fix case when video has no audio, but separate audio is set. add test case for it

lib/src/filter/mod.rs

@@ -429,6 +429,7 @@ pub fn filter_chains(
             .as_ref()
             .and_then(|p| p.audio_streams.get(i as usize))
             .is_some()
+            || Path::new(&node.audio).is_file()
         {
             extend_audio(node, &mut filters, i);
         } else if !node.is_live.unwrap_or(false) {

tests/src/engine_cmd.rs

@@ -97,6 +97,40 @@ fn dual_audio_input() {
     assert_eq!(media.filter, test_filter_cmd);
 }
 
+#[test]
+fn video_separate_audio_input() {
+    let mut config = PlayoutConfig::new(Some("../assets/ffplayout.yml".to_string()));
+    config.out.mode = Stream;
+    config.processing.audio_tracks = 1;
+    config.processing.add_logo = false;
+
+    let mut media_obj = Media::new(0, "./assets/no_audio.mp4", true);
+    media_obj.audio = "./assets/audio.mp3".to_string();
+    let media = gen_source(&config, media_obj, &Arc::new(Mutex::new(vec![])));
+
+    let test_filter_cmd = Some(vec_strings![
+        "-filter_complex",
+        "[0:v:0]scale=1024:576[vout0];[1:a:0]anull[aout0]",
+        "-map",
+        "[vout0]",
+        "-map",
+        "[aout0]"
+    ]);
+
+    assert_eq!(
+        media.cmd,
+        Some(vec_strings![
+            "-i",
+            "./assets/no_audio.mp4",
+            "-i",
+            "./assets/audio.mp3",
+            "-t",
+            "30"
+        ])
+    );
+    assert_eq!(media.filter, test_filter_cmd);
+}
+
 #[test]
 fn video_audio_stream() {
     let mut config = PlayoutConfig::new(Some("../assets/ffplayout.yml".to_string()));