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Diffstat (limited to 'third_party/libwebrtc/docs/native-code/rtp-hdrext/video-timing/README.md')
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diff --git a/third_party/libwebrtc/docs/native-code/rtp-hdrext/video-timing/README.md b/third_party/libwebrtc/docs/native-code/rtp-hdrext/video-timing/README.md new file mode 100644 index 0000000000..6f862f6157 --- /dev/null +++ b/third_party/libwebrtc/docs/native-code/rtp-hdrext/video-timing/README.md @@ -0,0 +1,42 @@ +# Video Timing + +The Video Timing extension is used to communicate a timing information on +per-frame basis to receiver of rtp video stream. Contact <ilnik@google.com> for +more info. It may be generalized to audio frames as well in the future. + +Name: "Video Timing" ; "RTP Header Extension for Video timing" + +Formal name: <http://www.webrtc.org/experiments/rtp-hdrext/video-timing> + +SDP "a= name": "video-timing" ; this is also used in client/cloud signaling. + +Wire format: 1-byte extension, 13 bytes of data. Total 14 bytes extra per packet +(plus 1-3 padding byte in some cases, plus shared 4 bytes for all extensions +present: 2 byte magic word 0xBEDE, 2 byte # of extensions). + +First byte is a flags field. Defined flags: + + * 0x01 - extension is set due to timer. + * 0x02 - extension is set because the frame is larger than usual. + +Both flags may be set at the same time. All remaining 6 bits are reserved and +should be ignored. + +Next, 6 timestamps are stored as 16-bit values in big-endian order, representing +delta from the capture time of a packet in ms. +Timestamps are, in order: + + * Encode start. + * Encode finish. + * Packetization complete. + * Last packet left the pacer. + * Reserved for network. + * Reserved for network (2). + +Pacer timestamp should be updated inside the RTP packet by pacer component when +the last packet (containing the extension) is sent to the network. Last two, +reserved timstamps, are not set by the sender but are reserved in packet for any +in-network RTP stream processor to modify. + +Notes: Extension shoud be present only in the last packet of video frames. If +attached to other packets it should be ignored. |