【GStreamer开发】GStreamer播放教程03——pipeline的快捷访问

目的

《GStreamer08——pipeline的快捷访问》展示了一个应用如何用appsrc和appsink这两个特殊的element在pipeline中手动输入/提取数据。playbin2也允许使用这两个element，但连接它们的方法有所不同。连接appsink到playbin2的方法在后面还会提到。这里我们主要讲述：

如何把appsrc连接到playbin2

如何配置appsrc

一个playbin2波形发生器

[objc]view plaincopy 
   
 <spanstyle="font-size:14px;">#include<gst/gst.h>
 
  @H_502_65@#include<string.h>
 
  @H_502_65@#defineCHUNK_SIZE1024/*Amountofbyteswearesendingineachbuffer*/#defineSAMPLE_RATE44100/*Samplespersecondwearesending*/
 
  @H_502_65@#defineAUdio_CAPS"audio/x-raw-int,channels=1,rate=%d,signed=(boolean)true,width=16,depth=16,endianness=BYTE_ORDER"/*Structuretocontainallourinformation,sowecanpassittocallbacks*/
typedefstruct_CustomData{
 
  @H_502_65@GstElement*pipeline;GstElement*app_source;
 
  @H_502_65@guint64num_samples;/*Numberofsamplesgeneratedsofar(fortimestampgeneration)*/
 
  @H_502_65@gfloata,b,c,d;/*Forwaveformgeneration*/guintsourceid;/*TocontroltheGSource*/
GMainLoop*main_loop;/*GLib'sMainLoop*/
}CustomData;
 
  @H_502_65@/*ThismethodiscalledbytheidleGSourceinthemainloop,toFeedCHUNK_SIZEbytesintoappsrc. 
  @H_502_65@*Theidehandlerisaddedtothemainloopwhenappsrcrequestsustostartsendingdata(need-datasignal)*andisremovedwhenappsrchasenoughdata(enough-datasignal).
 
  @H_502_65@*/staticgbooleanpush_data(CustomData*data){
 
  @H_502_65@GstBuffer*buffer;GstFlowReturnret;
 
  @H_502_65@inti;gint16*raw;
 
  @H_502_65@gintnum_samples=CHUNK_SIZE/2;/*Becauseeachsampleis16bits*/gfloatfreq;
 
  @H_502_65@/*Createanewemptybuffer*/ 
  @H_502_65@buffer=gst_buffer_new_and_alloc(CHUNK_SIZE);/*Setitstimestampandduration*/
GST_BUFFER_TIMESTAMP(buffer)=gst_util_uint64_scale(data->num_samples,GST_SECOND,SAMPLE_RATE);
 
  @H_502_65@GST_BUFFER_DURATION(buffer)=gst_util_uint64_scale(CHUNK_SIZE,SAMPLE_RATE);/*Generatesomepsychodelicwaveforms*/
raw=(gint16*)GST_BUFFER_DATA(buffer);
 
  @H_502_65@data->c+=data->d;data->d-=data->c/1000;
 
  @H_502_65@freq=1100+11000*data->d;for(i=0;i<num_samples;i++){
 
  @H_502_65@data->a+=data->b;data->b-=data->a/freq;
 
  @H_502_65@raw[i]=(gint16)(5500*data->a);}
 
  @H_502_65@data->num_samples+=num_samples;/*Pushthebufferintotheappsrc*/
g_signal_emit_by_name(data->app_source,"push-buffer",buffer,&ret);
 
  @H_502_65@/*Freethebuffernowthatwearedonewithit*/ 
  @H_502_65@gst_buffer_unref(buffer);if(ret!=GST_FLOW_OK){
/*Wegotsomeerror,stopsendingdata*/
 
  @H_502_65@returnFALSE;returnTRUE;
 
  @H_502_65@}/*Thissignalcallbacktriggerswhenappsrcneedsdata.Here,weaddanidlehandler
*tothemainlooptostartpushingdataintotheappsrc*/
 
  @H_502_65@staticvoidstart_Feed(GstElement*source,guintsize,CustomData*data){if(data->sourceid==0){
 
  @H_502_65@g_print("StartFeeding\n");data->sourceid=g_idle_add((GSourceFunc)push_data,data);
 
  @H_502_65@/*Thiscallbacktriggerswhenappsrchasenoughdataandwecanstopsending. 
  @H_502_65@*Weremovetheidlehandlerfromthemainloop*/staticvoidstop_Feed(GstElement*source,CustomData*data){
 
  @H_502_65@if(data->sourceid!=0){g_print("StopFeeding\n");
 
  @H_502_65@g_source_remove(data->sourceid);data->sourceid=0;
 
  @H_502_65@/*Thisfunctioniscalledwhenanerrormessageispostedonthebus*/ 
  @H_502_65@staticvoiderror_cb(GstBus*bus,GstMessage*msg,0)">GError*err; 
  @H_502_65@gchar*debug_info;/*Printerrordetailsonthescreen*/
gst_message_parse_error(msg,&err,&debug_info);
 
