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43 lines
1.6 KiB
43 lines
1.6 KiB
7 months ago
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# Video Timing
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The Video Timing extension is used to communicate a timing information on
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per-frame basis to receiver of rtp video stream. Contact <ilnik@google.com> for
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more info. It may be generalized to audio frames as well in the future.
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Name: "Video Timing" ; "RTP Header Extension for Video timing"
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Formal name: <http://www.webrtc.org/experiments/rtp-hdrext/video-timing>
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SDP "a= name": "video-timing" ; this is also used in client/cloud signaling.
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Wire format: 1-byte extension, 13 bytes of data. Total 14 bytes extra per packet
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(plus 1-3 padding byte in some cases, plus shared 4 bytes for all extensions
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present: 2 byte magic word 0xBEDE, 2 byte # of extensions).
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First byte is a flags field. Defined flags:
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* 0x01 - extension is set due to timer.
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* 0x02 - extension is set because the frame is larger than usual.
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Both flags may be set at the same time. All remaining 6 bits are reserved and
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should be ignored.
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Next, 6 timestamps are stored as 16-bit values in big-endian order, representing
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delta from the capture time of a packet in ms.
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Timestamps are, in order:
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* Encode start.
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* Encode finish.
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* Packetization complete.
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* Last packet left the pacer.
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* Reserved for network.
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* Reserved for network (2).
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Pacer timestamp should be updated inside the RTP packet by pacer component when
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the last packet (containing the extension) is sent to the network. Last two,
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reserved timstamps, are not set by the sender but are reserved in packet for any
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in-network RTP stream processor to modify.
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Notes: Extension shoud be present only in the last packet of video frames. If
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attached to other packets it should be ignored.
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