Fix preview of imgur and Tenor URLs. (#11669)

By scraping Open Graph information from the HTML even
when an autodiscovery endpoint is found. The results are
then combined to capture as much information as possible
from the page.

1 files changed, 6 insertions, 1 deletions

diff --git a/docs/development/url_previews.md b/docs/development/url_previews.md
index aff3813609..154b9a5e12 100644
--- a/docs/development/url_previews.md
+++ b/docs/development/url_previews.md
@@ -35,7 +35,12 @@ When Synapse is asked to preview a URL it does the following:
    5. If the media is HTML:
       1. Decodes the HTML via the stored file.
       2. Generates an Open Graph response from the HTML.
-      3. If an image exists in the Open Graph response:
+      3. If a JSON oEmbed URL was found in the HTML via autodiscovery:
+         1. Downloads the URL and stores it into a file via the media storage provider
+            and saves the local media metadata.
+         2. Convert the oEmbed response to an Open Graph response.
+         3. Override any Open Graph data from the HTML with data from oEmbed.
+      4. If an image exists in the Open Graph response:
          1. Downloads the URL and stores it into a file via the media storage
             provider and saves the local media metadata.
          2. Generates thumbnails.