blob: ebf109eecb283ccefd04746d24a16ed81a467ab8 [file] [log] [blame]
/*
* Copyright (c) 2019 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "modules/rtp_rtcp/source/rtp_packetizer_av1.h"
#include <stddef.h>
#include <stdint.h>
#include <algorithm>
#include "api/array_view.h"
#include "api/video/video_frame_type.h"
#include "modules/rtp_rtcp/source/leb128.h"
#include "modules/rtp_rtcp/source/rtp_packet_to_send.h"
#include "rtc_base/byte_buffer.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"
namespace webrtc {
namespace {
constexpr int kAggregationHeaderSize = 1;
// when there are 3 or less OBU (fragments) in a packet, size of the last one
// can be omited.
constexpr int kMaxNumObusToOmitSize = 3;
constexpr uint8_t kObuSizePresentBit = 0b0'0000'010;
constexpr int kObuTypeSequenceHeader = 1;
constexpr int kObuTypeTemporalDelimiter = 2;
constexpr int kObuTypeTileList = 8;
constexpr int kObuTypePadding = 15;
// Overhead introduced by "even distribution" of packet sizes.
constexpr size_t kBytesOverheadEvenDistribution = 1;
// Experimentally determined minimum amount of potential savings per packet to
// make "even distribution" of packet sizes worthwhile.
constexpr size_t kMinBytesSavedPerPacketWithEvenDistribution = 10;
bool ObuHasExtension(uint8_t obu_header) {
return obu_header & 0b0'0000'100;
}
bool ObuHasSize(uint8_t obu_header) {
return obu_header & kObuSizePresentBit;
}
int ObuType(uint8_t obu_header) {
return (obu_header & 0b0'1111'000) >> 3;
}
// Given `remaining_bytes` free bytes left in a packet, returns max size of an
// OBU fragment that can fit into the packet.
// i.e. MaxFragmentSize + Leb128Size(MaxFragmentSize) <= remaining_bytes.
int MaxFragmentSize(int remaining_bytes) {
if (remaining_bytes <= 1) {
return 0;
}
for (int i = 1;; ++i) {
if (remaining_bytes < (1 << 7 * i) + i) {
return remaining_bytes - i;
}
}
}
} // namespace
RtpPacketizerAv1::RtpPacketizerAv1(rtc::ArrayView<const uint8_t> payload,
RtpPacketizer::PayloadSizeLimits limits,
VideoFrameType frame_type,
bool is_last_frame_in_picture,
bool even_distribution)
: frame_type_(frame_type),
obus_(ParseObus(payload)),
packets_(even_distribution ? PacketizeAboutEqually(obus_, limits)
: Packetize(obus_, limits)),
is_last_frame_in_picture_(is_last_frame_in_picture) {}
std::vector<RtpPacketizerAv1::Obu> RtpPacketizerAv1::ParseObus(
rtc::ArrayView<const uint8_t> payload) {
std::vector<Obu> result;
rtc::ByteBufferReader payload_reader(payload);
while (payload_reader.Length() > 0) {
Obu obu;
payload_reader.ReadUInt8(&obu.header);
obu.size = 1;
if (ObuHasExtension(obu.header)) {
if (payload_reader.Length() == 0) {
RTC_DLOG(LS_ERROR) << "Malformed AV1 input: expected extension_header, "
"no more bytes in the buffer. Offset: "
<< (payload.size() - payload_reader.Length());
return {};
}
payload_reader.ReadUInt8(&obu.extension_header);
++obu.size;
}
if (!ObuHasSize(obu.header)) {
obu.payload = rtc::MakeArrayView(
reinterpret_cast<const uint8_t*>(payload_reader.Data()),
payload_reader.Length());
payload_reader.Consume(payload_reader.Length());
} else {
uint64_t size = 0;
if (!payload_reader.ReadUVarint(&size) ||
size > payload_reader.Length()) {
RTC_DLOG(LS_ERROR) << "Malformed AV1 input: declared size " << size
<< " is larger than remaining buffer size "
<< payload_reader.Length();
return {};
}
obu.payload = rtc::MakeArrayView(
reinterpret_cast<const uint8_t*>(payload_reader.Data()), size);
payload_reader.Consume(size);
}
obu.size += obu.payload.size();
// Skip obus that shouldn't be transfered over rtp.
int obu_type = ObuType(obu.header);
if (obu_type != kObuTypeTemporalDelimiter && //
obu_type != kObuTypeTileList && //
obu_type != kObuTypePadding) {
result.push_back(obu);
}
}
return result;
}
int RtpPacketizerAv1::AdditionalBytesForPreviousObuElement(
const Packet& packet) {
if (packet.packet_size == 0) {
// Packet is still empty => no last OBU element, no need to reserve space
// for it.
return 0;
}
if (packet.num_obu_elements > kMaxNumObusToOmitSize) {
// There is so many obu elements in the packet, all of them must be
// prepended with the length field. That imply space for the length of the
// last obu element is already reserved.
return 0;
}
// No space was reserved for length field of the last OBU element, but that
// element becoming non-last, so it now requires explicit length field.
