libavcodec/vaapi_encode_h26x.c

   1 /*
   2  * This file is part of Libav.
   3  *
   4  * Libav 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  * Libav 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 Libav; if not, write to the Free Software
  16  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  17  */
  18
  19 #include <stdint.h>
  20
  21 #include "vaapi_encode_h26x.h"
  22
  23 int ff_vaapi_encode_h26x_nal_unit_to_byte_stream(uint8_t *dst, size_t *dst_bit_len,
  24                                                  uint8_t *src, size_t src_bit_len)
  25 {
  26     size_t dp, sp;
  27     int zero_run = 0;
  28     size_t dst_len = *dst_bit_len / 8;
  29     size_t src_len = (src_bit_len + 7) / 8;
  30     int trailing_zeroes = src_len * 8 - src_bit_len;
  31
  32     if (dst_len < src_len + 4) {
  33         // Definitely doesn't fit.
  34         goto fail;
  35     }
  36
  37     // Start code.
  38     dst[0] = dst[1] = dst[2] = 0;
  39     dst[3] = 1;
  40     dp = 4;
  41
  42     for (sp = 0; sp < src_len; sp++) {
  43         if (dp >= dst_len)
  44             goto fail;
  45         if (zero_run < 2) {
  46             if (src[sp] == 0)
  47                 ++zero_run;
  48             else
  49                 zero_run = 0;
  50         } else {
  51             if ((src[sp] & ~3) == 0) {
  52                 // emulation_prevention_three_byte
  53                 dst[dp++] = 3;
  54                 if (dp >= dst_len)
  55                     goto fail;
  56             }
  57             zero_run = src[sp] == 0;
  58         }
  59         dst[dp++] = src[sp];
  60     }
  61
  62     *dst_bit_len = 8 * dp - trailing_zeroes;
  63     return 0;
  64
  65 fail:
  66     *dst_bit_len = 0;
  67     return AVERROR(ENOSPC);
  68 }