libavcodec/h264enc.c

   1 /*
   2  * H.264 encoder
   3  *
   4  * FFmpeg is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU Lesser General Public
   6  * License as published by the Free Software Foundation; either
   7  * version 2.1 of the License, or (at your option) any later version.
   8  *
   9  * FFmpeg is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * Lesser General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Lesser General Public
  15  * License along with FFmpeg; if not, write to the Free Software
  16  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  17  */
  18
  19
  20 #include "libavutil/common.h"
  21 #include "bitstream.h"
  22 #include "mpegvideo.h"
  23 #include "h264data.h"
  24
  25 /**
  26  * Write out the provided data into a NAL unit.
  27  * @param nal_ref_idc NAL reference IDC
  28  * @param nal_unit_type NAL unit payload type
  29  * @param dest the target buffer, dst+1 == src is allowed as a special case
  30  * @param destsize the length of the dst array
  31  * @param b2 the data which should be escaped
  32  * @returns pointer to current position in the output buffer or NULL if an error occurred
  33  */
  34 static uint8_t *h264_write_nal_unit(int nal_ref_idc, int nal_unit_type, uint8_t *dest, int *destsize,
  35                           PutBitContext *b2)
  36 {
  37     PutBitContext b;
  38     int i, destpos, rbsplen, escape_count;
  39     uint8_t *rbsp;
  40
  41     if (nal_unit_type != NAL_END_STREAM)
  42         put_bits(b2,1,1); // rbsp_stop_bit
  43
  44     // Align b2 on a byte boundary
  45     align_put_bits(b2);
  46     rbsplen = put_bits_count(b2)/8;
  47     flush_put_bits(b2);
  48     rbsp = b2->buf;
  49
  50     init_put_bits(&b,dest,*destsize);
  51
  52     put_bits(&b,16,0);
  53     put_bits(&b,16,0x01);
  54
  55     put_bits(&b,1,0); // forbidden zero bit
  56     put_bits(&b,2,nal_ref_idc); // nal_ref_idc
  57     put_bits(&b,5,nal_unit_type); // nal_unit_type
  58
  59     flush_put_bits(&b);
  60
  61     destpos = 5;
  62     escape_count= 0;
  63
  64     for (i=0; i<rbsplen; i+=2)
  65     {
  66         if (rbsp[i]) continue;
  67         if (i>0 && rbsp[i-1]==0)
  68             i--;
  69         if (i+2<rbsplen && rbsp[i+1]==0 && rbsp[i+2]<=3)
  70         {
  71             escape_count++;
  72             i+=2;
  73         }
  74     }
  75
  76     if(escape_count==0)
  77     {
  78         if(dest+destpos != rbsp)
  79         {
  80             memcpy(dest+destpos, rbsp, rbsplen);
  81             *destsize -= (rbsplen+destpos);
  82         }
  83         return dest+rbsplen+destpos;
  84     }
  85
  86     if(rbsplen + escape_count + 1> *destsize)
  87     {
  88         av_log(NULL, AV_LOG_ERROR, "Destination buffer too small!\n");
  89         return NULL;
  90     }
  91
  92     // this should be damn rare (hopefully)
  93     for (i = 0 ; i < rbsplen ; i++)
  94     {
  95         if (i + 2 < rbsplen && (rbsp[i] == 0 && rbsp[i+1] == 0 && rbsp[i+2] < 4))
  96         {
  97             dest[destpos++] = rbsp[i++];
  98             dest[destpos++] = rbsp[i];
  99             dest[destpos++] = 0x03; // emulation prevention byte
 100         }
 101         else
 102             dest[destpos++] = rbsp[i];
 103     }
 104     *destsize -= destpos;
 105     return dest+destpos;
 106 }
 107