process mp4 file thumbnailing

spec/lib/loaded_media_spec.rb

@@ -21,6 +21,9 @@ RSpec.describe LoadedMedia do
       .join("test/fixtures/files/images/e621-5421402-animated.webm")
       .to_s
   end
+  let(:mp4_fixture_path) do
+    Rails.root.join("test/fixtures/files/images/bsky-3l6tnjkcgw72y.mp4").to_s
+  end
 
   let(:thumbnail_options) do
     LoadedMedia::ThumbnailOptions.new(
@@ -53,14 +56,23 @@ RSpec.describe LoadedMedia do
     end
 
     context "with a webm file" do
-      it "creates a LoadedMedia::Webm instance" do
+      it "creates a LoadedMedia::WebmOrMp4 instance" do
         media = LoadedMedia.from_file("video/webm", webm_fixture_path)
 
-        expect(media).to be_a(LoadedMedia::Webm)
+        expect(media).to be_a(LoadedMedia::WebmOrMp4)
         expect(media.num_frames).to eq(908)
       end
     end
 
+    context "with an mp4 file" do
+      it "creates a LoadedMedia::WebmOrMp4 instance" do
+        media = LoadedMedia.from_file("video/mp4", mp4_fixture_path)
+
+        expect(media).to be_a(LoadedMedia::WebmOrMp4)
+        expect(media.num_frames).to eq(22)
+      end
+    end
+
     context "with an unsupported file type" do
       it "returns nil" do
         media = LoadedMedia.from_file("application/pdf", jpeg_fixture_path)
@@ -155,5 +167,30 @@ RSpec.describe LoadedMedia do
         expect(FileUtils.compare_file(paths[1], paths[2])).to be false
       end
     end
+
+    context "with an mp4 file" do
+      it "can extract a frame and save a thumbnail" do
+        media = LoadedMedia.from_file("video/mp4", mp4_fixture_path)
+
+        output_path = make_output_path(0)
+        media.write_frame_thumbnail(0, output_path, thumbnail_options)
+      end
+
+      it "creates different frames" do
+        media = LoadedMedia.from_file("video/mp4", mp4_fixture_path)
+
+        paths =
+          [0, 10, media.num_frames - 1].map do |frame|
+            output_path = make_output_path(frame)
+            media.write_frame_thumbnail(frame, output_path, thumbnail_options)
+            output_path
+          end
+
+        expect(paths.uniq.length).to eq(3)
+        expect(FileUtils.compare_file(paths[0], paths[1])).to be false
+        expect(FileUtils.compare_file(paths[0], paths[2])).to be false
+        expect(FileUtils.compare_file(paths[1], paths[2])).to be false
+      end
+    end
   end
 end