[BiliBili] --flat-playlist does not work

[dban0001]

Make sure you are using the latest version: run youtube-dl --version and ensure your version is 2018.03.20. If it's not, read this FAQ entry and update. Issues with outdated version will be rejected.

• I've verified and I assure that I'm running youtube-dl 2018.03.20

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• At least skimmed through the README, most notably the FAQ and BUGS sections
• Searched the bugtracker for similar issues including closed ones
• Checked that provided video/audio/playlist URLs (if any) are alive and playable in a browser

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• Bug report (encountered problems with youtube-dl)
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• Question
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python -m youtube_dl "https://www.bilibili.com/video/av20631514/" --dump-single-json --flat-playlist -v    
[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'https://www.bilibili.com/video/av20631514/', u'--dump-single-json', u'--flat-playlist', u'-v']
[debug] Encodings: locale UTF-8, fs UTF-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2018.03.20
[debug] Git HEAD: a66d1d0
[debug] Python version 2.7.12 (CPython) - Linux-4.8.0-58-generic-x86_64-with-LinuxMint-18.1-serena
[debug] exe versions: ffmpeg N-86486-g752dd19, ffprobe N-86486-g752dd19, phantomjs 2.1.1
[debug] Proxy map: {}
[debug] Default format spec: bestvideo+bestaudio/best
[debug] Default format spec: bestvideo+bestaudio/best
[debug] Default format spec: bestvideo+bestaudio/best
[debug] Default format spec: bestvideo+bestaudio/best

I used --flat-playlist with --dump-single-json and I expected the entries array to contain

{
  "_type": "url",
  "url": "https://www.bilibili.com/video/av20631514/"
}

objects, but they actually contain the final url. Is this just how the bilibili site works or does youtube-dl ignore the --flat-playlist flag for this extractor?

{
  "extractor": "BiliBili",
  "_type": "multi_video",
  "description": "网络三位食物设定的idol",
  "title": "有吉反省会 180310",
  "extractor_key": "BiliBili",
  "webpage_url": "https://www.bilibili.com/video/av20631514/",
  "entries": [
    {
      "extractor": "BiliBili",
      "protocol": "http",
      "upload_date": "20180311",
      "duration": 1494.237,
      "playlist_index": 1,
      "playlist": "有吉反省会 180310",
      "title": "有吉反省会 180310",
      "id": "20631514_part1",
      "playlist_id": "20631514",
      "filesize": 35271693,
      "requested_subtitles": null,
      "thumbnail": "http://i0.hdslb.com/bfs/archive/e2956e8f2651c4025086ca27b0736d98e911a4b8.png",
      "webpage_url_basename": "av20631514",
      "display_id": "20631514_part1",
      "description": "网络三位食物设定的idol",
      "format": "1 - unknown",
      "timestamp": 1520773631,
      "playlist_uploader": null,
      "uploader": "qu0411",
      "format_id": "1",
      "uploader_id": "9120150",
      "playlist_title": "有吉反省会 180310",
      "thumbnails": [
        {
          "url": "http://i0.hdslb.com/bfs/archive/e2956e8f2651c4025086ca27b0736d98e911a4b8.png",
          "id": "0"
        }
      ],
      "url": "http://upos-hz-mirrorcos.acgvideo.com/upgcxcode/62/82/33758262/33758262-1-32.flv?um_deadline=1521505505&platform=pc&rate=181448&oi=1339450470&um_sign=f1bae2bf5e02b1cea1bcfda3b5364d88&gen=playurl&os=cos",
      "extractor_key": "BiliBili",
      "http_headers": {
        "Accept-Language": "en-us,en;q=0.5",
        "Accept-Encoding": "gzip, deflate",
        "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8",
        "User-Agent": "Mozilla/5.0 (X11; Linux x86_64; rv:59.0) Gecko/20100101 Firefox/59.0 (Chrome)",
        "Accept-Charset": "ISO-8859-1,utf-8;q=0.7,*;q=0.7",
        "Referer": "https://www.bilibili.com/video/av20631514/"
      },
      "ext": "flv",
      "webpage_url": "https://www.bilibili.com/video/av20631514/",
      "formats": [
        {
          "protocol": "http",
          "format": "0 - unknown",
          "url": "http://ws.acgvideo.com/a/20/33758262-1-32.flv?wsTime=1521505505&platform=pc&wsSecret2=fcc7ca85729b899e5ec57f7fa1bc1f64&oi=1339450470&rate=154",
          "http_headers": {
            "Accept-Charset": "ISO-8859-1,utf-8;q=0.7,*;q=0.7",
            "Accept-Language": "en-us,en;q=0.5",
            "Accept-Encoding": "gzip, deflate",
            "Referer": "https://www.bilibili.com/video/av20631514/",
            "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8",
            "User-Agent": "Mozilla/5.0 (X11; Linux x86_64; rv:59.0) Gecko/20100101 Firefox/59.0 (Chrome)"
          },
          "ext": "flv",
          "preference": -3,
          "format_id": "0"
        },
        {
          "protocol": "http",
          "format": "1 - unknown",
          "url": "http://upos-hz-mirrorcos.acgvideo.com/upgcxcode/62/82/33758262/33758262-1-32.flv?um_deadline=1521505505&platform=pc&rate=181448&oi=1339450470&um_sign=f1bae2bf5e02b1cea1bcfda3b5364d88&gen=playurl&os=cos",
          "http_headers": {
            "Accept-Charset": "ISO-8859-1,utf-8;q=0.7,*;q=0.7",
            "Accept-Language": "en-us,en;q=0.5",
            "Accept-Encoding": "gzip, deflate",
            "Referer": "https://www.bilibili.com/video/av20631514/",
            "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8",
            "User-Agent": "Mozilla/5.0 (X11; Linux x86_64; rv:59.0) Gecko/20100101 Firefox/59.0 (Chrome)"
          },
          "ext": "flv",
          "filesize": 35271693,
          "format_id": "1"
        }
      ],
      "playlist_uploader_id": null,
      "n_entries": 4
    }
    // removed 3 other entries
  ],
  "id": "20631514",
  "webpage_url_basename": "av20631514"
}

[dstftw]

https://www.bilibili.com/video/av20631514/ is not a playlist.