add &'static str error variant

src/main.rs

@@ -18,6 +18,7 @@ enum Error {
     Io(io::Error),
     Ffmpeg(ffmpeg::Error),
     String(String),
+    Str(&'static str),
 }
 
 impl From<ffmpeg::Error> for Error {
@@ -38,6 +39,12 @@ impl From<String> for Error {
     }
 }
 
+impl From<&'static str> for Error {
+    fn from(v: &'static str) -> Error {
+        Error::Str(v)
+    }
+}
+
 fn filter(
     decoder: &codec::decoder::Audio,
     encoder: &codec::encoder::Audio,