Youtube plugin add start at option (#3604)

* add start_at option to youtube plugin

* add test for youtube start_at directive option

* add youtube start_at option to CHANGES.txt

* update youtube directive docs to include start_at option

* fix lint error

CHANGES.txt

@@ -5,6 +5,7 @@ Features
 --------
 
 * Gallery index pages support the `status` flag (Issue #3598)
+* Add ``start_at`` option to youtube directive (Issue #3603)
 
 
 New in v8.2.0

docs/manual.rst

@@ -2622,13 +2622,14 @@ Once you have that, all you need to do is:
 
     .. youtube:: 8N_tupPBtWQ
 
-Supported options: ``height``, ``width``, ``align`` (one of ``left``,
+Supported options: ``height``, ``width``, ``start_at``, ``align`` (one of ``left``,
 ``center``, ``right``) — all are optional. Example:
 
 .. code:: restructuredtext
 
     .. youtube:: 8N_tupPBtWQ
        :align: center
+       :start_at: 4
 
 Vimeo
 ~~~~~

nikola/plugins/compile/rest/youtube.py

@@ -48,7 +48,7 @@ def set_site(self, site):
 CODE = """\
 <div class="youtube-video{align}">
 <iframe width="{width}" height="{height}"
-src="https://www.youtube-nocookie.com/embed/{yid}?rel=0&wmode=transparent"
+src="https://www.youtube-nocookie.com/embed/{yid}?rel=0&wmode=transparent{start_at}"
 frameborder="0" allow="encrypted-media" allowfullscreen
 ></iframe>
 </div>"""
@@ -69,7 +69,8 @@ class Youtube(Directive):
     option_spec = {
         "width": directives.unchanged,
         "height": directives.unchanged,
-        "align": _align_choice
+        "align": _align_choice,
+        "start_at": directives.unchanged
     }
 
     def run(self):
@@ -85,6 +86,14 @@ def run(self):
             options['align'] = ' align-' + self.options['align']
         else:
             options['align'] = ''
+
+        start_at = options.get('start_at')
+
+        if start_at:
+            options['start_at'] = '&start=' + start_at
+        else:
+            options['start_at'] = ''
+
         return [nodes.raw('', CODE.format(**options), format='html')]
 
     def check_content(self):

tests/test_rst_compiler.py

@@ -87,6 +87,29 @@ def test_youtube_iframe():
     )
 
 
+def test_youtube_iframe_start_at():
+    """Test Youtube iframe tag generation with start_at attribute"""
+
+    sample = ".. youtube:: YID\n   :height: 400\n   :width: 600\n   :start_at: 60"
+    html = get_html_from_rst(sample)
+    assert_html_contains(
+        html,
+        "iframe",
+        attributes={
+            "src": (
+                "https://www.youtube-nocookie.com"
+                "/embed/YID?rel=0&"
+                "wmode=transparent&start=60"
+            ),
+            "height": "400",
+            "width": "600",
+            "frameborder": "0",
+            "allowfullscreen": "",
+            "allow": "encrypted-media",
+        },
+    )
+
+
 def test_vimeo(disable_vimeo_api_query):
     """Test Vimeo iframe tag generation"""