func: static int gif_image_write_image(AVCodecContext *avctx,
  
                                   uint8_t **bytestream, uint8_t *end,
  
                                   const uint32_t *palette,
  
                                   const uint8_t *buf, const int linesize,
  
                                   AVPacket *pkt)
  
  {
  
      GIFContext *s = avctx->priv_data;
  
      int len = 0, height = avctx->height, width = avctx->width, x, y;
  
      int x_start = 0, y_start = 0, trans = s->transparent_index;
  
      int honor_transparency = (s->flags & GF_TRANSDIFF) && s->last_frame;
  
      const uint8_t *ptr;
  
  
  
      /* Crop image */
  
      if ((s->flags & GF_OFFSETTING) && s->last_frame && !palette) {
  
          const uint8_t *ref = s->last_frame->data[0];
  
          const int ref_linesize = s->last_frame->linesize[0];
  
          int x_end = avctx->width  - 1,
  
              y_end = avctx->height - 1;
  
  
  
          /* skip common lines */
  
          while (y_start < y_end) {
  
              if (memcmp(ref + y_start*ref_linesize, buf + y_start*linesize, width))
  
                  break;
  
              y_start++;
  
          }
  
          while (y_end > y_start) {
  
              if (memcmp(ref + y_end*ref_linesize, buf + y_end*linesize, width))
  
                  break;
  
              y_end--;
  
          }
  
          height = y_end + 1 - y_start;
  
  
  
          /* skip common columns */
  
          while (x_start < x_end) {
  
              int same_column = 1;
  
              for (y = y_start; y <= y_end; y++) {
  
                  if (ref[y*ref_linesize + x_start] != buf[y*linesize + x_start]) {
  
                      same_column = 0;
  
                      break;
  
                  }
  
              }
  
              if (!same_column)
  
                  break;
  
              x_start++;
  
          }
  
          while (x_end > x_start) {
  
              int same_column = 1;
  
              for (y = y_start; y <= y_end; y++) {
  
                  if (ref[y*ref_linesize + x_end] != buf[y*linesize + x_end]) {
  
                      same_column = 0;
  
                      break;
  
                  }
  
              }
  
              if (!same_column)
  
                  break;
  
              x_end--;
  
          }
  
          width = x_end + 1 - x_start;
  
  
  
          av_log(avctx, AV_LOG_DEBUG,"%dx%d image at pos (%d;%d) [area:%dx%d]\n",
  
                 width, height, x_start, y_start, avctx->width, avctx->height);
  
      }
  
  
  
      /* image block */
  
      bytestream_put_byte(bytestream, GIF_IMAGE_SEPARATOR);
  
      bytestream_put_le16(bytestream, x_start);
  
      bytestream_put_le16(bytestream, y_start);
  
      bytestream_put_le16(bytestream, width);
  
      bytestream_put_le16(bytestream, height);
  
  
  
      if (!palette) {
  
          bytestream_put_byte(bytestream, 0x00); /* flags */
  
      } else {
  
          unsigned i;
  
          bytestream_put_byte(bytestream, 1<<7 | 0x7); /* flags */
  
          for (i = 0; i < AVPALETTE_COUNT; i++) {
  
              const uint32_t v = palette[i];
  
              bytestream_put_be24(bytestream, v);
  
          }
  
      }
  
  
  
      if (honor_transparency && trans < 0) {
  
          trans = pick_palette_entry(buf + y_start*linesize + x_start,
  
                                     linesize, width, height);
  
          if (trans < 0) { // TODO, patch welcome
  
              av_log(avctx, AV_LOG_DEBUG, "No available color, can not use transparency\n");
  
          } else {
  
              uint8_t *pal_exdata = s->pal_exdata;
  
              if (!pal_exdata)
  
                  pal_exdata = av_packet_new_side_data(pkt, AV_PKT_DATA_PALETTE, AVPALETTE_SIZE);
  
              if (!pal_exdata)
  
                  return AVERROR(ENOMEM);
  
              memcpy(pal_exdata, s->palette, AVPALETTE_SIZE);
  
              pal_exdata[trans*4 + 3*!HAVE_BIGENDIAN] = 0x00;
  
          }
  
      }
  
      if (trans < 0)
  
          honor_transparency = 0;
  
  
  
      bytestream_put_byte(bytestream, 0x08);
  
  
  
      ff_lzw_encode_init(s->lzw, s->buf, 2 * width * height,
  
                         12, FF_LZW_GIF, put_bits);
  
  
  
      ptr = buf + y_start*linesize + x_start;
  
      if (honor_transparency) {
  
          const int ref_linesize = s->last_frame->linesize[0];
  
          const uint8_t *ref = s->last_frame->data[0] + y_start*ref_linesize + x_start;
  
  
  
          for (y = 0; y < height; y++) {
  
              memcpy(s->tmpl, ptr, width);
  
              for (x = 0; x < width; x++)
  
                  if (ref[x] == ptr[x])
  
                      s->tmpl[x] = trans;
  
              len += ff_lzw_encode(s->lzw, s->tmpl, width);
  
              ptr += linesize;
  
              ref += ref_linesize;
  
          }
  
      } else {
  
          for (y = 0; y < height; y++) {
  
              len += ff_lzw_encode(s->lzw, ptr, width);
  
              ptr += linesize;
  
          }
  
      }
  
      len += ff_lzw_encode_flush(s->lzw, flush_put_bits);
  
  
  
      ptr = s->buf;
  
      while (len > 0) {
  
          int size = FFMIN(255, len);
  
          bytestream_put_byte(bytestream, size);
  
          if (end - *bytestream < size)
  
              return -1;
  
          bytestream_put_buffer(bytestream, ptr, size);
  
          ptr += size;
  
          len -= size;
  
      }
  
      bytestream_put_byte(bytestream, 0x00); /* end of image block */
  
      return 0;
  
  }
  