Gstreamer Pad

• The relationship between pad and caps

                         |-name_template(eg:wavparse_src, wavparse_sink)
                         |
                         |-direction(src or sink)
    GstStaticPadTemplate-|
            |            |-presence(Sometimes, Always, request)
            |            |
            |            |                  |-GstCaps(String is stored in GstStruct)
            |            |-GstStaticCaps----|
            |                               |-String(support caps)
     gst_static_pad_template_get()
            |
            |           |-GstObject
            V           |
    GstPadTemplate------|-direction
            |           |
            |           |-presence
            |           |
            |           |-GstCaps
            |
     gst_pad_new_from_static_template()
            |
            |
            V    |-GstObject
    GstPad-------|-GstPadTemplate
                 |...
  

• Add pad into element and set relation

  gst_element_add_pad(element, pad)
    {
        _set_parent(element, pad) {
            pad->parent = element
        }
    
        if(pad->direction == src)
            element->srcpads = pad
        else if(pad->direction == sink)
            element->sinkpads = pad
    
        element->pads = pad
    }
    
    +---------+         +------------+         +---------+
    |      parent------>|  element   |<------parent      |
    | Gstpad  |<-----sinkpad      srcpad------>|  GstPad |
    +---------+         +------------+         +---------+
    
  

• Set pad active from srcpad to sinkpad
  1. element state change from READY to PAUSE, set pad active

     gst_element_pads_activate(element, TRUE)
       {
           //set srcpad
           activate_pads(element->srcpads, TRUE);
           //set sinkpad
           activate_pads(element->sinkpads, TRUE);
       }
     

  2. check pad current mode and call pad->activefunc

     gst_pad_set_active(pad)
       {
           mode = GST_PAD_ACTIVATE_MODE(pad);
           if(mode == GST_ACTIVATE_PUSH || mode == GST_ACTIVATE_PULL) {
               //pad already activation
               return TRUE;
           }
           else if (mode == GST_ACTIVATE_NONE)
               GST_PAD_ACTIVATEFUNC(pad) (pad);
       }
     

  3. call pad->activepushfunc or pad->activepullfunc, default is pushfunc

     gst_pad_activate_push(pad)
       {
           GST_PAD_ACTIVATE_MODE(pad) = GST_ACTIVATE_PUSH;
       
           GST_PAD_ACTIVATEPUSHFUNC(pad) (pad);
       }
       gst_pad_activate_pull(pad)
       {
           GST_PAD_ACTIVATE_MODE(pad) = GST_ACTIVATE_PULL;
       
           GST_PAD_ACTIVATEPULLFUNC(pad) (pad);
       }
     

Gstreamer State Change

• Some concepts of States
  1. States defined in gstreamer
     • GST_STATE_VOID_PENDING: the state of an element is not set.
     • GST_STATE_NULL: initial state of an element.
     • GST_STATE_READY: all sources are ready and can go to pause.
     • GST_STATE_PAUSE: ready to accept and process data.
     • GST_STATE_PLAYING: the GstClock is running and the data is flowing.
  2. Variables in GstElement
     • current_state: the current state of an element.
     • next_state: the next state of an element.
     • pending_state: the final state the element should go to.
     • target_state: last state the element we set.
     • last_return: the last return value of an element state change.
  3. The states switch
     
• Create a simple pipe to understand what are states

  $ gst-launch-0.10 alsasrc ! audiorate ! filesink location=test.wav
  

• At the beginning, gstreamer core how to initialize each element
  1. Use funtion gst_element_factory_make("alsasrc", "sound") to create alsasrc element
  2. When create instance of alsasrc(sound), gst_element_init() will initial state of the element.