  @H_502_65@g_printerr("Errorreceivedfromelement%s:%s\n",GST_OBJECT_NAME(msg->src),err->message);g_printerr("Debugginginformation:%s\n",debug_info?debug_info:"none");
 
  @H_502_65@g_clear_error(&err);g_free(debug_info);
 
  @H_502_65@g_main_loop_quit(data->main_loop); 
  @H_502_65@/*Thisfunctioniscalledwhenplaybin2hascreatedtheappsrcelement,sowehave*achancetoconfigureit.*/
 
  @H_502_65@staticvoidsource_setup(GstElement*pipeline,GstElement*source,0)">gchar*audio_caps_text; 
  @H_502_65@GstCaps*audio_caps;g_print("Sourcehasbeencreated.Configuring.\n");
data->app_source=source;
 
  @H_502_65@/*Configureappsrc*/ 
  @H_502_65@audio_caps_text=g_strdup_printf(AUdio_CAPS,SAMPLE_RATE);audio_caps=gst_caps_from_string(audio_caps_text);
 
  @H_502_65@g_object_set(source,"caps",audio_caps,NULL);g_signal_connect(source,"need-data",G_CALLBACK(start_Feed),data);
"enough-data",G_CALLBACK(stop_Feed),data);
gst_caps_unref(audio_caps);
 
  @H_502_65@g_free(audio_caps_text);intmain(intargc,charchar*argv[]){
 
  @H_502_65@CustomDatadata;GstBus*bus;
 
  @H_502_65@/*Initializecumstomdatastructure*/ 
  @H_502_65@memset(&data,0,sizeof(data));data.b=1;/*Forwaveformgeneration*/
 
  @H_502_65@data.d=1;/*InitializeGStreamer*/
gst_init(&argc,&argv);
 
  @H_502_65@/*Createtheplaybin2element*/ 
  @H_502_65@data.pipeline=gst_parse_launch("playbin2uri=appsrc://",0)">g_signal_connect(data.pipeline,"source-setup",G_CALLBACK(source_setup),&data); 
  @H_502_65@/*Instructthebustoemitsignalsforeachreceivedmessage,andconnecttotheinterestingsignals*/ 
  @H_502_65@bus=gst_element_get_bus(data.pipeline);gst_bus_add_signal_watch(bus);
 
  @H_502_65@g_signal_connect(G_OBJECT(bus),"message::error",(GCallback)error_cb,&data);gst_object_unref(bus);
 
  @H_502_65@/*Startplayingthepipeline*/ 
  @H_502_65@gst_element_set_state(data.pipeline,GST_STATE_PLAYING);/*CreateaGLibMainLoopandsetittorun*/
data.main_loop=g_main_loop_new(NULL,FALSE);
 
  @H_502_65@g_main_loop_run(data.main_loop);/*Freeresources*/
502_65@gst_object_unref(data.pipeline);
return0;
 
  @H_502_65@</span>

把appsrc用作pipeline的source，仅仅把playbin2的UIR设置成appsrc://即可。

[objc]view plaincopy 
   
<spanstyle="font-size:14px;">/*Createtheplaybin2element*/NULL);</span>

playbin2创建一个内部的appsrc element并且发送source-setup信号来通知应用进行设置。

[objc]view plaincopy 
   
<spanstyle="font-size:14px;">g_signal_connect(data.pipeline,&data);</span>

特别地，设置appsrc的caps属性是很重要的，因为一旦这个信号的处理返回，playbin2就会根据返回值来初始化下一个element。

[objc]view plaincopy 
   
<spanstyle="font-size:14px;">/*Thisfunctioniscalledwhenplaybin2hascreatedtheappsrcelement,sowehave 
  @H_502_65@*achancetoconfigureit.*/gchar*audio_caps_text;
GstCaps*audio_caps;
 
  @H_502_65@g_print("Sourcehasbeencreated.Configuring.\n"); 
  @H_502_65@data->app_source=source;/*Configureappsrc*/
502_65@audio_caps=gst_caps_from_string(audio_caps_text);
NULL);
 
  @H_502_65@gst_caps_unref(audio_caps);g_free(audio_caps_text);
 
  @H_502_65@}</span>

appsrc的配置和《GStreamer08——pipeline的快捷访问》里面一样：caps设置成audio/x-raw-int，注册两个回调，这样element可以在需要/停止给它推送数据时通知应用。具体细节请参考《GStreamer08——pipeline的快捷访问》。

在这个点之后，playbin2接管处理了剩下的pipeline，应用仅仅需要生成数据即可。

至于使用appsink来从从playbin2里面提取数据，在后面的教程里面再讲述。

原文链接：https://www.f2er.com/javaschema/283321.html

【GStreamer开发】GStreamer播放教程03——pipeline的快捷访问

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