MainActivity: use ultrafast preset for ffmpeg

app/src/main/java/io/lowrespalmtree/harvestdawn/MainActivity.kt

@@ -203,6 +203,7 @@ class MainActivity : AppCompatActivity() {
             val command = (
                 "-i $videoPath -i $audioPath"
                 + " -filter_complex amix=duration=longest"
+                + " -preset ultrafast"
                 + " -c:v libx264 -crf 26 -vf scale=$width:trunc(ow/a/2)*2 -pix_fmt yuv420p"
                 + " $durationOpt -y $outputPath"
             )