Add framerate parameter option to HTTPs

Some HTTP (a.g. JPEG or MJPEG) needs set the input framerate explicitly.

internal/ffmpeg/ffmpeg.go

@@ -144,6 +144,11 @@ func parseArgs(s string) *ffmpeg.Args {
 		switch s[:i] {
 		case "http", "https", "rtmp":
 			args.Input = inputTemplate("http", s, query)
+			// Some HTTP-JPEG, HTTP-MJPEG needs the input framerate explicitly
+			if query["framerate"] != nil {
+				args.Input = "-framerate " + query["framerate"][0] + " " + args.Input
+				query.Del("framerate")
+			}
 		case "rtsp", "rtsps":
 			// https://ffmpeg.org/ffmpeg-protocols.html#rtsp
 			// skip unnecessary input tracks