public static SliceType GetSliceTypeFromH264Payload(byte[] payload)
{
int countToZero = payload.Length;
BinaryReader reader = new BinaryReader(new MemoryStream(payload));
while (countToZero > 4)
{
ulong naluLen = BitReader.GetUIntValue(reader.ReadUInt32());
long nextPos = reader.BaseStream.Position + (long)naluLen;
//Table 7-1 – NAL unit type codes
//nal_unit_type Content of NAL unit and RBSP syntax structure C
//0 Unspecified
//1 Coded slice of a non-IDR picture
// slice_layer_without_partitioning_rbsp( )
//2 Coded slice data partition A
// slice_data_partition_a_layer_rbsp( )
//3 Coded slice data partition B
// slice_data_partition_b_layer_rbsp( )
//4 Coded slice data partition C
// slice_data_partition_c_layer_rbsp( )
//5 Coded slice of an IDR picture
// slice_layer_without_partitioning_rbsp( )
//6 Supplemental enhancement information (SEI)
// sei_rbsp( )
//7 Sequence parameter set
// seq_parameter_set_rbsp( )
//8 Picture parameter set
// pic_parameter_set_rbsp( )
//9 Access unit delimiter
// access_unit_delimiter_rbsp( )
//10 End of sequence
// end_of_seq_rbsp( )
//11 End of stream
// end_of_stream_rbsp( )
//12 Filler data
// filler_data_rbsp( )
//13..23 Reserved
//24..31 Unspecified
uint typ = reader.ReadByte() & 0x1Fu;
if ((naluLen > (ulong)countToZero) || (naluLen < 2))
{
return(SliceType.Unknown);
}
// NALU type 5 is IDR picture
if ((typ == 5u) || (typ == 1u))
{
// when the type == 5 its an IDR picture, now slice_type shall be equal to
// 2, 4, 7, or 9 (I or SI);
// slice_type specified the coding type of the slice according to Table 7-6: e.g. P, B, I, SP, SI
//
// nalu header:
// first_mb_in_slice = get_ue_golomb
// slice_type = get_ue_golomb
//
// http://www.iitk.ac.in/mwn/vaibhav/Vaibhav%20Sharma_files/h.264_standard_document.pdf
//Table 7-3 – Name association to slice_type
//0 P (P slice)
//1 B (B slice)
//2 I (I slice)
//3 SP (SP slice)
//4 SI (SI slice)
//5 P (P slice)
//6 B (B slice)
//7 I (I slice)
//8 SP (SP slice)
//9 SI (SI slice)
BitReader br = new BitReader(reader.BaseStream);
uint first_mb_in_slice = br.DecodeUnsignedExpGolomb();
uint slice_type = br.DecodeUnsignedExpGolomb();
uint pic_parameter_set_id = br.DecodeUnsignedExpGolomb();
uint frame_num = br.DecodeUnsignedExpGolomb();
if (typ == 5u)
{
return(SliceType.IFrame);
}
if (slice_type == 1 || slice_type == 6)
{
return(SliceType.BFrame);
}
return(SliceType.DFrame);
}
countToZero -= ((int)naluLen + 4);
reader.BaseStream.Position = nextPos;
}
return(SliceType.Unknown);
}
