av1代码学习7---encode_with_recode_lo

1，函数功能

该函数主要置量化相关的参数和分块信息后进行编码，编码之后会根据打包的码流大小判断是否谁需要重新编码（loop）。

2，代码学习

static int encode_with_recode_loop(AV1_COMP *cpi, size_t *size, uint8_t *dest) {
  AV1_COMMON *const cm = &cpi->common;
  RATE_CONTROL *const rc = &cpi->rc;
  const int allow_recode = (cpi->sf.recode_loop != DISALLOW_RECODE);

  set_size_independent_vars(cpi);

  cpi->source->buf_8bit_valid = 0;

  av1_setup_frame_size(cpi);

  int top_index = 0, bottom_index = 0;
  int q = 0, q_low = 0, q_high = 0;
  set_size_dependent_vars(cpi, &q, &bottom_index, &top_index);
  q_low = bottom_index;
  q_high = top_index;

  // Loop variables
  int loop_count = 0;
  int loop_at_this_size = 0;
  int loop = 0;
  int overshoot_seen = 0;
  int undershoot_seen = 0;
  int low_cr_seen = 0;

#if CONFIG_COLLECT_COMPONENT_TIMING
  printf("\n Encoding a frame:");
#endif
  do {//loop为1的话
    loop = 0;
    aom_clear_system_state();

    // if frame was scaled calculate global_motion_search again if already
    // done
    //帧的缩放做过了的话再次进行全局运动搜索（即全局运动搜索的标志位置0）
    if (loop_count > 0 && cpi->source && cpi->global_motion_search_done) {
      if (cpi->source->y_crop_width != cm->width ||
          cpi->source->y_crop_height != cm->height) {
        cpi->global_motion_search_done = 0;
      }
    }
    //帧缩放
    cpi->source =
        av1_scale_if_required(cm, cpi->unscaled_source, &cpi->scaled_source);
    //前一帧缩放
    if (cpi->unscaled_last_source != NULL) {
      cpi->last_source = av1_scale_if_required(cm, cpi->unscaled_last_source,
                                               &cpi->scaled_last_source);
    }
    //关键帧或者只能帧内编码的时候
    if (!frame_is_intra_only(cm)) {
      if (loop_count > 0) {
        release_scaled_references(cpi);//释放帧间参考帧列表
      }
      scale_references(cpi);//量化参考帧列表
    }
    av1_set_quantizer(cm, q);
    av1_init_quantizer(cpi);

    av1_set_variance_partition_thresholds(cpi, q, 0);

    //printf("Frame %d/%d: q = %d, frame_type = %d superres_denom = %d\n",
    //        cm->current_frame.frame_number, cm->show_frame, q,
    //        cm->current_frame.frame_type, cm->superres_scale_denominator);

    if (loop_count == 0) {
      setup_frame(cpi);
    } else if (get_primary_ref_frame_buf(cm) == NULL) {
      // Base q-index may have changed, so we need to assign proper default coef
      // probs before every iteration.
      av1_default_coef_probs(cm);
      av1_setup_frame_contexts(cm);
    }
    //根据量化建立索引？
    if (cpi->oxcf.aq_mode == VARIANCE_AQ) {
      av1_vaq_frame_setup(cpi);
    } else if (cpi->oxcf.aq_mode == COMPLEXITY_AQ) {
      av1_setup_in_frame_q_adj(cpi);
    } else if (cpi->oxcf.aq_mode == CYCLIC_REFRESH_AQ && !allow_recode) {
      suppress_active_map(cpi);
      av1_cyclic_refresh_setup(cpi);
      apply_active_map(cpi);
    }

    if (cm->seg.enabled) {//如果分块的话
      if (!cm->seg.update_data && cm->prev_frame) {//前一帧存在并且划分未更新
        segfeatures_copy(&cm->seg, &cm->prev_frame->seg);//复制前一帧的划分给cm-seg
      } else {
        av1_calculate_segdata(&cm->seg);//前一帧不存在则计算当前的&cm->seg
      }
    } else {//不进行划分则直接申请cm->seg的空间
      memset(&cm->seg, 0, sizeof(cm->seg));
    }
    segfeatures_copy(&cm->cur_frame->seg, &cm->seg);//将cm->seg赋予当前帧的划分

    if (allow_recode) save_coding_context(cpi);
#if CONFIG_COLLECT_COMPONENT_TIMING
    start_timing(cpi, av1_encode_frame_time);
#endif
    // transform / motion compensation build reconstruction frame
    av1_encode_frame(cpi);//编码
#if CONFIG_COLLECT_COMPONENT_TIMING
    end_timing(cpi, av1_encode_frame_time);
#endif

    aom_clear_system_state();

    // Dummy pack of the bitstream using up to date stats to get an
    // accurate estimate of output frame size to determine if we need
    // to recode.，根据已经编码好的码流大小判断是否进行重新编码
    if (cpi->sf.recode_loop >= ALLOW_RECODE_KFARFGF) {
      restore_coding_context(cpi);

      finalize_encoded_frame(cpi);
      int largest_tile_id = 0;  // Output from bitstream: unused here
      if (av1_pack_bitstream(cpi, dest, size, &largest_tile_id) != AOM_CODEC_OK)
        return AOM_CODEC_ERROR;

      rc->projected_frame_size = (int)(*size) << 3;
      restore_coding_context(cpi);
    }
    //重新编码
    if (allow_recode) {
      // Update q and decide whether to do a recode loop
      recode_loop_update_q(cpi, &loop, &q, &q_low, &q_high, top_index,
                           bottom_index, &undershoot_seen, &overshoot_seen,
                           &low_cr_seen, loop_at_this_size);
    }

    // Special case for overlay frame.
    if (rc->is_src_frame_alt_ref &&
        rc->projected_frame_size < rc->max_frame_bandwidth)
      loop = 0;

    if (allow_recode && !cpi->sf.gm_disable_recode &&
        recode_loop_test_global_motion(cpi)) {
      loop = 1;
    }

    if (cpi->tpl_model_pass == 1) {
      assert(cpi->oxcf.enable_tpl_model == 2);
      av1_tpl_setup_forward_stats(cpi);
      cpi->tpl_model_pass = 0;
      loop = 1;
    }

    if (loop) {
      ++loop_count;
      ++loop_at_this_size;

#if CONFIG_INTERNAL_STATS
      ++cpi->tot_recode_hits;
#endif
    }
#if CONFIG_COLLECT_COMPONENT_TIMING
    if (loop) printf("\n Recoding:");
#endif
  } while (loop);

  return AOM_CODEC_OK;
}