perf: correct `ffmpeg` params for efficient video previews

-ss before -i ("When used as an output option (before an output url), decodes but discards input until the timestamps reach position. ")
discard all non-keyframes
turn off accurate seek

src/previews/video.rs

@@ -30,9 +30,12 @@ impl<'a> Previewable for VideoPath<'a> {
         let outfile = tempfile::Builder::new().suffix(".webp").tempfile()?;
         let thumbnail_cmd = Command::new("ffmpeg")
             .args(["-threads", "1"])
+            .args(["-discard", "nokey"])
+            .args(["-noaccurate_seek"])
+            .args(["-ss", &(90f64.min(duration / 2.0)).to_string()])
             .args(["-i", &self.0.to_string_lossy()])
             .args(["-vframes", "1"])
-            .args(["-ss", &(90f64.min(duration / 2.0)).to_string()])
+            .args(["-vsync", "passthrough"])
             .arg(&*outfile.path().to_string_lossy())
             .arg("-y")
             .output()?;