// Calculate how many bytes are needed to store the length in leb128 format.
return Leb128Size(packet.last_obu_size);
}
std::vector<RtpPacketizerAv1::Packet> RtpPacketizerAv1::Packetize(
rtc::ArrayView<const Obu> obus,
PayloadSizeLimits limits) {
std::vector<Packet> packets;
if (obus.empty()) {
return packets;
}
// Ignore certian edge cases where packets should be very small. They are
// inpractical but adds complexity to handle.
if (limits.max_payload_len - limits.last_packet_reduction_len < 3 ||
limits.max_payload_len - limits.first_packet_reduction_len < 3) {
RTC_DLOG(LS_ERROR) << "Failed to packetize AV1 frame: requested packet "
"size is unreasonable small.";
return packets;
}
// Aggregation header is present in all packets.
limits.max_payload_len -= kAggregationHeaderSize;
// Assemble packets. Push to current packet as much as it can hold before
// considering next one. That would normally cause uneven distribution across
// packets, specifically last one would be generally smaller.
packets.emplace_back(/*first_obu_index=*/0);
int packet_remaining_bytes =
limits.max_payload_len - limits.first_packet_reduction_len;
for (size_t obu_index = 0; obu_index < obus.size(); ++obu_index) {
const bool is_last_obu = obu_index == obus.size() - 1;
const Obu& obu = obus[obu_index];
// Putting `obu` into the last packet would make last obu element stored in
// that packet not last. All not last OBU elements must be prepend with the
// element length. AdditionalBytesForPreviousObuElement calculates how many
// bytes are needed to store that length.
int previous_obu_extra_size =
AdditionalBytesForPreviousObuElement(packets.back());
int min_required_size =
packets.back().num_obu_elements >= kMaxNumObusToOmitSize ? 2 : 1;
if (packet_remaining_bytes < previous_obu_extra_size + min_required_size) {
// Start a new packet.
packets.emplace_back(/*first_obu_index=*/obu_index);
packet_remaining_bytes = limits.max_payload_len;
previous_obu_extra_size = 0;
}
Packet& packet = packets.back();
// Start inserting current obu into the packet.
packet.packet_size += previous_obu_extra_size;
packet_remaining_bytes -= previous_obu_extra_size;
packet.num_obu_elements++;
bool must_write_obu_element_size =
packet.num_obu_elements > kMaxNumObusToOmitSize;
// Can fit all of the obu into the packet?
int required_bytes = obu.size;
if (must_write_obu_element_size) {
required_bytes += Leb128Size(obu.size);
}
int available_bytes = packet_remaining_bytes;
if (is_last_obu) {
// If this packet would be the last packet, available size is smaller.
if (packets.size() == 1) {
available_bytes += limits.first_packet_reduction_len;
available_bytes -= limits.single_packet_reduction_len;
} else {
available_bytes -= limits.last_packet_reduction_len;
}
}
if (required_bytes <= available_bytes) {
// Insert the obu into the packet unfragmented.
packet.last_obu_size = obu.size;
packet.packet_size += required_bytes;
packet_remaining_bytes -= required_bytes;
continue;
}
// Fragment the obu.
int max_first_fragment_size = must_write_obu_element_size
? MaxFragmentSize(packet_remaining_bytes)
: packet_remaining_bytes;
// Because available_bytes might be different than
// packet_remaining_bytes it might happen that max_first_fragment_size >=
// obu.size. Also, since checks above verified `obu` should not be put
// completely into the `packet`, leave at least 1 byte for later packet.
int first_fragment_size = std::min(obu.size - 1, max_first_fragment_size);
if (first_fragment_size == 0) {
// Rather than writing 0-size element at the tail of the packet,
// 'uninsert' the `obu` from the `packet`.
packet.num_obu_elements--;
packet.packet_size -= previous_obu_extra_size;
} else {
packet.packet_size += first_fragment_size;
if (must_write_obu_element_size) {
packet.packet_size += Leb128Size(first_fragment_size);
}
packet.last_obu_size = first_fragment_size;
}
// Add middle fragments that occupy all of the packet.
