SELECT 
  cv.video_id, 
  cvd.video, 
  cvd.description, 
  cvd.short_description, 
  cvd.like_count, 
  cvd.comment_count, 
  cvd.youtube_id, 
  cv.status, 
  cv.user_id, 
  cv.community_thumbnail, 
  cv.community_video_url, 
  cv.community_url, 
  cu.firstname, 
  CASE WHEN MAX(mum.avatar) IS NOT NULL 
  AND MAX(mum.avatar) != '' THEN CONCAT(
    'https://cdn.kindlife.in/', 
    MAX(mum.avatar)
  ) ELSE 'https://cdn.kindlife.in/images/ui_icon/user-default.svg' END AS userAvatar 
FROM 
  cscart_cp_videos cv 
  LEFT JOIN cscart_cp_video_descriptions cvd ON cvd.video_id = cv.video_id 
  AND cvd.lang_code = 'en' 
  LEFT JOIN cscart_users cu ON cu.user_id = cv.user_id 
  LEFT JOIN kl_user_pref_master mum ON cv.user_id = mum.user_id 
WHERE 
  1 
  AND cv.user_id = 21551 
  AND cv.status = 'A' 
GROUP BY 
  cv.video_id, 
  cvd.video, 
  cvd.description, 
  cvd.short_description, 
  cvd.like_count, 
  cvd.comment_count, 
  cv.status, 
  cv.user_id, 
  cv.community_thumbnail, 
  cv.community_video_url, 
  cu.firstname 
ORDER BY 
  cv.timestamp DESC 
LIMIT 
  340, 10

Query time 0.00787

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "338.37"
    },
    "ordering_operation": {
      "using_filesort": true,
      "grouping_operation": {
        "using_temporary_table": true,
        "using_filesort": false,
        "nested_loop": [
          {
            "table": {
              "table_name": "cv",
              "access_type": "ref",
              "possible_keys": [
                "status_idx",
                "user_id_idx",
                "idx_cp_videos_status_userid_videoid",
                "idx_status_timestamp"
              ],
              "key": "idx_cp_videos_status_userid_videoid",
              "used_key_parts": [
                "status",
                "user_id"
              ],
              "key_length": "7",
              "ref": [
                "const",
                "const"
              ],
              "rows_examined_per_scan": 457,
              "rows_produced_per_join": 457,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "39.35",
                "eval_cost": "45.70",
                "prefix_cost": "85.05",
                "data_read_per_join": "714K"
              },
              "used_columns": [
                "video_id",
                "timestamp",
                "status",
                "user_id",
                "community_url",
                "community_thumbnail",
                "community_video_url"
              ]
            }
          },
          {
            "table": {
              "table_name": "cvd",
              "access_type": "eq_ref",
              "possible_keys": [
                "PRIMARY"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "video_id",
                "lang_code"
              ],
              "key_length": "9",
              "ref": [
                "cscart_db.cv.video_id",
                "const"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 457,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "114.25",
                "eval_cost": "45.70",
                "prefix_cost": "245.00",
                "data_read_per_join": "1M"
              },
              "used_columns": [
                "video_id",
                "lang_code",
                "youtube_id",
                "video",
                "description",
                "short_description",
                "like_count",
                "comment_count"
              ]
            }
          },
          {
            "table": {
              "table_name": "cu",
              "access_type": "const",
              "possible_keys": [
                "PRIMARY"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "user_id"
              ],
              "key_length": "3",
              "ref": [
                "const"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 457,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "0.98",
                "eval_cost": "45.70",
                "prefix_cost": "291.68",
                "data_read_per_join": "3M"
              },
              "used_columns": [
                "user_id",
                "firstname"
              ]
            }
          },
          {
            "table": {
              "table_name": "mum",
              "access_type": "const",
              "possible_keys": [
                "PRIMARY"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "user_id"
              ],
              "key_length": "3",
              "ref": [
                "const"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 457,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "0.99",
                "eval_cost": "45.70",
                "prefix_cost": "338.37",
                "data_read_per_join": "8M"
              },
              "used_columns": [
                "user_id",
                "avatar"
              ]
            }
          }
        ]
      }
    }
  }
}