Feature/muted audio fixes #51

lib/src/main/java/com/otaliastudios/transcoder/TranscoderOptions.java

@@ -13,7 +13,7 @@
 import com.otaliastudios.transcoder.source.DataSource;
 import com.otaliastudios.transcoder.source.FileDescriptorDataSource;
 import com.otaliastudios.transcoder.source.FilePathDataSource;
-import com.otaliastudios.transcoder.source.TrimDataSource;
+import com.otaliastudios.transcoder.source.BlankAudioDataSource;
 import com.otaliastudios.transcoder.source.UriDataSource;
 import com.otaliastudios.transcoder.strategy.DefaultAudioStrategy;
 import com.otaliastudios.transcoder.strategy.DefaultVideoStrategies;
@@ -318,6 +318,43 @@ public Builder setAudioResampler(@NonNull AudioResampler audioResampler) {
             return this;
         }
 
+        /**
+         * Generates muted audio data sources if needed
+         * @return The list of audio data sources including the muted sources
+         */
+        private List<DataSource> buildAudioDataSources()
+        {
+            // Check if we have a mix of empty and non-empty data sources
+            // This would cause an error in Engine::computeTrackStatus
+            boolean hasMissingAudioDataSources = false;
+            boolean hasAudioDataSources = false;
+            boolean hasValidAudioDataSources = true;
+            for (DataSource dataSource : audioDataSources) {
+                if (dataSource.getTrackFormat(TrackType.AUDIO) == null) {
+                    hasMissingAudioDataSources = true;
+                } else {
+                    hasAudioDataSources = true;
+                }
+                if (hasAudioDataSources && hasMissingAudioDataSources) {
+                    hasValidAudioDataSources = false;
+                    break;
+                }
+            }
+            if (hasValidAudioDataSources) {
+                return audioDataSources;
+            }
+            // Fix the audioDataSources by replacing the empty data source by muted data source
+            List<DataSource> result = new ArrayList<>();
+            for (DataSource dataSource : audioDataSources) {
+                if (dataSource.getTrackFormat(TrackType.AUDIO) != null) {
+                    result.add(dataSource);
+                } else {
+                    result.add(new BlankAudioDataSource(dataSource.getDurationUs()));
+                }
+            }
+            return result;
+        }
+
         @NonNull
         public TranscoderOptions build() {
             if (listener == null) {
@@ -354,7 +391,7 @@ public TranscoderOptions build() {
             }
             TranscoderOptions options = new TranscoderOptions();
             options.listener = listener;
-            options.audioDataSources = audioDataSources;
+            options.audioDataSources = buildAudioDataSources();
             options.videoDataSources = videoDataSources;
             options.dataSink = dataSink;
             options.listenerHandler = listenerHandler;

lib/src/main/java/com/otaliastudios/transcoder/internal/MediaFormatConstants.java

@@ -53,6 +53,7 @@ public class MediaFormatConstants {
     // Audio formats
     // from MediaFormat of API level >= 21
     public static final String MIMETYPE_AUDIO_AAC = "audio/mp4a-latm";
+    public static final String MIMETYPE_AUDIO_RAW = "audio/raw";
 
     private MediaFormatConstants() { }
 }

lib/src/main/java/com/otaliastudios/transcoder/source/BlankAudioDataSource.java

@@ -0,0 +1,117 @@
+package com.otaliastudios.transcoder.source;
+
+import android.media.MediaFormat;
+
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+
+import com.otaliastudios.transcoder.engine.TrackType;
+
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+
+import static com.otaliastudios.transcoder.internal.MediaFormatConstants.MIMETYPE_AUDIO_RAW;
+
+/**
+ * A {@link DataSource} that provides a silent audio track of the a specific duration.
+ * This class can be used to concatenate a DataSources that has a video track only with another
+ * that has both video and audio track.
+ */
+public class BlankAudioDataSource implements DataSource {
+    private final static String TAG = BlankAudioDataSource.class.getSimpleName();
+
+    private static final int CHANNEL_COUNT = 2;
+    private static final int SAMPLE_RATE = 44100;
+    private static final int BITS_PER_SAMPLE = 16;
+    private static final int BIT_RATE = CHANNEL_COUNT * SAMPLE_RATE * BITS_PER_SAMPLE;
+    private static final double SAMPLES_PER_PERIOD = 2048;
+    private static final double PERIOD_TIME_SECONDS = SAMPLES_PER_PERIOD / SAMPLE_RATE;
+    private static final long PERIOD_TIME_US = (long) (1000000 * PERIOD_TIME_SECONDS);
+    private static final int PERIOD_SIZE = (int) (PERIOD_TIME_SECONDS * BIT_RATE / 8);
+
+    private final long durationUs;
+    private final ByteBuffer byteBuffer;
+    private final MediaFormat audioFormat;
+
+    private long currentTimestampUs = 0L;
+
+    public BlankAudioDataSource(long durationUs) {
+        this.durationUs = durationUs;
+        this.byteBuffer = ByteBuffer.allocateDirect(PERIOD_SIZE).order(ByteOrder.nativeOrder());
+        this.audioFormat = new MediaFormat();
+        audioFormat.setString(MediaFormat.KEY_MIME, MIMETYPE_AUDIO_RAW);
+        audioFormat.setInteger(MediaFormat.KEY_BIT_RATE, BIT_RATE);
+        audioFormat.setInteger(MediaFormat.KEY_CHANNEL_COUNT, CHANNEL_COUNT);
+        audioFormat.setInteger(MediaFormat.KEY_MAX_INPUT_SIZE, PERIOD_SIZE);
+        audioFormat.setInteger(MediaFormat.KEY_SAMPLE_RATE, SAMPLE_RATE);
+    }
+
+    @Override
+    public int getOrientation() {
+        return 0;
+    }
+
+    @Nullable
+    @Override
+    public double[] getLocation() {
+        return null;
+    }
+
+    @Override
+    public long getDurationUs() {
+        return durationUs;
+    }
+
+    @Nullable
+    @Override
+    public MediaFormat getTrackFormat(@NonNull TrackType type) {
+        return (type == TrackType.AUDIO) ? audioFormat : null;
+    }
+
+    @Override
+    public void selectTrack(@NonNull TrackType type) {
+        // Nothing to do
+    }
+
+    @Override
+    public long seekTo(long desiredTimestampUs) {
+        currentTimestampUs = desiredTimestampUs;
+        return desiredTimestampUs;
+    }
+
+    @Override
+    public boolean canReadTrack(@NonNull TrackType type) {
+        return type == TrackType.AUDIO;
+    }
+
+    @Override
+    public void readTrack(@NonNull Chunk chunk) {
+        byteBuffer.clear();
+        chunk.buffer = byteBuffer;
+        chunk.isKeyFrame = true;
+        chunk.timestampUs = currentTimestampUs;
+        chunk.bytes = PERIOD_SIZE;
+
+        currentTimestampUs += PERIOD_TIME_US;
+    }
+
+    @Override
+    public long getReadUs() {
+        return currentTimestampUs;
+    }
+
+    @Override
+    public boolean isDrained() {
+        return currentTimestampUs >= getDurationUs();
+    }
+
+    @Override
+    public void releaseTrack(@NonNull TrackType type) {
+        // Nothing to do
+    }
+
+    @Override
+    public void rewind() {
+        currentTimestampUs = 0;
+    }
+}