text: /*
   * APNG muxer
   * Copyright (c) 2015 Donny Yang
   *
   * first version by Donny Yang <work@kota.moe>
   *
   * This file is part of FFmpeg.
   *
   * FFmpeg is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Lesser General Public
   * License as published by the Free Software Foundation; either
   * version 2.1 of the License, or (at your option) any later version.
   *
   * FFmpeg is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * Lesser General Public License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with FFmpeg; if not, write to the Free Software
   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
   */
  
  #include "avformat.h"
  #include "internal.h"
  #include "libavutil/avassert.h"
  #include "libavutil/crc.h"
  #include "libavutil/intreadwrite.h"
  #include "libavutil/log.h"
  #include "libavutil/opt.h"
  #include "libavcodec/png.h"
  #include "libavcodec/apng.h"
  
  typedef struct APNGMuxContext {
      AVClass *class;
  
      uint32_t plays;
      AVRational last_delay;
  
      uint64_t acTL_offset;
      uint32_t frame_number;
  
      AVPacket *prev_packet;
      AVRational prev_delay;
  
      int framerate_warned;
  
      uint8_t *extra_data;
      int extra_data_size;
  } APNGMuxContext;
  
  static uint8_t *apng_find_chunk(uint32_t tag, uint8_t *buf, size_t length)
  {
      size_t b;
      for (b = 0; b < length; b += AV_RB32(buf + b) + 12)
          if (AV_RB32(&buf[b + 4]) == tag)
              return &buf[b];
      return NULL;
  }
  
  static void apng_write_chunk(AVIOContext *io_context, uint32_t tag,
                               uint8_t *buf, size_t length)
  {
      const AVCRC *crc_table = av_crc_get_table(AV_CRC_32_IEEE_LE);
      uint32_t crc = ~0U;
      uint8_t tagbuf[4];
  
      av_assert0(crc_table);
  
      avio_wb32(io_context, length);
      AV_WB32(tagbuf, tag);
      crc = av_crc(crc_table, crc, tagbuf, 4);
      avio_wb32(io_context, tag);
      if (length > 0) {
          crc = av_crc(crc_table, crc, buf, length);
          avio_write(io_context, buf, length);
      }
      avio_wb32(io_context, ~crc);
  }
  
  static int apng_write_header(AVFormatContext *format_context)
  {
      APNGMuxContext *apng = format_context->priv_data;
      AVCodecParameters *par = format_context->streams[0]->codecpar;
  
      if (format_context->nb_streams != 1 ||
          format_context->streams[0]->codecpar->codec_type != AVMEDIA_TYPE_VIDEO ||
          format_context->streams[0]->codecpar->codec_id   != AV_CODEC_ID_APNG) {
          av_log(format_context, AV_LOG_ERROR,
                 "APNG muxer supports only a single video APNG stream.\n");
          return AVERROR(EINVAL);
      }
  
      if (apng->last_delay.num > USHRT_MAX || apng->last_delay.den > USHRT_MAX) {
          av_reduce(&apng->last_delay.num, &apng->last_delay.den,
                    apng->last_delay.num, apng->last_delay.den, USHRT_MAX);
          av_log(format_context, AV_LOG_WARNING,
                 "Last frame delay is too precise. Reducing to %d/%d (%f).\n",
                 apng->last_delay.num, apng->last_delay.den, (double)apng->last_delay.num / apng->last_delay.den);
      }
  
      avio_wb64(format_context->pb, PNGSIG);
      // Remaining headers are written when they are copied from the encoder
  
      if (par->extradata_size) {
          apng->extra_data = av_mallocz(par->extradata_size + AV_INPUT_BUFFER_PADDING_SIZE);
          if (!apng->extra_data)
              return AVERROR(ENOMEM);
          apng->extra_data_size = par->extradata_size;
          memcpy(apng->extra_data, par->extradata, par->extradata_size);
      }
  
      return 0;
  }
  
  static int flush_packet(AVFormatContext *format_context, AVPacket *packet)
  {
      APNGMuxContext *apng = format_context->priv_data;
      AVIOContext *io_context = format_context->pb;
      AVStream *codec_stream = format_context->streams[0];
      uint8_t *side_data = NULL;
      int side_data_size = 0;
  
