diff --git a/common/src/main/java/ctbrec/recorder/download/hls/MergedHlsDownload.java b/common/src/main/java/ctbrec/recorder/download/hls/MergedHlsDownload.java
index 8257d60b..773c8089 100644
--- a/common/src/main/java/ctbrec/recorder/download/hls/MergedHlsDownload.java
+++ b/common/src/main/java/ctbrec/recorder/download/hls/MergedHlsDownload.java
@@ -8,8 +8,11 @@ import java.net.URL;
 import java.nio.file.Files;
 import java.security.InvalidKeyException;
 import java.security.NoSuchAlgorithmException;
+import java.time.Duration;
 import java.util.Arrays;
 
+import org.jcodec.containers.mp4.MP4Util;
+import org.jcodec.containers.mp4.boxes.MovieBox;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -151,4 +154,16 @@ public class MergedHlsDownload extends HlsDownload {
             response.close();
         }
     }
+
+    @Override
+    public Duration getLength() {
+        try {
+            MovieBox movieBox = MP4Util.parseMovie(finalFile);
+            double lengthInSeconds = (double) movieBox.getDuration() / movieBox.getTimescale();
+            return Duration.ofSeconds((long) Math.ceil(lengthInSeconds));
+        } catch (IOException e) {
+            LOG.error("Couldn't determine length of MP4 file {}", getTarget(), e);
+            return Duration.ofSeconds(0);
+        }
+    }
 }