H264 i/p/b Frame Type Judging

Here we first explain the structure of the following H264:

01/00 01->nal (1bytes)->slice-> macro block, motion estimation vector, XX.

If a prefix appears in the body of the H264, it is changed from 00 00 00 01/00 00 01 to 00 03 00 00 01/00 03 00 01.

We see commonly used naltype like sps= 0x07 pps= 0x08 sei = 0x06 i/p/b= 0x01/0x05 that is to say only Naltype = 0x01/0x05 is not judged out i/p/b frame type, need to go to the slice layer to determine the use of "Entropy Code" specific "Entropy coding" content, please see: "H." Chinese version of "PDF".

Below is the deduction of the FFmpeg source to determine the implementation of the i/p/b frame type:

[CPP]  View plain copy int getframetype (nalu_t * nal)    {        bs_t s;       int frame_type = 0;        unsigned char * OneFrameBuf_H264 = NULL ;       if  (oneframebuf_h264 =  (unsigned char *) calloc (Nal->len  + 4,sizeof (Unsigned char))  == null)        {            printf ("error malloc oneframebuf_h264\n");            return getchar ();        }       if  (nal->startcodeprefix_len == 3)         {           oneframebuf_h264[0]  = 0x00;           OneFrameBuf_H264[1] = 0x00;           OneFrameBuf_H264[2] = 0x01;            memcpy (Oneframebuf_h264 + 3,nal->buf,nal->len);        }       else if  (nal->startcodeprefix_ len == 4)        {            OneFrameBuf_H264[0] = 0x00;            oneframebuf_h264[1] = 0x00;           oneframebuf_ h264[2] = 0x00;           OneFrameBuf_H264[3]  = 0x01;           memcpy (OneFrameBuf_H264 + 4, Nal->buf,nal-&gT;len);       }       else        {           printf ("H264 read error. \ n ");       }       bs_init ( &s,oneframebuf _h264 + nal->startcodeprefix_len + 1  ,nal->len - 1 );              if  (Nal->nal_unit_type == nal_ slice | |  nal->nal_unit_type ==  NAL_SLICE_IDR )        {            /* i_first_mb */            bs_read_ue ( &s );            /* picture type */           frame _type =&Nbsp; bs_read_ue ( &s );           switch ( Frame_type)            {            case 0: case 5: /* P */                nal->Frametype = FRAME_P;                break;            case 1: case 6: /* B */                nal->Frametype = FRAME_B;                break;            case 3: case 8: /* SP */                nal->frametype = frame_p;