老范的自言自语 Walter's Solo

H.264 packetization types

March 28, 2023 by walter

在视频会议中 H264 的 NAL: Network Abstraction Layer 包类型基本上有三种
1) Single NAL unit 单个 NALU
2) STAP-A: Single Time Aggregation Packet 单时间聚合包
3) FU-A: Fragmentation Unit Packet 片段单元包

// The packetization types that we support: single, aggregated, and fragmented.
enum H264PacketizationTypes {
  kH264SingleNalu,  // This packet contains a single NAL unit.
  kH264StapA,       // This packet contains STAP-A (single time
                    // aggregation) packets. If this packet has an
                    // associated NAL unit type, it'll be for the
                    // first such aggregated packet.
  kH264FuA,         // This packet contains a FU-A (fragmentation
                    // unit) packet, meaning it is a part of a frame
                    // that was too large to fit into a single packet.
};

// Packetization modes are defined in RFC 6184 section 6
// Due to the structure containing this being initialized with zeroes
// in some places, and mode 1 being default, mode 1 needs to have the value
// zero. https://crbug.com/webrtc/6803
enum class H264PacketizationMode {
  NonInterleaved = 0,  // Mode 1 - STAP-A, FU-A is allowed
  SingleNalUnit        // Mode 0 - only single NALU allowed
};

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