# Data flow — ytdl-org/youtube-dl

> Canonical page: https://codevetter.com/unpack/youtube-dl/data-flow

# Data flow — ytdl-org/youtube-dl

Scanned commit 956b8c585591b401a543e409accb163eeaaa1193 (2025-11-26). Generated by codevetter codevetter 1.12.0 on 2026-09-22.

Data moves in one direction through a well-defined pipeline. Inputs: CLI args + config files + batch files produce a URL list; the params dict is the single source of truth shared by all layers. Extractors turn a URL into an 'info dict' (a documented schema with _type discriminators video/url/url_transparent/playlist); process_ie_result resolves indirection recursively; process_video_result normalizes fields and selects formats; process_info emits sidecar files and invokes a protocol-matched FileDownloader that writes .part files and renames on completion; the postprocessor chain mutates/moves the final file; bookkeeping lands in the download archive, cookie jar, and JSON cache.
- URL input boundary: positional args plus lines from --batch-file (or stdin via '-') are merged into all_urls; bare URLs are decoded with the preferred encoding before reaching the extractor loop. — [youtube_dl/__init__.py#L83-99](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/__init__.py#L83-L99) [youtube_dl/utils.py#L4279](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/utils.py#L4279)
- Configuration input boundary: parseOpts merges /etc/youtube-dl.conf, user config (XDG_CONFIG_HOME/youtube-dl/config, ~/.config/youtube-dl.conf, %APPDATA% variants, ~/youtube-dl.conf), --config-location file, then argv — later entries override earlier ones; --ignore-config skips them. — [youtube_dl/options.py#L42-90](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/options.py#L42-L90) [youtube_dl/options.py#L904-942](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/options.py#L904-L942)
- The info dict is the canonical intermediate representation: extractor/common.py's class docstring specifies mandatory fields (id, title, and url-or-formats) plus ~50 optional fields and the _type discriminator values (video, playlist, multi_video, url, url_transparent, compat_list). — [youtube_dl/extractor/common.py#L98-417](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/extractor/common.py#L98-L417)
- extract_info iterates self._ies calling ie.suitable(url) (compiled _VALID_URL regexes); the first match's extract() runs initialize() (geo-bypass, login) then _real_extract(url); results are stamped with extractor/webpage_url/extractor_key by add_default_extra_info. — [youtube_dl/YoutubeDL.py#L841-878](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/YoutubeDL.py#L841-L878) [youtube_dl/extractor/common.py#L436-463](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/extractor/common.py#L436-L463) [youtube_dl/extractor/common.py#L568-587](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/extractor/common.py#L568-L587) [youtube_dl/YoutubeDL.py#L993-999](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/YoutubeDL.py#L993-L999)
- process_ie_result recursively resolves indirection: 'url'/'url_transparent' results re-enter extract_info (possibly pinned to an ie_key); 'playlist'/'multi_video'/'compat_list' results go to __process_playlist which slices entries, injects playlist_* extra_info, and reprocesses each entry via __process_iterable_entry. — [youtube_dl/YoutubeDL.py#L1001-1107](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/YoutubeDL.py#L1001-L1107) [youtube_dl/YoutubeDL.py#L1108-1223](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/YoutubeDL.py#L1108-L1223)
- process_video_result normalizes a video info dict: forces string/numeric field types, sorts thumbnails, fills common fields, computes requested_subtitles, filters malformed formats, sorts formats with _sort_formats, and runs the parsed format selector (from build_format_selector) to produce formats_to_download or requested_formats for A+V merge. — [youtube_dl/YoutubeDL.py#L1645-1870](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/YoutubeDL.py#L1645-L1870) [youtube_dl/YoutubeDL.py#L1312-1577](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/YoutubeDL.py#L1312-L1577)
- process_info is the output boundary: it computes the filename via prepare_filename, writes .description/.annotations.xml/subtitle/.info.json/thumbnail files first, then calls dl() which instantiates the downloader chosen by get_suitable_downloader and copies http_headers via _calc_headers. — [youtube_dl/YoutubeDL.py#L1952-2095](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/YoutubeDL.py#L1952-L2095) [youtube_dl/downloader/__init__.py#L8-11](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/downloader/__init__.py#L8-L11)
- HttpFD.real_download streams to `filename + '.part'` opened just-in-time via sanitize_open, honoring resume (Range header + Content-Range validation), retry on 5xx/ECONNRESET/timeout, min/max filesize aborts, then try_rename to the final name and try_utime from Last-Modified. — [youtube_dl/downloader/http.py#L27-362](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/downloader/http.py#L27-L362)
- Fragmented downloads (HlsFD, DashSegmentsFD, F4mFD, IsmFD) share FragmentFD, which keeps a `.ytdl` JSON bookkeeping file per incomplete download (extractor/downloader state, current_fragment, fragment_count) enabling resume and consistency checks. — [youtube_dl/downloader/fragment.py#L17-50](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/downloader/fragment.py#L17-L50) [youtube_dl/downloader/hls.py#L24-60](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/downloader/hls.py#L24-L60)
- Postprocessing output boundary: post_process chains info_dict['__postprocessors'] (e.g. FFmpegMergerPP for A+V merge, fixup PPs) before self._pps; each pp.run returns (files_to_delete, info); originals are deleted unless keepvideo. — [youtube_dl/YoutubeDL.py#L2319-2339](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/YoutubeDL.py#L2319-L2339) [youtube_dl/YoutubeDL.py#L2097-2162](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/YoutubeDL.py#L2097-L2162)
- State owners: the cookie jar (YoutubeDLCookieJar, Netscape format, optionally file-backed via --cookies) is owned by YoutubeDL._setup_opener; extractor/player caches (e.g. YouTube 'sigfuncs') live under the Cache section/key namespace; the download archive is a plain text append log. — [youtube_dl/YoutubeDL.py#L2593-2604](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/YoutubeDL.py#L2593-L2604) [youtube_dl/utils.py#L2935-3063](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/utils.py#L2935-L3063) [youtube_dl/cache.py#L55-129](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/cache.py#L55-L129) [youtube_dl/extractor/youtube.py#L1814-1838](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/extractor/youtube.py#L1814-L1838)
- Header/cookie hygiene is enforced at boundaries: FileDownloader.download documents stripping Cookie headers; _remove_cookie_header filters them from http_headers; header-supplied cookies are rescoped per-URL domain by _apply_header_cookies to prevent cross-domain leaks. — [youtube_dl/downloader/common.py#L340-347](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/downloader/common.py#L340-L347) [youtube_dl/YoutubeDL.py#L901-972](https://github.com/ytdl-org/youtube-dl/blob/956b8c585591b401a543e409accb163eeaaa1193/youtube_dl/YoutubeDL.py#L901-L972)

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