Support for generating video thumbnails

// FREEBIE

src/org/thoughtcrime/securesms/video/EncryptedMediaDataSource.java

@@ -0,0 +1,64 @@
+package org.thoughtcrime.securesms.video;
+
+
+import android.media.MediaDataSource;
+import android.os.Build;
+import android.support.annotation.RequiresApi;
+
+import org.thoughtcrime.securesms.crypto.DecryptingPartInputStream;
+import org.thoughtcrime.securesms.crypto.MasterSecret;
+import org.thoughtcrime.securesms.util.Util;
+
+import java.io.File;
+import java.io.IOException;
+
+@RequiresApi(api = Build.VERSION_CODES.M)
+public class EncryptedMediaDataSource extends MediaDataSource {
+
+  private final File         mediaFile;
+  private final MasterSecret masterSecret;
+
+  public EncryptedMediaDataSource(MasterSecret masterSecret, File mediaFile) {
+    this.mediaFile    = mediaFile;
+    this.masterSecret = masterSecret;
+  }
+
+  @Override
+  public int readAt(long position, byte[] bytes, int offset, int length) throws IOException {
+    DecryptingPartInputStream inputStream     = new DecryptingPartInputStream(mediaFile, masterSecret);
+    byte[]                    buffer          = new byte[4096];
+    long                      headerRemaining = position;
+
+    while (headerRemaining > 0) {
+      int read = inputStream.read(buffer, 0, Util.toIntExact(Math.min((long)buffer.length, headerRemaining)));
+
+      if (read == -1) return -1;
+
+      headerRemaining -= read;
+    }
+
+    int returnValue = inputStream.read(bytes, offset, length);
+    inputStream.close();
+    return returnValue;
+  }
+
+  @Override
+  public long getSize() throws IOException {
+    DecryptingPartInputStream inputStream = new DecryptingPartInputStream(mediaFile, masterSecret);
+    byte[]                    buffer      = new byte[4096];
+    long                      size        = 0;
+
+    int read;
+
+    while ((read = inputStream.read(buffer)) != -1) {
+      size += read;
+    }
+
+    return size;
+  }
+
+  @Override
+  public void close() throws IOException {
+
+  }
+}