func: static int encode_apng(AVCodecContext *avctx, AVPacket *pkt,
  
                         const AVFrame *pict, int *got_packet)
  
  {
  
      PNGEncContext *s = avctx->priv_data;
  
      int ret;
  
      int enc_row_size;
  
      size_t max_packet_size;
  
      APNGFctlChunk fctl_chunk = {0};
  
  
  
      if (pict && avctx->codec_id == AV_CODEC_ID_APNG && s->color_type == PNG_COLOR_TYPE_PALETTE) {
  
          uint32_t checksum = ~av_crc(av_crc_get_table(AV_CRC_32_IEEE_LE), ~0U, pict->data[1], 256 * sizeof(uint32_t));
  
  
  
          if (avctx->frame_number == 0) {
  
              s->palette_checksum = checksum;
  
          } else if (checksum != s->palette_checksum) {
  
              av_log(avctx, AV_LOG_ERROR,
  
                     "Input contains more than one unique palette. APNG does not support multiple palettes.\n");
  
              return -1;
  
          }
  
      }
  
  
  
      enc_row_size    = deflateBound(&s->zstream, (avctx->width * s->bits_per_pixel + 7) >> 3);
  
      max_packet_size =
  
          AV_INPUT_BUFFER_MIN_SIZE + // headers
  
          avctx->height * (
  
              enc_row_size +
  
              (4 + 12) * (((int64_t)enc_row_size + IOBUF_SIZE - 1) / IOBUF_SIZE) // fdAT * ceil(enc_row_size / IOBUF_SIZE)
  
          );
  
      if (max_packet_size > INT_MAX)
  
          return AVERROR(ENOMEM);
  
  
  
      if (avctx->frame_number == 0) {
  
          if (!pict)
  
              return AVERROR(EINVAL);
  
  
  
          s->bytestream = avctx->extradata = av_malloc(FF_MIN_BUFFER_SIZE);
  
          if (!avctx->extradata)
  
              return AVERROR(ENOMEM);
  
  
  
          ret = encode_headers(avctx, pict);
  
          if (ret < 0)
  
              return ret;
  
  
  
          avctx->extradata_size = s->bytestream - avctx->extradata;
  
  
  
          s->last_frame_packet = av_malloc(max_packet_size);
  
          if (!s->last_frame_packet)
  
              return AVERROR(ENOMEM);
  
      } else if (s->last_frame) {
  
          ret = ff_alloc_packet2(avctx, pkt, max_packet_size, 0);
  
          if (ret < 0)
  
              return ret;
  
  
  
          memcpy(pkt->data, s->last_frame_packet, s->last_frame_packet_size);
  
          pkt->size = s->last_frame_packet_size;
  
          pkt->pts = pkt->dts = s->last_frame->pts;
  
      }
  
  
  
      if (pict) {
  
          s->bytestream_start =
  
          s->bytestream       = s->last_frame_packet;
  
          s->bytestream_end   = s->bytestream + max_packet_size;
  
  
  
          // We're encoding the frame first, so we have to do a bit of shuffling around
  
          // to have the image data write to the correct place in the buffer
  
          fctl_chunk.sequence_number = s->sequence_number;
  
          ++s->sequence_number;
  
          s->bytestream += 26 + 12;
  
  
  
          ret = apng_encode_frame(avctx, pict, &fctl_chunk, &s->last_frame_fctl);
  
          if (ret < 0)
  
              return ret;
  
  
  
          fctl_chunk.delay_num = 0; // delay filled in during muxing
  
          fctl_chunk.delay_den = 0;
  
      } else {
  
          s->last_frame_fctl.dispose_op = APNG_DISPOSE_OP_NONE;
  
      }
  
  
  
      if (s->last_frame) {
  
          uint8_t* last_fctl_chunk_start = pkt->data;
  
          uint8_t buf[26];
  
  
  
          AV_WB32(buf + 0, s->last_frame_fctl.sequence_number);
  
          AV_WB32(buf + 4, s->last_frame_fctl.width);
  
          AV_WB32(buf + 8, s->last_frame_fctl.height);
  
          AV_WB32(buf + 12, s->last_frame_fctl.x_offset);
  
          AV_WB32(buf + 16, s->last_frame_fctl.y_offset);
  
          AV_WB16(buf + 20, s->last_frame_fctl.delay_num);
  
          AV_WB16(buf + 22, s->last_frame_fctl.delay_den);
  
          buf[24] = s->last_frame_fctl.dispose_op;
  
          buf[25] = s->last_frame_fctl.blend_op;
  
          png_write_chunk(&last_fctl_chunk_start, MKTAG('f', 'c', 'T', 'L'), buf, 26);
  
  
  
          *got_packet = 1;
  
      }
  
  
  
      if (pict) {
  
          if (!s->last_frame) {
  
              s->last_frame = av_frame_alloc();
  
              if (!s->last_frame)
  
                  return AVERROR(ENOMEM);
  
          } else if (s->last_frame_fctl.dispose_op != APNG_DISPOSE_OP_PREVIOUS) {
  
              if (!s->prev_frame) {
  
                  s->prev_frame = av_frame_alloc();
  
                  if (!s->prev_frame)
  
                      return AVERROR(ENOMEM);
  
  
  
                  s->prev_frame->format = pict->format;
  
                  s->prev_frame->width = pict->width;
  
                  s->prev_frame->height = pict->height;
  
                  if ((ret = av_frame_get_buffer(s->prev_frame, 32)) < 0)
  
                      return ret;
  
              }
  
  
  
              // Do disposal, but not blending
  
              memcpy(s->prev_frame->data[0], s->last_frame->data[0],
  
                     s->last_frame->linesize[0] * s->last_frame->height);
  
              if (s->last_frame_fctl.dispose_op == APNG_DISPOSE_OP_BACKGROUND) {
  
                  uint32_t y;
  
                  uint8_t bpp = (s->bits_per_pixel + 7) >> 3;
  
                  for (y = s->last_frame_fctl.y_offset; y < s->last_frame_fctl.y_offset + s->last_frame_fctl.height; ++y) {
  
                      size_t row_start = s->last_frame->linesize[0] * y + bpp * s->last_frame_fctl.x_offset;
  
                      memset(s->prev_frame->data[0] + row_start, 0, bpp * s->last_frame_fctl.width);
  
                  }
  
              }
  
          }
  
  
  
          av_frame_unref(s->last_frame);
  
          ret = av_frame_ref(s->last_frame, (AVFrame*)pict);
  
          if (ret < 0)
  
              return ret;
  
  
  
          s->last_frame_fctl = fctl_chunk;
  
          s->last_frame_packet_size = s->bytestream - s->bytestream_start;
  
      } else {
  
          av_frame_free(&s->last_frame);
  
      }
  
  
  
      return 0;
  
  }
  