Support image clips/gifs (#3583)

Co-authored-by: WithoutPants <53250216+WithoutPants@users.noreply.github.com>

pkg/ffmpeg/transcoder/image.go

@@ -10,6 +10,7 @@ var ErrUnsupportedFormat = errors.New("unsupported image format")
 
 type ImageThumbnailOptions struct {
 	InputFormat   ffmpeg.ImageFormat
+	OutputFormat  ffmpeg.ImageFormat
 	OutputPath    string
 	MaxDimensions int
 	Quality       int
@@ -29,12 +30,15 @@ func ImageThumbnail(input string, options ImageThumbnailOptions) ffmpeg.Args {
 		VideoFilter(videoFilter).
 		VideoCodec(ffmpeg.VideoCodecMJpeg)
 
+	args = append(args, "-frames:v", "1")
+
 	if options.Quality > 0 {
 		args = args.FixedQualityScaleVideo(options.Quality)
 	}
 
 	args = args.ImageFormat(ffmpeg.ImageFormatImage2Pipe).
-		Output(options.OutputPath)
+		Output(options.OutputPath).
+		ImageFormat(options.OutputFormat)
 
 	return args
 }