H264PacketBuffer

• m98代码：
• H264PacketBuffer 类似于PacketBuffer ，但仅用于H264

// The H264PacketBuffer does the same job as the PacketBuffer but for H264
// only. To make it fit in with surronding code the PacketBuffer input/output
// classes are used.

• 因此，使用了相同的代码：

  using Packet = video_coding::PacketBuffer::Packet;
  using InsertResult = video_coding::PacketBuffer::InsertResult