add the tremolo effect

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

@@ -103,7 +103,8 @@ class AudioHandleActivity : BaseActivity() {
                 R.id.btn_audio_encode,
                 R.id.btn_pcm_concat,
                 R.id.btn_audio_speed,
-                R.id.btn_audio_echo
+                R.id.btn_audio_echo,
+                R.id.btn_audio_tremolo
         )
     }
 
@@ -227,6 +228,13 @@ class AudioHandleActivity : BaseActivity() {
                 val echoPath = PATH + File.separator + "echo.mp3"
                 commandLine = FFmpegUtil.audioEcho(srcFile, echo, echoPath)
             }
+            R.id.btn_audio_tremolo //tremolo effect
+            -> {
+                val frequency = 5 // range from 0.1 to 20000.0
+                val depth = 0.9f // range from 0 to 1
+                val tremoloPath = PATH + File.separator + "tremolo.mp3"
+                commandLine = FFmpegUtil.audioTremolo(srcFile, frequency, depth, tremoloPath)
+            }
             else -> {
             }
         }

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

@@ -103,6 +103,23 @@ public class FFmpegUtil {
         return echoCmd.split(" ");
     }
 
+    /**
+     * Set tremolo effect, sinusoidal amplitude modulation
+     *
+     * @param inputPath  input file
+     * @param frequency  frequency
+     * @param depth      depth
+     * @param outputPath output file
+     * @return mix success or not
+     */
+    public static String[] audioTremolo(String inputPath, int frequency, float depth, String outputPath) {
+        // frequency [0.1, 20000.0], Default is 5
+        // depth (0, 1], Default is 0.5
+        String tremoloCmd = "ffmpeg -i %s -af tremolo=%d:%f %s";
+        tremoloCmd = String.format(Locale.getDefault(), tremoloCmd, inputPath, frequency, depth, outputPath);
+        return tremoloCmd.split(" ");
+    }
+
     /**
      * mux audio and video together
      *

app/src/main/res/layout/activity_audio_handle.xml

@@ -58,7 +58,8 @@
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:text="@string/audio_encode"
-            android:layout_marginTop="10dp" />
+            android:layout_marginTop="10dp"
+            android:visibility="gone"/>
 
         <Button
             android:id="@+id/btn_pcm_concat"
@@ -82,6 +83,13 @@
             android:text="@string/audio_echo"
             android:layout_marginTop="10dp" />
 
+        <Button
+            android:id="@+id/btn_audio_tremolo"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:text="@string/audio_tremolo"
+            android:layout_marginTop="10dp" />
+
     </LinearLayout>
 
     <include

app/src/main/res/values-en/strings.xml

@@ -10,6 +10,7 @@
     <string name="pcm_concat">PCM concat</string>
     <string name="audio_speed">Audio speed</string>
     <string name="audio_echo">Echo effect</string>
+    <string name="audio_tremolo">Tremolo effect</string>
     <string name="audio_effect">Audio effect</string>
     <string name="audio_equalizer">Audio equalizer:</string>
     <string name="audio_style">Audio style:</string>

app/src/main/res/values/strings.xml

@@ -10,6 +10,7 @@
     <string name="pcm_concat">PCM合并</string>
     <string name="audio_speed">音频速度</string>
     <string name="audio_echo">空灵效果</string>
+    <string name="audio_tremolo">惊悚效果</string>
     <string name="audio_effect">音乐均衡器</string>
     <string name="audio_equalizer">均衡器:</string>
     <string name="audio_style">风格:</string>