fix #975

Source/C++/Core/Ap4TrunAtom.cpp

@@ -37,6 +37,11 @@
 +---------------------------------------------------------------------*/
 AP4_DEFINE_DYNAMIC_CAST_ANCHOR(AP4_TrunAtom)
 
+/*----------------------------------------------------------------------
+|   constants
++---------------------------------------------------------------------*/
+#define AP4_TRUN_MAX_SAMPLE_COUNT 0xFFFFFF
+
 /*----------------------------------------------------------------------
 |   AP4_TrunAtom::Create
 +---------------------------------------------------------------------*/
@@ -143,14 +148,15 @@ AP4_TrunAtom::AP4_TrunAtom(AP4_UI32        size,
     }
 
     int record_fields_count = (int)ComputeRecordFieldsCount(flags);
-    if (!record_fields_count) {
-        // nothing to read
-        return;
-    }
-
-    if ((bytes_left / (record_fields_count*4)) < sample_count) {
-        // not enough data for all samples, the format is invalid
-        return;
+    if (record_fields_count) {
+        if ((bytes_left / (record_fields_count*4)) < sample_count) {
+            // not enough data for all samples, the format is invalid
+            return;
+        }
+    } else {
+        if (sample_count > AP4_TRUN_MAX_SAMPLE_COUNT) {
+            return;
+        }
     }
 
     if (AP4_FAILED(m_Entries.SetItemCount(sample_count))) {