tohandlerefcountingsothatthemmapcanbefreedattheappropriate
*time,abufferwillbecreatedforeachmmap'dregion,andallnew
*bufferswillbesub-buffersofthistop-levelbuffer.Astheyare
*freed,therefcountgoesdownonthemmap'dbufferanditsfree（）
*functioniscalled,whichwillcallmunmap
（2）onitself.
*
*Ifabufferhappenstocrosstheboundariesofanmmap'dregion,we
*havetodecidewhetherit'smoreefficienttocopythedataintoa
*newbuffer,ormmap（）justthatbuffer.Therewillhavetobea
*breakpointsizetodeterminewhichwillbedone.Themmap（）size
*hasalottodowiththisaswell,becauseyouendupindouble-
*jeopardy:
thelargertheoutgoingbuffer,themoredatatocopywhen
*itoverlaps,*and*themorefrequentlyyou'llhavebuffersthat*do*
*overlap.
*
*Seekingisanothertrickyaspecttodoefficiently.Theinitial
*implementationofthissourcewon'tmakeuseofthesefeatures,however.
*Theissueisthatifanapplicationseeksbackwardsinafile,*and*
*thatregionofthefileiscoveredbyanmmapthathasn'tbeenfully
*deallocated,wereallyshouldre-useit.Butkeepingtrackofthese
*regionsistrickybecausewehavetolockthestructurethatholds
*them.Weneedtosettleonalockingprimitive（GMutexseemstobe
*areallygoodoption...）,thenwecandothat.
*/
GST_DEBUG_CATEGORY_STATIC（gst_file_src_debug）;
#defineGST_CAT_DEFAULTgst_file_src_debug
/*FileSrcsignalsandargs*/
enum
{
/*FILLME*/
LAST_SIGNAL
};
#defineDEFAULT_BLOCKSIZE4*1024
#defineDEFAULT_MMAPSIZE4*1024*1024
#defineDEFAULT_TOUCHTRUE
#defineDEFAULT_USEMMAPFALSE
#defineDEFAULT_SEQUENTIALFALSE
enum
{
ARG_0,
ARG_LOCATION,
ARG_FD,
ARG_MMAPSIZE,
ARG_SEQUENTIAL,
ARG_TOUCH,
ARG_USEMMAP
};
staticvoidgst_file_src_finalize（GObject*object）;
//设置属性的虚函数
staticvoidgst_file_src_set_property（GObject*object,guintprop_id,
constGValue*value,GParamSpec*pspec）;
//获取属性的虚函数
staticvoidgst_file_src_get_property（GObject*object,guintprop_id,
GValue*value,GParamSpec*pspec）;
staticgbooleangst_file_src_start（GstBaseSrc*basesrc）;
staticgbooleangst_file_src_stop（GstBaseSrc*basesrc）;
staticgbooleangst_file_src_is_seekable（GstBaseSrc*src）;
staticgbooleangst_file_src_get_size（GstBaseSrc*src,guint64*size）;
staticGstFlowReturngst_file_src_create（GstBaseSrc*src,guint64offset,
guintlength,GstBuffer**buffer）;
staticgbooleangst_file_src_query（GstBaseSrc*src,GstQuery*query）;
staticvoidgst_file_src_uri_handler_init（gpointerg_iface,
gpointeriface_data）;
staticvoid
_do_init（GTypefilesrc_type）
{
staticconstGInterfaceInfourihandler_info={
gst_file_src_uri_handler_init,
NULL,
NULL
};
g_type_add_interface_static（filesrc_type,GST_TYPE_URI_HANDLER,
&urihandler_info）;
GST_DEBUG_CATEGORY_INIT（gst_file_src_debug,"filesrc",0,"filesrcelement"）;
}
GST_BOILERPLATE_FULL（GstFileSrc,gst_file_src,GstBaseSrc,GST_TYPE_BASE_SRC,
_do_init）;
//初始化类结构，定义父类，定义类成员（子类），类详细信息。
//元件细节在_base_init（）函数中被注册到插件中
//：
_base_init（）用来在创建每个新的子类时，初始化类和子类的属性
staticvoid
gst_file_src_base_init（gpointerg_class）
{
GstElementClass*gstelement_class=GST_ELEMENT_CLASS（g_class）;