     GST_STATE_TARGET (element) = GST_STATE_NULL;            //target_state

     GST_STATE_NEXT (element) = GST_STATE_VOID_PENDING;      //next_state

     GST_STATE_PENDING (element) = GST_STATE_VOID_PENDING;   //pending_state

     GST_STATE_RETURN (element) = GST_STATE_CHANGE_SUCCESS;  //last_return 

     GST_STATE (element) = GST_STATE_NULL;                   //current_state 

• Use function gst_bin_add_many to add elements to pipeline. Just add each element to GstBin->children, didn't change state of element
• After link success I want to change state of pipeline from GST_STATE_NULL to GST_STATE_PLAYING
  1. Now the state of element is GST_STATE_NULL, first change the state to GST_STATE_READY. All elements are added in GstBin->cheldren, when we change the state of pipeline to GST_STATE_READY, pipeline will call gst_bin_change_state_func to find child elemnt to change state to GST_STATE_READY. each child element will call plugin->change_state which defined by ourselves.
  2. If state change to GST_STATE_READY successfully, update state of element, then try to change state of pipeline from GST_STATE_READY to GST_STATE_PAUSE. Alsa call gst_bin_change_state_func, the same as step 1.
  3. If state change to GST_STATE_PAUSE successfully, update state of element, then try to change state of pipeline from GST_STATE_PAUSE to GST_STATE_READY. Alsa call gst_bin_change_state_func, the same as step 1.
• When accept message GST_MESSAGE_EOS, try to change the state of pipeline from GST_STATE_PLAYING to GST_STATE_NULL

ubuntu samba server

1. Installl samba

   $ sudo apt-get install samba4 

   (install samba, server can not start, i don't know why)

   $ sudo apt-get install smbclient
   

2. Configure /etc/samba/smb.conf

   [global]
         security = share

   [share]
         comment = chenorui
         path = /home/chenorui/share
         public = yes
         guest ok = yes
         browsable = yes
         writable = no
   

3. Restart samba server

   $ sudo /etc/init.d/samba4 restart
   

4. Look at what services are available on a server

   $ smbclient -L //yourIP
     Domain=[WORKGROUP] OS=[Unix] Server=[Samba 3.5.4]
     
     Sharename       Type      Comment
     ---------       ----      -------
     IPC$            IPC       IPC Service (chenorui server (Samba, Ubuntu))
     share           Disk      chenorui
     HP-LaserJet-M1522 Printer   HP LaserJet M1522
     Domain=[WORKGROUP] OS=[Unix] Server=[Samba 3.5.4]
     
     Server               Comment
     ---------            -------
     
     Workgroup            Master
     ---------            -------
   

5. Login share profile

   $ smbclient //yourIP/share
     smb: \>
   

6. mount share profile

   $ sudo smbmount //yourIP/share /tmp/test
   

gstreamer caps negotiation

协商过程中主要函数:
gst_pad_get_caps/gst_pad_set_getcaps_function, gst_pad_set_caps/gst_pad_set_setcaps_function。

gst_pad_get_caps 函数用来返回该pad能接受的caps。首先检查getcaps函数指针是否为NULL，如果不是则调用getcaps函数，这是一个函数指针，我们可以通过gst_pad_set_getcaps_function来给这个函数指针赋值，从而实现自定义的get_caps函数的逻辑。完成后函数返回；如果getcaps函数指针为NULL，则gst_pad_get_caps函数从该pad的pad template中列出所有的caps，返回；如果该pad没有pad template，则gst_pad_get_caps函数检查该GstPad的caps成员是否为NULL，如果不为NULL，则返回这个 member；最后，如果前面的都不成立，则gst_pad_get_caps创建一个empty的GstCaps并返回，表示该pad目前没有caps。

get_pad_set_caps 函数用来设置指定pad的caps。该函数首先检查参数中给出的caps是否已经和目前该pad中的caps相同，如果是，则直接返回。如果不相同，则检查setcaps函数指针是否为NULL，如果不为NULL则调用setcaps函数。我们可以通过 gst_pad_set_setcaps_function函数来给setcaps这个函数指针赋值，这样就在gst_pad_set_caps函数中实现了自定义的逻辑。注意，gst_pad_set_caps函数会判断setcaps函数的返回值，如果是FALSE，则会直接报错return FALSE，这样的结果就是gst_pad_set_caps函数执行失败，caps negotiation失败。当setcaps函数执行完毕后，gst_pad_set_caps函数执行gst_caps_replace，将保存在该pad中的caps member替换成参数中指定的caps，然后函数结束。

