| /* |
| * 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 |