      av_assert0(apng->prev_packet);
  
      side_data = av_packet_get_side_data(apng->prev_packet, AV_PKT_DATA_NEW_EXTRADATA, &side_data_size);
  
      if (side_data_size) {
          av_freep(&apng->extra_data);
          apng->extra_data = av_mallocz(side_data_size + AV_INPUT_BUFFER_PADDING_SIZE);
          if (!apng->extra_data)
              return AVERROR(ENOMEM);
          apng->extra_data_size = side_data_size;
          memcpy(apng->extra_data, side_data, apng->extra_data_size);
      }
  
      if (apng->frame_number == 0 && !packet) {
          uint8_t *existing_acTL_chunk;
          uint8_t *existing_fcTL_chunk;
  
          av_log(format_context, AV_LOG_INFO, "Only a single frame so saving as a normal PNG.\n");
  
          // Write normal PNG headers without acTL chunk
          existing_acTL_chunk = apng_find_chunk(MKBETAG('a', 'c', 'T', 'L'), apng->extra_data, apng->extra_data_size);
          if (existing_acTL_chunk) {
              uint8_t *chunk_after_acTL = existing_acTL_chunk + AV_RB32(existing_acTL_chunk) + 12;
              avio_write(io_context, apng->extra_data, existing_acTL_chunk - apng->extra_data);
              avio_write(io_context, chunk_after_acTL, apng->extra_data + apng->extra_data_size - chunk_after_acTL);
          } else {
              avio_write(io_context, apng->extra_data, apng->extra_data_size);
          }
  
          // Write frame data without fcTL chunk
          existing_fcTL_chunk = apng_find_chunk(MKBETAG('f', 'c', 'T', 'L'), apng->prev_packet->data, apng->prev_packet->size);
          if (existing_fcTL_chunk) {
              uint8_t *chunk_after_fcTL = existing_fcTL_chunk + AV_RB32(existing_fcTL_chunk) + 12;
              avio_write(io_context, apng->prev_packet->data, existing_fcTL_chunk - apng->prev_packet->data);
              avio_write(io_context, chunk_after_fcTL, apng->prev_packet->data + apng->prev_packet->size - chunk_after_fcTL);
          } else {
              avio_write(io_context, apng->prev_packet->data, apng->prev_packet->size);
          }
      } else {
          uint8_t *existing_fcTL_chunk;
  
          if (apng->frame_number == 0) {
              uint8_t *existing_acTL_chunk;
  
              // Write normal PNG headers
              avio_write(io_context, apng->extra_data, apng->extra_data_size);
  
              existing_acTL_chunk = apng_find_chunk(MKBETAG('a', 'c', 'T', 'L'), apng->extra_data, apng->extra_data_size);
              if (!existing_acTL_chunk) {
                  uint8_t buf[8];
                  // Write animation control header
                  apng->acTL_offset = avio_tell(io_context);
                  AV_WB32(buf, UINT_MAX); // number of frames (filled in later)
                  AV_WB32(buf + 4, apng->plays);
                  apng_write_chunk(io_context, MKBETAG('a', 'c', 'T', 'L'), buf, 8);
              }
          }
  
          existing_fcTL_chunk = apng_find_chunk(MKBETAG('f', 'c', 'T', 'L'), apng->prev_packet->data, apng->prev_packet->size);
          if (existing_fcTL_chunk) {
              AVRational delay;
  
              existing_fcTL_chunk += 8;
              delay.num = AV_RB16(existing_fcTL_chunk + 20);
              delay.den = AV_RB16(existing_fcTL_chunk + 22);
  
              if (delay.num == 0 && delay.den == 0) {
                  if (packet) {
                      int64_t delay_num_raw = (packet->dts - apng->prev_packet->dts) * codec_stream->time_base.num;
                      int64_t delay_den_raw = codec_stream->time_base.den;
                      if (!av_reduce(&delay.num, &delay.den, delay_num_raw, delay_den_raw, USHRT_MAX) &&
                          !apng->framerate_warned) {
                          av_log(format_context, AV_LOG_WARNING,
                                 "Frame rate is too high or specified too precisely. Unable to copy losslessly.\n");
                          apng->framerate_warned = 1;
                      }
                  } else if (apng->last_delay.num > 0) {
                      delay = apng->last_delay;
                  } else {
                      delay = apng->prev_delay;
                  }
  
