The larger the value, the more important it is Used to indicate the importance of the current NALU. The NALU Header consists of three parts, forbidden_bit(1bit)，nal_ref_idc (2bits) stands for priority, nal_unit_type (5bits) represents the type of the NALU.ġ bit, H264 specifies that this bit must be 0 In H264, syntactic elements are organized into five levels: sequence, image (frame), slice, macroblock and sub macroblock. The first frame of an IDR sequence is called an ID frame (instant decoding refresh). M specifies the distance between I frames and P frames, and N specifies the distance between two I frames. GOP generally has two numbers, such as M = 3 and N = 12. GOP is a picture group, and a GOP is a group of continuous pictures. The Start Code is used to mark the beginning of a NALU unit and must be "00 01" H264 original code stream is composed of one NALU (real unit), one NALU = a group of NALU header information corresponding to video coding + a Raw Byte Sequence Payload (RBSP).Īn original H.264 NALU unit is usually composed of.
PPS picture parameter set, the parameter set of an image (PPS) includes the information of all slices of an image. SPS sequence parameter set, the sequence parameter set (SPS) includes all the information of an image sequence, and SPS stores a set of global parameters of Coded video sequence. Strong network adaptability: H.264 provides a Network Abstraction Layer, so that H.264 files can be easily transmitted on different networks (such as Internet, CDMA, GPRS, WCDMA, CDMA2000, etc.). Strong fault tolerance: H.264 provides a necessary tool to solve packet loss and other errors that are easy to occur in unstable network environment.Ĥ. High quality images: H.264 can provide continuous and smooth high-quality images (DVD quality).ģ. Low Bit Rate: compared with MPEG2 and MPEG4 ASP compression technologies, under the same image quality, the amount of data compressed by H.264 technology is only 1 / 8 of MPEG2 and 1 / 3 of MPEG4.Ģ. There are also Instantaneous Decoding Refresh (IDR), Hypothetical Reference Decoder (HRD), and Hypothetical Stream Scheduler (HSS).ġ. The main parts of H264 standard include Access Unit delimiter, SEI, primary coded picture and Redundant Coded Picture.
This standard is usually called H.264/AVC (or AVC/H.264 or H.264/MPEG-4 AVC or MPEG-4/H.264 AVC) and clearly describes its developers in both aspects. 264, also the tenth part of MPEG-4, is a highly compressed digital video codec standard proposed by the Joint Video Team (JVT, Joint Video Team) jointly composed of ITU-T video coding expert group (VCEG) and ISO/IEC dynamic image expert group (MPEG). I got to comment these lines to make it work.FFmpeg decoding H264 is mainly divided into three steps: one is to obtain the decoder, the other is to send H264 NALU to the decoder, and the third is to obtain the decoded YUV and other data from the decoder.
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