If no transcript is provided, search for a consistent transcript

tests/unit/via/views/view_video_test.py

@@ -6,7 +6,7 @@
 from pyramid.httpexceptions import HTTPUnauthorized
 
 from via.exceptions import BadURL
-from via.views.view_video import view_youtube_video
+from via.views.view_video import CAPTION_TRACK_PREFERENCES, view_youtube_video
 
 # webargs's kwargs injection into view functions falsely triggers Pylint's
 # no-value-for-parameter all the time so just disable it file-wide.
@@ -22,7 +22,6 @@ def test_it(
         video_url,
         ViaSecurityPolicy,
     ):
-        # Override default `None` response.
         pyramid_request.params["via.video.lang"] = sentinel.transcript_id
 
         response = view_youtube_video(pyramid_request)
@@ -61,11 +60,38 @@ def test_it(
             },
         }
 
-    def test_it_defaults_to_en(self, pyramid_request, youtube_service):
+    def test_it_looks_up_transcripts(self, pyramid_request, youtube_service):
         pyramid_request.params.pop("via.video.lang", None)
 
         response = view_youtube_video(pyramid_request)
 
+        youtube_service.get_video_info.assert_called_once_with(
+            video_url=youtube_service.canonical_video_url.return_value
+        )
+        video = youtube_service.get_video_info.return_value
+        video.caption.find_matching_track.assert_called_once_with(
+            CAPTION_TRACK_PREFERENCES
+        )
+        caption_track = video.caption.find_matching_track.return_value
+
+        assert response["api"]["transcript"]["url"] == pyramid_request.route_url(
+            "api.youtube.transcript",
+            video_id=youtube_service.get_video_id.return_value,
+            transcript_id=caption_track.id,
+        )
+
+    @pytest.mark.parametrize("has_captions,has_matches", ((True, False), (False, True)))
+    def test_it_defaults_to_en_a(
+        self, pyramid_request, youtube_service, has_captions, has_matches
+    ):
+        pyramid_request.params.pop("via.video.lang", None)
+        video = youtube_service.get_video_info.return_value
+        video.has_captions = has_captions
+        if not has_matches:
+            video.caption.find_matching_track.return_value = None
+
+        response = view_youtube_video(pyramid_request)
+
         assert response["api"]["transcript"]["url"] == pyramid_request.route_url(
             "api.youtube.transcript",
             video_id=youtube_service.get_video_id.return_value,
@@ -82,7 +108,7 @@ def test_it_errors_if_the_url_is_invalid(self, pyramid_request):
             "query": {"url": ["Not a valid URL."]}
         }
 
-    def test_it_errors_if_the_url_is_not_a_YouTube_url(
+    def test_it_errors_if_the_url_is_not_a_youtube_url(
         self, pyramid_request, youtube_service
     ):
         # YouTubeService returns None if it can't extract the YouTube video ID

via/views/view_video.py

@@ -1,4 +1,5 @@
 import marshmallow
+from h_matchers import Any
 from h_vialib import Configuration
 from pyramid.httpexceptions import HTTPUnauthorized
 from pyramid.view import view_config
@@ -8,25 +9,43 @@
 from via.exceptions import BadURL
 from via.security import ViaSecurityPolicy
 from via.services import YouTubeService
+from via.services.youtube_api import CaptionTrack
+
+CAPTION_TRACK_PREFERENCES = (
+    # Plain English first
+    CaptionTrack(language_code="en"),
+    # Plain varieties of English
+    CaptionTrack(language_code=Any.string.matching("^en-.*")),
+    # Sub-categories of plain English
+    CaptionTrack(language_code="en", name=Any()),
+    # English varieties with names
+    CaptionTrack(language_code=Any.string.matching("^en-.*"), name=Any()),
+    # Any auto generated English
+    CaptionTrack(language_code=Any.string.matching("^en-.*"), name=Any(), kind=Any()),
+    # Any track which can be translated into English
+    CaptionTrack(
+        language_code=Any(), name=Any(), kind=Any(), translated_language_code="en"
+    ),
+)
 
 
 @view_config(renderer="via:templates/view_video.html.jinja2", route_name="youtube")
 @use_kwargs(
     {"url": fields.Url(required=True)}, location="query", unknown=marshmallow.INCLUDE
 )
 def view_youtube_video(request, url, **kwargs):
-    youtube_service = request.find_service(YouTubeService)
+    youtube_service: YouTubeService = request.find_service(YouTubeService)
 
     if not youtube_service.enabled:
         raise HTTPUnauthorized()
 
     video_id = youtube_service.get_video_id(url)
-    video_url = youtube_service.canonical_video_url(video_id)
-    video_title = youtube_service.get_video_title(video_id)
-
     if not video_id:
         raise BadURL(f"Unsupported video URL: {url}", url=url)
 
+    video_url = youtube_service.canonical_video_url(video_id)
+    video_title = youtube_service.get_video_title(video_id)
+
     via_config, client_config = Configuration.extract_from_params(kwargs)
 
     return {
@@ -41,7 +60,9 @@ def view_youtube_video(request, url, **kwargs):
                 "url": request.route_url(
                     "api.youtube.transcript",
                     video_id=video_id,
-                    transcript_id=via_config.get("video", {}).get("lang", "en.a"),
+                    transcript_id=_get_transcript_id(
+                        youtube_service, video_url, via_config
+                    ),
                 ),
                 "method": "GET",
                 "headers": {
@@ -50,3 +71,20 @@ def view_youtube_video(request, url, **kwargs):
             }
         },
     }
+
+
+def _get_transcript_id(youtube_service, url, via_config):
+    # Try the `via.video.lang` param first
+    if transcript_id := via_config.get("video", {}).get("lang"):
+        return transcript_id
+
+    # Then look up a transcript matching our preferences
+    video = youtube_service.get_video_info(video_url=url)
+    if video.has_captions and (
+        caption_track := video.caption.find_matching_track(CAPTION_TRACK_PREFERENCES)
+    ):
+        return caption_track.id
+
+    # This shouldn't be possible to get to if this was an option, but we need a
+    # fall-back. We could also fail here instead?
+    return "en.a"