PUSH MODE:   

              src              sink
              |                 |
              |  accepts?       |
  type A      |---------------->|
              |      yes        |
              |<----------------|
              |                 |
 get buffer   |  alloc_buf      |
 from pool    |---------------->| 
 with type A  |                 | Create buffer of type A.
              |                 |
 check type   |<----------------|
 and use A    |                 |
              |  push           |
 push buffer  |---------------->| Receive type A, reconfigure to
 with new type|                 | process type A.
              |                 |

PUSH MODE下，总是由src pad发起negotiation，为了让src pad和peer sink pad都能接受的caps来，src pad会将自己的caps和peer sink pad的caps做intersect，这时就会调用函数gst_pad_get_caps，参数就是peer sink pad（一般直接使用gst_pad_peer_get_caps函数一步完成）。如果 peer sink pad没有设置getcaps函数指针的话，那就会直接返回peer sink pad template中的所有caps。接下去就是src pad调用gst_pad_set_caps，把自己的caps确定下来，再然后就是申请并分配buffer

PULL MODE

src              sink
              |                 |
              |  accepts?       |
              |<----------------| type B
              |      yes        |
              |---------------->|
              |                 |
 get buffer   |  alloc_buf      |
 from pool    |---------------->| 
 with type A  |                 | Create buffer of new type B.
              |                 |
 check type   |<----------------|
 and          |                 |
 reconfigure  |                 |
              | pull            |

              |<----------------| Pull buffer from the peer src pad 

              |                 |

PULL MODE下，由于是sink element的sink pad来drive pipeline，所以，caps negotiation要在pull thread启动之前就完成。首先，sink pad将自己的caps和peer src pad的caps做intersect（需调用peer src pad上的gst_pad_get_caps），之后调用gst_pad_set_caps将sink pad caps确定下来。调用gst_pad_set_caps，设置peer src pad，如果成功，那么表示src pad和自己一样，都具备了相同的caps，这样negotiation就成功了。最后，可以使用gst_pad_pull_range来获取数据，这个函数会为我们检查buffer中的caps和当前sink pad中的caps是否一致，如果不一致，就会return GST_FLOW_NOT_NEGOTIATED。

gst_pad_set_caps 被调用的时机。当在_chain函数中收到一个buffer之后，一般需要检查该buffer中的caps是否和当前pad中的caps相同，以防止数据在运行过程中改变caps。如果这两个caps不相同，那么，_chain函数应该返回GST_FLOW_NOT_NEGOTIATED，这样，gstreamer core就会用buffer中这个新的caps，去调用gst_pad_set_caps，这样做的目的是gstreamer要知道pad能否接受这个 caps，如果函数返回TRUE，表示接受该caps，而且pad已经更新了自己的caps为目前这个，如果函数返回FALSE，表示caps negotiation failed，pipeline就无法正常运行了。

在 PUSH模式下，_chain函数返回GST_FLOW_NOT_NEGOTIATED，gstreamer core就会自动为我们调用gst_pad_set_caps；但是在PULL模式下，虽然gst_pad_pull_range也会返回 GST_FLOW_NOT_NEGOTIATED，但是gst_pad_set_caps并不会自动被调用，gstramer不支持在pull thread中做set caps的动作。所以，在PULL模式下，我们需要自己处理这种GST_FLOW_NOT_NEGOTIATED的情况。回想pull thread没有启动之前，为什么我们需要设置setcaps函数呢？这是因为我们需要在这个函数中，使用gst_pad_set_caps来给peer src pad设置caps来完成caps negotiation，而这个动作在PUSH模式下，只要peer element的_chain函数返回GST_FLOW_NOT_NEGOTIATED，gstreamer core就会自动为我们调用peer src pad上的gst_pad_set_caps，所以，PUSH模式下，我们不需要去设置setcaps函数指针。

不能上网了！！！！

adsl modern坏了，上不了网，狂晕:(
周末逛电脑城。。。