Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 92 insertions, 0 deletions

diff --git a/third_party/libwebrtc/docs/native-code/rtp-hdrext/video-layers-allocation00/README.md b/third_party/libwebrtc/docs/native-code/rtp-hdrext/video-layers-allocation00/README.md
new file mode 100644
index 0000000000..cfa8c4cb0d
--- /dev/null
+++ b/third_party/libwebrtc/docs/native-code/rtp-hdrext/video-layers-allocation00/README.md
@@ -0,0 +1,92 @@
+# Video Layers Allocation
+
+The goal of this extension is for a video sender to provide information about
+the target bitrate, resolution and frame rate of each scalability layer in order
+to aid a selective forwarding middlebox to decide which layer to relay.
+
+**Name:** "Video layers allocation version 0"
+
+**Formal name:**
+<http://www.webrtc.org/experiments/rtp-hdrext/video-layers-allocation00>
+
+**Status:** This extension is defined here to allow for experimentation.
+
+In a conference scenario, a video from a single sender may be received by
+several recipients with different downlink bandwidth constraints and UI
+requirements. To allow this, a sender can send video with several scalability
+layers and a middle box can choose a layer to relay for each receiver.
+
+This extension support temporal layers, multiple spatial layers sent on a single
+rtp stream (SVC), or independent spatial layers sent on multiple rtp streams
+(simulcast).
+
+## RTP header extension format
+
+Note: when including the optional width, height and maximum framerate
+fields, the total data length of the extension can exceed 16 bytes
+and is sent as a two-byte header extension [1]
+
+### Data layout
+
+```
+//                           +-+-+-+-+-+-+-+-+
+//                           |RID| NS| sl_bm |
+//                           +-+-+-+-+-+-+-+-+
+// Spatial layer bitmask     |sl0_bm |sl1_bm |
+//   up to 2 bytes           |---------------|
+//   when sl_bm == 0         |sl2_bm |sl3_bm |
+//                           +-+-+-+-+-+-+-+-+
+// Number of temporal layers |#tl|#tl|#tl|#tl|
+// per spatial layer         |   |   |   |   |
+//                           +-+-+-+-+-+-+-+-+
+//  Target bitrate in kpbs   |               |
+//   per temporal layer      :      ...      :
+//    leb128 encoded         |               |
+//                           +-+-+-+-+-+-+-+-+
+// Resolution and framerate  |               |
+// 5 bytes per spatial layer + width-1 for   +
+//      (optional)           | rid=0, sid=0  |
+//                           +---------------+
+//                           |               |
+//                           + height-1 for  +
+//                           | rid=0, sid=0  |
+//                           +---------------+
+//                           | max framerate |
+//                           +-+-+-+-+-+-+-+-+
+//                           :      ...      :
+//                           +-+-+-+-+-+-+-+-+
+```
+
+RID: RTP stream index this allocation is sent on, numbered from 0. 2 bits.
+
+NS: Number of RTP streams minus one. 2 bits, thus allowing up-to 4 RTP streams.
+
+sl_bm: BitMask of the active Spatial Layers when same for all RTP streams or 0
+otherwise. 4 bits, thus allows up to 4 spatial layers per RTP streams.
+
+slX_bm: BitMask of the active Spatial Layers for RTP stream with index=X.
+When NS < 2, takes one byte, otherwise uses two bytes. Zero-padded to byte
+alignment.
+
+\#tl: 2-bit value of number of temporal layers-1, thus allowing up-to 4 temporal
+layers. Values are stored in ascending order of spatial id. Zero-padded to byte
+alignment.
+
+Target bitrate in kbps. Values are stored using leb128 encoding [2]. One value per
+temporal layer. Values are stored in (RTP stream id, spatial id, temporal id)
+ascending order. All bitrates are total required bitrate to receive the
+corresponding layer, i.e. in simulcast mode they include only corresponding
+spatial layers, in full-svc all lower spatial layers are included. All lower
+temporal layers are also included.
+
+Resolution and framerate. Optional. Presence is inferred from the rtp header
+extension size. Encoded (width - 1), 16-bit, (height - 1), 16-bit, max frame
+rate 8-bit per spatial layer per RTP stream. Values are stored in (RTP stream
+id, spatial id) ascending order. Only sent when the resolution differs from the
+last values, the framerate changed by more than 5fps and on key frames.
+
+An empty layer allocation (i.e nothing sent on ssrc) is encoded as
+special case with a single 0 byte.
+
+[1] https://www.rfc-editor.org/rfc/rfc8285#section-4.3
+[2] https://aomediacodec.github.io/av1-spec/#leb128