Better error reporting when ffprobe fails.

src/lib.rs

@@ -297,7 +297,7 @@ fn json_metadata_for_path<P: AsRef<Path> + AsRef<OsStr>>(path: P) -> Result<Stri
     ])
     .arg(Path::new("./").join(path));
     info!(target: "json", "cmd {:?}", cmd);
-    let output = cmd.output()?;
+    let output = cmd.output().context(format!("failed to run {:?}", cmd))?;
     if output.status.success() {
         return Ok(String::from_utf8(output.stdout)?);
     }
@@ -617,7 +617,7 @@ impl MovieLibrary {
                         Some((path.to_string_lossy().into_owned(), json))
                     }
                     Err(e) => {
-                        error!("{}", e);
+                        error!("Failed to open {}: {}", path.to_string_lossy(), e);
                         None
                     }
                 }