rtc_rtcp/payload_feedbacks/receiver_estimated_maximum_bitrate/
mod.rs

1#[cfg(test)]
2mod receiver_estimated_maximum_bitrate_test;
3
4use crate::{header::*, packet::*, util::*};
5use shared::{
6    error::{Error, Result},
7    marshal::{Marshal, MarshalSize, Unmarshal},
8};
9
10use bytes::{Buf, BufMut};
11use std::any::Any;
12use std::fmt;
13
14/// ReceiverEstimatedMaximumBitrate contains the receiver's estimated maximum bitrate.
15///
16/// ## Specifications
17///
18/// * [draft-alvestrand-rmcat-remb-03]
19///
20/// [draft-alvestrand-rmcat-remb-03]: https://tools.ietf.org/html/draft-alvestrand-rmcat-remb-03
21#[derive(Debug, PartialEq, Default, Clone)]
22pub struct ReceiverEstimatedMaximumBitrate {
23    /// SSRC of sender
24    pub sender_ssrc: u32,
25
26    /// Estimated maximum bitrate
27    pub bitrate: f32,
28
29    /// SSRC entries which this packet applies to
30    pub ssrcs: Vec<u32>,
31}
32
33const REMB_OFFSET: usize = 16;
34
35/// Keep a table of powers to units for fast conversion.
36const BIT_UNITS: [&str; 7] = ["b", "Kb", "Mb", "Gb", "Tb", "Pb", "Eb"];
37const UNIQUE_IDENTIFIER: [u8; 4] = [b'R', b'E', b'M', b'B'];
38
39/// String prints the REMB packet in a human-readable format.
40impl fmt::Display for ReceiverEstimatedMaximumBitrate {
41    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
42        // Do some unit conversions because b/s is far too difficult to read.
43        let mut bitrate = self.bitrate;
44        let mut powers = 0;
45
46        // Keep dividing the bitrate until it's under 1000
47        while bitrate >= 1000.0 && powers < BIT_UNITS.len() {
48            bitrate /= 1000.0;
49            powers += 1;
50        }
51
52        let unit = BIT_UNITS[powers];
53
54        write!(
55            f,
56            "ReceiverEstimatedMaximumBitrate {:x} {:.2} {}/s",
57            self.sender_ssrc, bitrate, unit,
58        )
59    }
60}
61
62impl Packet for ReceiverEstimatedMaximumBitrate {
63    /// Header returns the Header associated with this packet.
64    fn header(&self) -> Header {
65        Header {
66            padding: get_padding_size(self.raw_size()) != 0,
67            count: FORMAT_REMB,
68            packet_type: PacketType::PayloadSpecificFeedback,
69            length: ((self.marshal_size() / 4) - 1) as u16,
70        }
71    }
72
73    /// destination_ssrc returns an array of SSRC values that this packet refers to.
74    fn destination_ssrc(&self) -> Vec<u32> {
75        self.ssrcs.clone()
76    }
77
78    fn raw_size(&self) -> usize {
79        HEADER_LENGTH + REMB_OFFSET + self.ssrcs.len() * 4
80    }
81
82    fn as_any(&self) -> &dyn Any {
83        self
84    }
85
86    fn equal(&self, other: &dyn Packet) -> bool {
87        other
88            .as_any()
89            .downcast_ref::<ReceiverEstimatedMaximumBitrate>()
90            == Some(self)
91    }
92
93    fn cloned(&self) -> Box<dyn Packet> {
94        Box::new(self.clone())
95    }
96}
97
98impl MarshalSize for ReceiverEstimatedMaximumBitrate {
99    fn marshal_size(&self) -> usize {
100        let l = self.raw_size();
101        // align to 32-bit boundary
102        l + get_padding_size(l)
103    }
104}
105
106impl Marshal for ReceiverEstimatedMaximumBitrate {
107    /// Marshal serializes the packet and returns a byte slice.
108    fn marshal_to(&self, mut buf: &mut [u8]) -> Result<usize> {
109        const BITRATE_MAX: f32 = 2.417_842_4e24; //0x3FFFFp+63;
110
111        /*
112            0                   1                   2                   3
113            0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
114           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
115           |V=2|P| FMT=15  |   PT=206      |             length            |
116           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
117           |                  SSRC of packet sender                        |
118           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
119           |                  SSRC of media source                         |
120           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
121           |  Unique identifier 'R' 'E' 'M' 'B'                            |
122           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
123           |  Num SSRC     | BR Exp    |  BR Mantissa                      |
124           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
125           |   SSRC feedback                                               |
126           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
127           |  ...                                                          |
128        */
129
130        if buf.remaining_mut() < self.marshal_size() {
131            return Err(Error::BufferTooShort);
132        }
133
134        let h = self.header();
135        let n = h.marshal_to(buf)?;
136        buf = &mut buf[n..];
137
138        buf.put_u32(self.sender_ssrc);
139        buf.put_u32(0); // always zero
140
141        buf.put_slice(&UNIQUE_IDENTIFIER);
142
143        // Write the length of the ssrcs to follow at the end
144        buf.put_u8(self.ssrcs.len() as u8);
145
146        let mut exp = 0;
147        let mut bitrate = self.bitrate;
148        if bitrate >= BITRATE_MAX {
149            bitrate = BITRATE_MAX
150        }
151
152        if bitrate < 0.0 {
153            return Err(Error::InvalidBitrate);
154        }
155
156        while bitrate >= (1 << 18) as f32 {
157            bitrate /= 2.0;
158            exp += 1;
159        }
160
161        if exp >= (1 << 6) {
162            return Err(Error::InvalidBitrate);
163        }
164
165        let mantissa = bitrate.floor() as u32;
166
167        // We can't quite use the binary package because
168        // a) it's a uint24 and b) the exponent is only 6-bits
169        // Just trust me; this is big-endian encoding.