gst_element_class_set_details_simple（gstelement_class,
"FileSource",
"Source/File",
"Readfromarbitrarypointinafile",
"ErikWalthinsen"）;
//将pad模板注册到element中
gst_element_class_add_pad_template（gstelement_class,
gst_static_pad_template_get（&srctemplate））;
}
//定义类成员变量：
1、定义信号及其响应函数；2、定义虚函数等等。
//_class_init（）用来对类进行初始化（指定类的信号，参数和虚函数，设定全局状态），该初始化过程只进行一次
staticvoid
gst_file_src_class_init（GstFileSrcClass*klass）
{
GObjectClass*gobject_class;
GstBaseSrcClass*gstbasesrc_class;
gobject_class=G_OBJECT_CLASS（klass）;
gstbasesrc_class=GST_BASE_SRC_CLASS（klass）;
gobject_class->set_property=gst_file_src_set_property;
gobject_class->get_property=gst_file_src_get_property;
g_object_class_install_property（gobject_class,ARG_FD,
g_param_spec_int（"fd","File-descriptor",
"File-descriptorforthefilebeingmmap（）d",0,G_MAXINT,0,
G_PARAM_READABLE|G_PARAM_STATIC_STRINGS））;
g_object_class_install_property（gobject_class,ARG_LOCATION,
g_param_spec_string（"location","FileLocation",
"Locationofthefiletoread",NULL,
G_PARAM_READWRITE|G_PARAM_STATIC_STRINGS|
GST_PARAM_MUTABLE_READY））;
g_object_class_install_property（gobject_class,ARG_MMAPSIZE,
g_param_spec_ulong（"mmapsize","mmap（）BlockSize",
"Sizeinbytesofmmap（）dregions",0,G_MAXULONG,DEFAULT_MMAPSIZE,
G_PARAM_READWRITE|G_PARAM_STATIC_STRINGS|
GST_PARAM_MUTABLE_PLAYING））;
g_object_class_install_property（gobject_class,ARG_TOUCH,
g_param_spec_boolean（"touch","Touchmappedregionreaddata",
"Touchmmappeddataregionstoforcethemtobereadfromdisk",
DEFAULT_TOUCH,
G_PARAM_READWRITE|G_PARAM_STATIC_STRINGS|
GST_PARAM_MUTABLE_PLAYING））;
/**
*GstFileSrc:
use-mmap
*
*Whethertousemmap（）.SettoTRUEtoforceuseofmmap（）insteadof
*read（）forreadingdata.
*
*Useofmmap（）isdisabledbydefaultsincewithmmap（）therearea
*numberofoccasionswheretheprocess/applicationwillbenotifiedof
*readerrorsviaaSIGBUSsignalfromthekernel,whichwillleadto
*theapplicationbeingkilledifnothandledbytheapplication.This
*issomethingthatisdifficulttoworkaroundforalibrarylike
*GStreamer,henceuseofmmap（）isdisabledbydefault.Saiderrors
*canoccurforexamplewhenanexternaldevice（e.g.anexternalhard
*driveoraportablemusicplayer）areunpluggedwhileinuse,orwhen
*aCD/DVDmediumcannotbebereadbecausethemediumisscratchedor
*otherwisedamaged.
*
**/
g_object_class_install_property（gobject_class,ARG_USEMMAP,
g_param_spec_boolean（"use-mmap","Usemmaptoreaddata",
"Whethertousemmap（）insteadofread（）",
DEFAULT_USEMMAP,G_PARAM_READWRITE|G_PARAM_STATIC_STRINGS|
GST_PARAM_MUTABLE_READY））;
g_object_class_install_property（gobject_class,ARG_SEQUENTIAL,
g_param_spec_boolean（"sequential","Optimiseforsequentialmmapaccess",
"Whethertousemadvisetohinttothekernelthataccessto"
"mmappageswillbesequential",
DEFAULT_SEQUENTIAL,G_PARAM_READWRITE|G_PARAM_STATIC_STRINGS|
GST_PARAM_MUTABLE_PLAYING））;
gobj
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