// These are easy because
// - one obu per packet imply no need to store the size of the obu.
// - this packets are nor the first nor the last packets of the frame, so
// packet capacity is always limits.max_payload_len.
int obu_offset;
for (obu_offset = first_fragment_size;
obu_offset + limits.max_payload_len < obu.size;
obu_offset += limits.max_payload_len) {
packets.emplace_back(/*first_obu_index=*/obu_index);
Packet& packet = packets.back();
packet.num_obu_elements = 1;
packet.first_obu_offset = obu_offset;
int middle_fragment_size = limits.max_payload_len;
packet.last_obu_size = middle_fragment_size;
packet.packet_size = middle_fragment_size;
}
// Add the last fragment of the obu.
int last_fragment_size = obu.size - obu_offset;
// Check for corner case where last fragment of the last obu is too large
// to fit into last packet, but may fully fit into semi-last packet.
if (is_last_obu &&
last_fragment_size >
limits.max_payload_len - limits.last_packet_reduction_len) {
// Split last fragments into two.
RTC_DCHECK_GE(last_fragment_size, 2);
// Try to even packet sizes rather than payload sizes across the last
// two packets.
int semi_last_fragment_size =
(last_fragment_size + limits.last_packet_reduction_len) / 2;
// But leave at least one payload byte for the last packet to avoid
// weird scenarios where size of the fragment is zero and rtp payload has
// nothing except for an aggregation header.
if (semi_last_fragment_size >= last_fragment_size) {
semi_last_fragment_size = last_fragment_size - 1;
}
last_fragment_size -= semi_last_fragment_size;
packets.emplace_back(/*first_obu_index=*/obu_index);
Packet& packet = packets.back();
packet.num_obu_elements = 1;
packet.first_obu_offset = obu_offset;
packet.last_obu_size = semi_last_fragment_size;
packet.packet_size = semi_last_fragment_size;
obu_offset += semi_last_fragment_size;
}
packets.emplace_back(/*first_obu_index=*/obu_index);
Packet& last_packet = packets.back();
last_packet.num_obu_elements = 1;
last_packet.first_obu_offset = obu_offset;
last_packet.last_obu_size = last_fragment_size;
last_packet.packet_size = last_fragment_size;
packet_remaining_bytes = limits.max_payload_len - last_fragment_size;
}
return packets;
}
std::vector<RtpPacketizerAv1::Packet> RtpPacketizerAv1::PacketizeAboutEqually(
rtc::ArrayView<const Obu> obus,
PayloadSizeLimits limits) {
std::vector<Packet> packets = Packetize(obus, limits);
if (packets.size() <= 1) {
return packets;
}
size_t packet_index = 0;
size_t packet_size_left_unused = 0;
for (const auto& packet : packets) {
// Every packet has to have an aggregation header of size
// kAggregationHeaderSize.
int available_bytes = limits.max_payload_len - kAggregationHeaderSize;
if (packet_index == 0) {
available_bytes -= limits.first_packet_reduction_len;
} else if (packet_index == packets.size() - 1) {
available_bytes -= limits.last_packet_reduction_len;
}
if (available_bytes >= packet.packet_size) {
packet_size_left_unused += (available_bytes - packet.packet_size);
}
packet_index++;
}
if (packet_size_left_unused >
packets.size() * kMinBytesSavedPerPacketWithEvenDistribution) {
// Calculate new limits with a reduced max_payload_len.
size_t size_reduction = packet_size_left_unused / packets.size();
RTC_DCHECK_GT(limits.max_payload_len, size_reduction);
RTC_DCHECK_GT(size_reduction, kBytesOverheadEvenDistribution);
limits.max_payload_len -= (size_reduction - kBytesOverheadEvenDistribution);
if (limits.max_payload_len - limits.last_packet_reduction_len < 3 ||
limits.max_payload_len - limits.first_packet_reduction_len < 3) {
return packets;
}
std::vector<Packet> packets_even = Packetize(obus, limits);
// The number of packets should not change in the second pass. If it does,
// conservatively return the original packets.
if (packets_even.size() == packets.size()) {
return packets_even;
}
RTC_LOG(LS_WARNING) << "AV1 even distribution caused a regression in "
"number of packets from "
<< packets.size() << " to " << packets_even.size();
}
return packets;
}
uint8_t RtpPacketizerAv1::AggregationHeader() const {
const Packet& packet = packets_[packet_index_];
uint8_t aggregation_header = 0;
// Set Z flag: first obu element is continuation of the previous OBU.
