Imported from damionrashford/media-os (.claude/skills/gstreamer-docs/SKILL.md). Install upstream with npx skills add damionrashford/media-os --skill gstreamer-docs. Copyright stays with the author.

GStreamer Docs

Context: $ARGUMENTS

Quick start

• Find an element / property / signal: -> Step 2 (search --query <term>)
• Read the full docs for one element: -> Step 3 (element --name <name>)
• Read one section by anchor: -> Step 4 (section --page <page> --id <anchor>)
• Grab a whole page: -> Step 5 (fetch --page <name>)
• Prime cache for offline use: -> Step 6 (index)

When to use

• User asks "what does element X do?" or "what properties does webrtcbin expose?"
• Need to verify an element name, property, pad, or signal exists before recommending it.
• Need the canonical gstreamer.freedesktop.org URL to cite in a response.
• Before writing any non-trivial gst-launch-1.0 pipeline, verify the element and its caps/properties.
• Need to know which plugin package an element ships in.

Step 1 — Know the page catalog

The script targets a fixed list of plugin-index pages + top-level guides. Get the list:

uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py list-pages

Common picks:

Read references/pages.md for the full catalog.

Step 2 — Search first (this is the default)

When the user names an element, property, pad, or signal, search across all pages:

uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py search --query "webrtcbin" --limit 5

Scope to a page when you know it (faster, less noise):

uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py search --query "animation-mode" --page videotestsrc

Output per hit:

--- <page>:<line> — <nearest heading>
<canonical URL with anchor>
<snippet with ±3 lines of context>

--format json for machine-parseable output; --regex for anchored patterns.

Step 3 — Read one element's docs

When you know the element name (e.g. filesrc, playbin3, webrtcbin):

uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py element --name filesrc
uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py element --name webrtcbin --format json

The script resolves element pages automatically across the two URL shapes GStreamer uses:

• Multi-element plugin: /<plugin>/<element>.html (e.g. /coreelements/filesrc.html, /playback/playbin3.html, /rtsp/rtspsrc.html, /hls/hlssink2.html, /srt/srtsrc.html, /rswebrtc/webrtcsink.html).
• Singleton plugin: /<element>/index.html (e.g. /videotestsrc/index.html, /audiotestsrc/index.html, /webrtclib/index.html, /x264/index.html).

You can also debug which shape was picked:

uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py resolve --element webrtcbin

Step 4 — Read one section

When a search hit shows an anchor like [§videotestsrc:animation-mode] and you want the whole block:

uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py section --page videotestsrc --id "videotestsrc:animation-mode"
uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py section --element webrtcbin --id ice-agent

--id accepts a raw anchor id or a heading keyword (case-insensitive substring match on the first matching heading).

Step 5 — Fetch a whole page

Rare — usually overkill. When you need it:

uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py fetch --page coreelements
uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py fetch --element playbin3 --format json

Step 6 — Prime cache (optional)

uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py index

Downloads every known landing page into ~/.cache/gstreamer-docs/ with a 0.3s delay.

Override the cache directory with export GSTREAMER_DOCS_CACHE=/path/to/dir. Clear: gstdocs.py clear-cache.

