Auto locate transcoder binary

Signed-off-by: Andrew DeMaria <lostonamountain@gmail.com>

libresonic-main/src/main/java/org/libresonic/player/service/TranscodingService.java

@@ -329,8 +329,8 @@ public class TranscodingService {
             title = "Unknown Artist";
         }
 
-        List<String> result = new LinkedList<String>(Arrays.asList(StringUtil.split(command)));
-        result.set(0, getTranscodeDirectory().getPath() + File.separatorChar + result.get(0));
+        List<String> result = new LinkedList<>(Arrays.asList(StringUtil.split(command)));
+        result.set(0, getExecutableName(result));
 
         File tmpFile = null;
 
@@ -381,6 +381,20 @@ public class TranscodingService {
         return new TranscodeInputStream(new ProcessBuilder(result), in, tmpFile);
     }
 
+    private String getExecutableName(List<String> transcodeTokens) {
+        String executableName = transcodeTokens.get(0);
+        String transcodeDirectoryPath = getTranscodeDirectory().getPath() + File.separatorChar + executableName;
+        File file = new File(transcodeDirectoryPath);
+        if(file.exists()) {
+            if(!file.canExecute()) {
+                throw new RuntimeException("Transcoder is not executable at " + transcodeDirectoryPath);
+            }
+            return transcodeDirectoryPath;
+        } else {
+            return executableName;
+        }
+    }
+
     /**
      * Returns an applicable transcoding for the given file and player, or <code>null</code> if no
      * transcoding should be done.