bool first_obu_element_is_fragment = packet.first_obu_offset > 0;
if (first_obu_element_is_fragment)
aggregation_header |= (1 << 7);
// Set Y flag: last obu element will be continuated in the next packet.
int last_obu_offset =
packet.num_obu_elements == 1 ? packet.first_obu_offset : 0;
bool last_obu_is_fragment =
last_obu_offset + packet.last_obu_size <
obus_[packet.first_obu + packet.num_obu_elements - 1].size;
if (last_obu_is_fragment)
aggregation_header |= (1 << 6);
// Set W field: number of obu elements in the packet (when not too large).
if (packet.num_obu_elements <= kMaxNumObusToOmitSize)
aggregation_header |= packet.num_obu_elements << 4;
// Set N flag: beginning of a new coded video sequence.
// Encoder may produce key frame without a sequence header, thus double check
// incoming frame includes the sequence header. Since Temporal delimiter is
// already filtered out, sequence header should be the first obu when present.
if (frame_type_ == VideoFrameType::kVideoFrameKey && packet_index_ == 0 &&
ObuType(obus_.front().header) == kObuTypeSequenceHeader) {
aggregation_header |= (1 << 3);
}
return aggregation_header;
}
bool RtpPacketizerAv1::NextPacket(RtpPacketToSend* packet) {
if (packet_index_ >= packets_.size()) {
return false;
}
const Packet& next_packet = packets_[packet_index_];
RTC_DCHECK_GT(next_packet.num_obu_elements, 0);
RTC_DCHECK_LT(next_packet.first_obu_offset,
obus_[next_packet.first_obu].size);
RTC_DCHECK_LE(
next_packet.last_obu_size,
obus_[next_packet.first_obu + next_packet.num_obu_elements - 1].size);
uint8_t* const rtp_payload =
packet->AllocatePayload(kAggregationHeaderSize + next_packet.packet_size);
uint8_t* write_at = rtp_payload;
*write_at++ = AggregationHeader();
int obu_offset = next_packet.first_obu_offset;
// Store all OBU elements except the last one.
for (int i = 0; i < next_packet.num_obu_elements - 1; ++i) {
const Obu& obu = obus_[next_packet.first_obu + i];
size_t fragment_size = obu.size - obu_offset;
write_at += WriteLeb128(fragment_size, write_at);
if (obu_offset == 0) {
*write_at++ = obu.header & ~kObuSizePresentBit;
}
if (obu_offset <= 1 && ObuHasExtension(obu.header)) {
*write_at++ = obu.extension_header;
}
int payload_offset =
std::max(0, obu_offset - (ObuHasExtension(obu.header) ? 2 : 1));
size_t payload_size = obu.payload.size() - payload_offset;
if (!obu.payload.empty() && payload_size > 0) {
memcpy(write_at, obu.payload.data() + payload_offset, payload_size);
}
write_at += payload_size;
// All obus are stored from the beginning, except, may be, the first one.
obu_offset = 0;
}
// Store the last OBU element.
const Obu& last_obu =
obus_[next_packet.first_obu + next_packet.num_obu_elements - 1];
int fragment_size = next_packet.last_obu_size;
RTC_DCHECK_GT(fragment_size, 0);
if (next_packet.num_obu_elements > kMaxNumObusToOmitSize) {
write_at += WriteLeb128(fragment_size, write_at);
}
if (obu_offset == 0 && fragment_size > 0) {
*write_at++ = last_obu.header & ~kObuSizePresentBit;
--fragment_size;
}
if (obu_offset <= 1 && ObuHasExtension(last_obu.header) &&
fragment_size > 0) {
*write_at++ = last_obu.extension_header;
--fragment_size;
}
RTC_DCHECK_EQ(write_at - rtp_payload + fragment_size,
kAggregationHeaderSize + next_packet.packet_size);
int payload_offset =
std::max(0, obu_offset - (ObuHasExtension(last_obu.header) ? 2 : 1));
memcpy(write_at, last_obu.payload.data() + payload_offset, fragment_size);
write_at += fragment_size;
RTC_DCHECK_EQ(write_at - rtp_payload,
kAggregationHeaderSize + next_packet.packet_size);
++packet_index_;
bool is_last_packet_in_frame = packet_index_ == packets_.size();
packet->SetMarker(is_last_packet_in_frame && is_last_frame_in_picture_);
return true;
}
} // namespace webrtc