                  // Update frame control header with new delay
                  AV_WB16(existing_fcTL_chunk + 20, delay.num);
                  AV_WB16(existing_fcTL_chunk + 22, delay.den);
                  AV_WB32(existing_fcTL_chunk + 26, ~av_crc(av_crc_get_table(AV_CRC_32_IEEE_LE), ~0U, existing_fcTL_chunk - 4, 26 + 4));
              }
              apng->prev_delay = delay;
          }
  
          // Write frame data
          avio_write(io_context, apng->prev_packet->data, apng->prev_packet->size);
      }
      ++apng->frame_number;
  
      av_packet_unref(apng->prev_packet);
      if (packet)
          av_copy_packet(apng->prev_packet, packet);
      return 0;
  }
  
  static int apng_write_packet(AVFormatContext *format_context, AVPacket *packet)
  {
      APNGMuxContext *apng = format_context->priv_data;
      int ret;
  
      if (!apng->prev_packet) {
          apng->prev_packet = av_malloc(sizeof(*apng->prev_packet));
          if (!apng->prev_packet)
              return AVERROR(ENOMEM);
  
          av_copy_packet(apng->prev_packet, packet);
      } else {
          ret = flush_packet(format_context, packet);
          if (ret < 0)
              return ret;
      }
  
      return 0;
  }
  
  static int apng_write_trailer(AVFormatContext *format_context)
  {
      APNGMuxContext *apng = format_context->priv_data;
      AVIOContext *io_context = format_context->pb;
      uint8_t buf[8];
      int ret;
  
      if (apng->prev_packet) {
          ret = flush_packet(format_context, NULL);
          av_freep(&apng->prev_packet);
          if (ret < 0)
              return ret;
      }
  
      apng_write_chunk(io_context, MKBETAG('I', 'E', 'N', 'D'), NULL, 0);
  
      if (apng->acTL_offset && io_context->seekable) {
          avio_seek(io_context, apng->acTL_offset, SEEK_SET);
  
          AV_WB32(buf, apng->frame_number);
          AV_WB32(buf + 4, apng->plays);
          apng_write_chunk(io_context, MKBETAG('a', 'c', 'T', 'L'), buf, 8);
      }
  
      av_freep(&apng->extra_data);
      apng->extra_data = 0;
  
      return 0;
  }
  
  #define OFFSET(x) offsetof(APNGMuxContext, x)
  #define ENC AV_OPT_FLAG_ENCODING_PARAM
  static const AVOption options[] = {
      { "plays", "Number of times to play the output: 0 - infinite loop, 1 - no loop", OFFSET(plays),
        AV_OPT_TYPE_INT, { .i64 = 1 }, 0, UINT_MAX, ENC },
      { "final_delay", "Force delay after the last frame", OFFSET(last_delay),
        AV_OPT_TYPE_RATIONAL, { .dbl = 0 }, 0, USHRT_MAX, ENC },
      { NULL },
  };
  
  static const AVClass apng_muxer_class = {
      .class_name = "APNG muxer",
      .item_name  = av_default_item_name,
      .version    = LIBAVUTIL_VERSION_INT,
      .option     = options,
  };
  
  AVOutputFormat ff_apng_muxer = {
      .name           = "apng",
      .long_name      = NULL_IF_CONFIG_SMALL("Animated Portable Network Graphics"),
      .mime_type      = "image/png",
      .extensions     = "apng",
      .priv_data_size = sizeof(APNGMuxContext),
      .audio_codec    = AV_CODEC_ID_NONE,
      .video_codec    = AV_CODEC_ID_APNG,
      .write_header   = apng_write_header,
      .write_packet   = apng_write_packet,
      .write_trailer  = apng_write_trailer,
      .priv_class     = &apng_muxer_class,
      .flags          = AVFMT_VARIABLE_FPS,
  };
  