author | Dremov Kirill (Nokia-D-MSW/Tampere) <kirill.dremov@nokia.com> |
Tue, 31 Aug 2010 15:30:33 +0300 | |
branch | RCL_3 |
changeset 29 | 567bb019e3e3 |
permissions | -rw-r--r-- |
29
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The RTP libraries |
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--------------------- |
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3 |
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RTP Buffers |
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----------- |
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The real time protocol as described in RFC 3550 requires the use of special |
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packets containing an additional RTP header of at least 12 bytes. GStreamer |
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provides some helper functions for creating and parsing these RTP headers. |
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The result is a normal #GstBuffer with an additional RTP header. |
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10 |
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RTP buffers are usually created with gst_rtp_buffer_new_allocate() or |
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gst_rtp_buffer_new_allocate_len(). These functions create buffers with a |
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preallocated space of memory. It will also ensure that enough memory |
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is allocated for the RTP header. The first function is used when the payload |
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size is known. gst_rtp_buffer_new_allocate_len() should be used when the size |
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of the whole RTP buffer (RTP header + payload) is known. |
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When receiving RTP buffers from a network, gst_rtp_buffer_new_take_data() |
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should be used when the user would like to parse that RTP packet. (TODO Ask |
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Wim what the real purpose of this function is as it seems to simply create a |
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duplicate GstBuffer with the same data as the previous one). The |
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function will create a new RTP buffer with the given data as the whole RTP |
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packet. Alternatively, gst_rtp_buffer_new_copy_data() can be used if the user |
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wishes to make a copy of the data before using it in the new RTP buffer. An |
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important function is gst_rtp_buffer_validate() that is used to verify that |
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the buffer a well formed RTP buffer. |
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It is now possible to use all the gst_rtp_buffer_get_*() or |
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gst_rtp_buffer_set_*() functions to read or write the different parts of the |
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RTP header such as the payload type, the sequence number or the RTP |
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timestamp. The use can also retreive a pointer to the actual RTP payload data |
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using the gst_rtp_buffer_get_payload() function. |
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RTP Base Payloader Class (GstBaseRTPPayload) |
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-------------------------------------------- |
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All RTP payloader elements (audio or video) should derive from this class. |
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RTP Base Audio Payloader Class (GstBaseRTPAudioPayload) |
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------------------------------------------------------- |
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This base class can be tested through it's children classes. Here is an |
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example using the iLBC payloader (frame based). |
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567bb019e3e3
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For 20ms mode : |
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GST_DEBUG="basertpaudiopayload:5" gst-launch-0.10 fakesrc sizetype=2 |
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sizemax=114 datarate=1900 ! audio/x-iLBC, mode=20 ! rtpilbcpay |
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max-ptime="40000000" ! fakesink |
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567bb019e3e3
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For 30ms mode : |
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GST_DEBUG="basertpaudiopayload:5" gst-launch-0.10 fakesrc sizetype=2 |
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sizemax=150 datarate=1662 ! audio/x-iLBC, mode=30 ! rtpilbcpay |
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max-ptime="60000000" ! fakesink |
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Here is an example using the uLaw payloader (sample based). |
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GST_DEBUG="basertpaudiopayload:5" gst-launch-0.10 fakesrc sizetype=2 |
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sizemax=150 datarate=8000 ! audio/x-mulaw ! rtppcmupay max-ptime="6000000" ! |
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fakesink |
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RTP Base Depayloader Class (GstBaseRTPDepayload) |
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------------------------------------------------ |
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All RTP depayloader elements (audio or video) should derive from this class. |