diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index 76fb251fa8..860e331b19 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -648,6 +648,23 @@ static struct mpeg4_bit_rate_values calculate_mpeg4_bit_rates(MOVTrack *track)
     struct mpeg4_bit_rate_values bit_rates = { 0 };
 
     bit_rates.avg_bit_rate = compute_avg_bitrate(track);
+    if (!bit_rates.avg_bit_rate) {
+        // if the average bit rate cannot be calculated at this point, such as
+        // in the case of fragmented MP4, utilize the following values as
+        // fall-back in priority order:
+        //
+        // 1. average bit rate property
+        // 2. bit rate (usually average over the whole clip)
+        // 3. maximum bit rate property
+
+        if (props && props->avg_bitrate) {
+            bit_rates.avg_bit_rate = props->avg_bitrate;
+        } else if (track->par->bit_rate) {
+            bit_rates.avg_bit_rate = track->par->bit_rate;
+        } else if (props && props->max_bitrate) {
+            bit_rates.avg_bit_rate = props->max_bitrate;
+        }
+    }
 
     // (FIXME should be max rate in any 1 sec window)
     bit_rates.max_bit_rate = FFMAX(track->par->bit_rate,
diff --git a/tests/ref/lavf/ismv b/tests/ref/lavf/ismv
index e7361705fa..ac7f72ba33 100644
--- a/tests/ref/lavf/ismv
+++ b/tests/ref/lavf/ismv
@@ -1,9 +1,9 @@
-4c6bc5ac805a76bbbd886a69d2e61554 *tests/data/lavf/lavf.ismv
+48fb8d7a5d19bd60f3a49ccf4b7d6593 *tests/data/lavf/lavf.ismv
 313169 tests/data/lavf/lavf.ismv
 tests/data/lavf/lavf.ismv CRC=0x9d9a638a
-18678627921460328ea3fed238d0d57d *tests/data/lavf/lavf.ismv
+d19cd8e310a2e94fe0a0d11c5dc29217 *tests/data/lavf/lavf.ismv
 322075 tests/data/lavf/lavf.ismv
 tests/data/lavf/lavf.ismv CRC=0xe8130120
-b9a858caf55b1eff2273e746e9f72dc4 *tests/data/lavf/lavf.ismv
+3b6023766845b51b075aed474c00f73c *tests/data/lavf/lavf.ismv
 312546 tests/data/lavf/lavf.ismv
 tests/data/lavf/lavf.ismv CRC=0x9d9a638a