Gotchas

• Bare /<element>.html is universally 404. Elements live under a plugin dir — /coreelements/filesrc.html, not /filesrc.html. The element subcommand handles this for you; never construct the URL yourself.
• Two element-page shapes exist. Multi-element plugin: /<plugin>/<element>.html. Singleton plugin: /<element>/index.html. resolve --element tells you which shape was picked.
• Anchor syntax is Hotdoc-specific. You'll see three flavours inside page text: #<element> (the element landing block), #<element>:<property> with a literal colon (e.g. #videotestsrc:animation-mode), and #Gst<CamelCase>!<pad> (e.g. #GstVideoTestSrc!src for the src pad). Pass the form you see in search output verbatim to section --id.
• webrtcbin vs webrtcsink are distinct. webrtcbin is the low-level C element in plugin webrtc — you handle SDP + ICE yourself. webrtcsink / webrtcsrc are the high-level Rust elements in plugin rswebrtc that speak WHIP/WHEP and negotiate automatically. Don't mix their properties.
• playbin vs playbin3. playbin is the legacy high-level player. playbin3 is the current one — different signals, different bus messages, different stream-selection API. Check which one you're actually using.
• decodebin3 / urisourcebin stream-selection is different from decodebin/uridecodebin. Events are GST_EVENT_SELECT_STREAMS + GST_MESSAGE_STREAM_COLLECTION rather than the old autoplug-* signals. Don't port old code verbatim.
• gst-inspect-1.0 <element> is authoritative for local builds. If the online docs don't match what your installed GStreamer exposes, the CLI is right — some plugins are rolled from different upstreams (gst-plugins-good vs bad vs ugly vs rs) and versions diverge.
• Docs are Hotdoc-generated, NOT Sphinx. Don't assume Sphinx conventions like :py:class: or _CPPv4N... — GStreamer anchors are flatter (element, element:property, GstType!pad).
• Plugin packages: good/bad/ugly/base/rs. "bad" means "not yet up to par", NOT "buggy". Many widely-used elements (webrtcbin, hlssink2, srtsink) live in gst-plugins-bad or gst-plugins-rs. If gst-inspect-1.0 foo comes up empty, you probably haven't installed the plugin-set it ships in.
• Rust plugins (gst-plugins-rs) ship separately. webrtcsink, awstranscriber, fallbackswitch, etc. are Rust — check rswebrtc and related index pages, not the C plugin pages.
• Search may miss content in complex tables. The text extractor flattens multi-column property tables. If a search hit looks incomplete, open the canonical URL printed in the hit header.
• Cache never expires automatically. After a GStreamer release reshuffles plugins, run clear-cache + index.
• The script is stdlib-only — no pip install. Works anywhere Python 3.9+ runs.

Examples

Example 1 — "What properties does webrtcbin expose?"

uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py element --name webrtcbin

Or search + jump:

uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py search --query "webrtcbin" --page webrtc --limit 5
uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py section --element webrtcbin --id "webrtcbin:stun-server"

Example 2 — "Does hlssink2 support fMP4 / CMAF?"

uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py search --query "hlssink2" --page hls
uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py element --name hlssink2

Example 3 — "What's the gst-launch-1.0 syntax for named elements and caps filters?"

uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py search --query "pipeline description" --page gst-launch

Example 4 — "What does videotestsrc animation-mode=frames actually do?"

uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py section --page videotestsrc --id "videotestsrc:animation-mode"

Example 5 — "Which plugin provides rtspclientsink?"

uv run ${CLAUDE_SKILL_DIR}/scripts/gstdocs.py resolve --element rtspclientsink

(Prints URL + shape. URL's first path segment is the plugin.)

Troubleshooting

Error: unknown page: foo

Cause: The name isn't in the catalog. Solution: Run list-pages. Common mistakes: using elements instead of coreelements; rtspsrc (an element) instead of rtsp (the plugin).

Error: could not resolve element <name>

Cause: The element isn't in ELEMENT_HINTS, the singleton-plugin guess failed, and no known plugin landing page linked to it. Solution: Run gst-inspect-1.0 <name> to confirm the element exists and see its plugin. Then search --query "<name>" across the whole catalog to find the right plugin page. If it's a Rust plugin not in our list yet, the element lives at /<plugin>/<name>.html under gst-plugins-rs — fetch the URL directly with urllib until the catalog is updated.

Error: urlopen error [SSL: CERTIFICATE_VERIFY_FAILED]

Cause: System certificate store is out of date (usually macOS Python). Solution: Run /Applications/Python\ 3.x/Install\ Certificates.command, or set SSL_CERT_FILE to a valid CA bundle. Do NOT disable SSL verification.

Search returns zero hits

Cause: The term isn't on the pages you queried. Solution: Drop --page to search everything; try a broader query. Some APIs are in the base-class pages (base, gstreamer) rather than the element page.

Anchor not found with section --id

Cause: Hotdoc anchors include colons and ! which copy-paste fine but may confuse shells. Quote them. Solution: --id "videotestsrc:animation-mode" with quotes, or fall back to a heading keyword: --id animation-mode.

Cache is stale after GStreamer upstream release

Solution: gstdocs.py clear-cache then gstdocs.py index.

Reference docs

• Full page catalog with element-to-plugin hints and anchor-syntax details -> references/pages.md