170        buf.put_u8((exp << 2) as u8 | (mantissa >> 16) as u8);
171        buf.put_u8((mantissa >> 8) as u8);
172        buf.put_u8(mantissa as u8);
173
174        // Write the SSRCs at the very end.
175        for ssrc in &self.ssrcs {
176            buf.put_u32(*ssrc);
177        }
178
179        if h.padding {
180            put_padding(buf, self.raw_size());
181        }
182
183        Ok(self.marshal_size())
184    }
185}
186
187impl Unmarshal for ReceiverEstimatedMaximumBitrate {
188    /// Unmarshal reads a REMB packet from the given byte slice.
189    fn unmarshal<B>(raw_packet: &mut B) -> Result<Self>
190    where
191        Self: Sized,
192        B: Buf,
193    {
194        let raw_packet_len = raw_packet.remaining();
195        // 20 bytes is the size of the packet with no SSRCs
196        if raw_packet_len < 20 {
197            return Err(Error::PacketTooShort);
198        }
199
200        const MANTISSA_MAX: u32 = 0x7FFFFF;
201        /*
202            0                   1                   2                   3
203            0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
204           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
205           |V=2|P| FMT=15  |   PT=206      |             length            |
206           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
207           |                  SSRC of packet sender                        |
208           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
209           |                  SSRC of media source                         |
210           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
211           |  Unique identifier 'R' 'E' 'M' 'B'                            |
212           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
213           |  Num SSRC     | BR Exp    |  BR Mantissa                      |
214           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
215           |   SSRC feedback                                               |
216           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
217           |  ...                                                          |
218        */
219        let header = Header::unmarshal(raw_packet)?;
220
221        if header.packet_type != PacketType::PayloadSpecificFeedback || header.count != FORMAT_REMB
222        {
223            return Err(Error::WrongType);
224        }
225
226        let sender_ssrc = raw_packet.get_u32();
227        let media_ssrc = raw_packet.get_u32();
228        if media_ssrc != 0 {
229            return Err(Error::SsrcMustBeZero);
230        }
231
232        // REMB rules all around me
233        let mut unique_identifier = [0; 4];
234        unique_identifier[0] = raw_packet.get_u8();
235        unique_identifier[1] = raw_packet.get_u8();
236        unique_identifier[2] = raw_packet.get_u8();
237        unique_identifier[3] = raw_packet.get_u8();
238        if unique_identifier[0] != UNIQUE_IDENTIFIER[0]
239            || unique_identifier[1] != UNIQUE_IDENTIFIER[1]
240            || unique_identifier[2] != UNIQUE_IDENTIFIER[2]
241            || unique_identifier[3] != UNIQUE_IDENTIFIER[3]
242        {
243            return Err(Error::MissingRembIdentifier);
244        }
245
246        // The next byte is the number of SSRC entries at the end.
247        let ssrcs_len = raw_packet.get_u8() as usize;
248
249        // Get the 6-bit exponent value.
250        let b17 = raw_packet.get_u8();
251        let mut exp = (b17 as u64) >> 2;
252        exp += 127; // bias for IEEE754
253        exp += 23; // IEEE754 biases the decimal to the left, abs-send-time biases it to the right
254
255        // The remaining 2-bits plus the next 16-bits are the mantissa.
256        let b18 = raw_packet.get_u8();
257        let b19 = raw_packet.get_u8();
258        let mut mantissa = ((b17 & 3) as u32) << 16 | (b18 as u32) << 8 | b19 as u32;
259
260        if mantissa != 0 {
261            // ieee754 requires an implicit leading bit
262            while (mantissa & (MANTISSA_MAX + 1)) == 0 {
263                exp -= 1;
264                mantissa *= 2;
265            }
266        }
267
268        // bitrate = mantissa * 2^exp
269        let bitrate = f32::from_bits(((exp as u32) << 23) | (mantissa & MANTISSA_MAX));
270
271        let mut ssrcs = vec![];
272        for _i in 0..ssrcs_len {
273            ssrcs.push(raw_packet.get_u32());
274        }
275
276        if
277        /*header.padding &&*/
278        raw_packet.has_remaining() {
279            raw_packet.advance(raw_packet.remaining());
280        }
281
282        Ok(ReceiverEstimatedMaximumBitrate {
283            sender_ssrc,
284            //media_ssrc,
285            bitrate,
286            ssrcs,
287        })
288    }
289}
rtc_rtcp/payload_feedbacks/receiver_estimated_maximum_bitrate/mod.rs

rtc_rtcp/payload_feedbacks/receiver_estimated_maximum_bitrate/
mod.rs
