Don't allow uploading videos with unsupported video codecs.
The only video codecs we allow for MP4 files are H.264 and VP9. Other
codecs, including H.265 (aka HEVC), MPEG-4 part 2, and AV1, are
disallowed because they're not universally supported by browsers.
Firefox doesn't support H.265 or MPEG-4 part 2, and Safari doesn't
support AV1.
Additionally, don't allow videos with multiple video tracks, multiple
audio tracks, or no video tracks. Multiple video and audio tracks are
disallowed because they're rare and for moderation purposes, we don't
want people hiding content in extra tracks.
These restrictions really only apply to MP4 videos, since WebM files
don't support multiple video or audio tracks and only support a limited
number of codecs (VP8 and VP9 for videos, Vorbis and Opus for audio).
There are currently 22 posts with unsupported video codecs:
* https://danbooru.donmai.us/posts?tags=video+is:mp4+-exif:Track1:CompressorID=avc1+-exif:Track2:CompressorID=avc1+-exif:Track1:CompressorID=vp09+-exif:Track2:CompressorID=vp09 # AVC1 is H.264
There is one post that has multiple audio tracks:
* https://danbooru.donmai.us/posts/2382057
* Increase the default thumbnail size from small (150x150) to medium (180x180).
* Change the mobile layout to use three posts per row instead of two for small thumbnails.
Parent/child posts are still 150x150 to avoid taking up even more space above posts.
Show the length of videos and animated posts in the thumbnail. The
length is shown the top left corner in MM:SS format. This replaces the
play button icon.
Show a speaker icon instead of a music note icon for posts with sound.
Doing this requires doing `.includes(:media_asset)` in a bunch of
places to avoid N+1 queries when we access the post's duration.
Refactor the post preview html to use the ViewComponent framework. This
lets us encapsulate all the HTML, CSS, and helper methods for a UI
component in a single place.
See https://viewcomponent.org.
