fix mix audio: using -vn;

add feature: merger audio

app/src/main/java/com/frank/ffmpeg/activity/AudioHandleActivity.kt

@@ -193,8 +193,13 @@ class AudioHandleActivity : BaseActivity() {
                 if (mixSuffix == null || mixSuffix.isEmpty()) {
                     return
                 }
-                val mixFile = PATH + File.separator + "mix" + mixSuffix
+                commandLine = if (mixAudio) {
-                commandLine = FFmpegUtil.mixAudio(srcFile, appendFile, mixFile)
+                    val mixAudio = PATH + File.separator + "mix" + mixSuffix
+                    FFmpegUtil.mixAudio(srcFile, appendFile, mixAudio)
+                } else {
+                    val mergeAudio = PATH + File.separator + "merge" + mixSuffix
+                    FFmpegUtil.mergeAudio(srcFile, appendFile, mergeAudio)
+                }
             }
             R.id.btn_play_audio//use AudioTrack to play audio
             -> {
@@ -316,6 +321,8 @@ class AudioHandleActivity : BaseActivity() {
         private val PATH = Environment.getExternalStorageDirectory().path
 
         private const val useFFmpeg = true
+
+        private const val mixAudio = true
     }
 
 }

app/src/main/java/com/frank/ffmpeg/util/FFmpegUtil.java

@@ -70,21 +70,31 @@ public class FFmpegUtil {
     }
 
     /**
-     * mix one and another audio
+     * mix multiple audio inputs into a single output
      *
      * @param inputPath  input file
-     * @param mixFile    background music
+     * @param mixPath    background music
      * @param outputPath output file
      * @return mix success or not
      */
-    public static String[] mixAudio(String inputPath, String mixFile, String outputPath) {
+    public static String[] mixAudio(String inputPath, String mixPath, String outputPath) {
-        //adjust volume:using '-vol 50', which is form 0 to 100
+        //duration: first shortest longest
-        String mixAudioCmd = "ffmpeg -i %s -i %s -filter_complex amix=inputs=2:duration=first -strict -2 %s";
+        String mixAudioCmd = "ffmpeg -i %s -i %s -filter_complex amix=inputs=2:duration=longest -vn %s";
-        mixAudioCmd = String.format(mixAudioCmd, inputPath, mixFile, outputPath);
+        mixAudioCmd = String.format(mixAudioCmd, inputPath, mixPath, outputPath);
         return mixAudioCmd.split(" ");
     }
     //mixing formula: value = sample1 + sample2 - ((sample1 * sample2) >> 0x10)
 
+    /**
+     * merge multiple audio streams into a single multi-channel stream
+     *
+     */
+    public static String[] mergeAudio(String inputPath, String mergePath, String outputPath) {
+        String mergeCmd = "ffmpeg -i %s -i %s -filter_complex [0:a][1:a]amerge=inputs=2[aout] -map [aout] %s";
+        mergeCmd = String.format(mergeCmd, inputPath, mergePath, outputPath);
+        return mergeCmd.split(" ");
+    }
+
     /**
      * Set echo and delay effect
      *