diff --git a/media/extractors/mp4/MPEG4Extractor.cpp b/media/extractors/mp4/MPEG4Extractor.cpp
index fa562f3..485c0cc 100755
--- a/media/extractors/mp4/MPEG4Extractor.cpp
+++ b/media/extractors/mp4/MPEG4Extractor.cpp
@@ -1060,6 +1060,8 @@
                     // drop it now to reduce our footprint
                     free(mLastTrack->mTx3gBuffer);
                     mLastTrack->mTx3gBuffer = NULL;
+                    mLastTrack->mTx3gFilled = 0;
+                    mLastTrack->mTx3gSize = 0;
                 }
 
             } else if (chunk_type == FOURCC("moov")) {
@@ -2621,6 +2623,10 @@
             // if those apps are compensating for it, we'd break them with such a change
             //
 
+            if (mLastTrack->mTx3gBuffer == NULL) {
+                mLastTrack->mTx3gSize = 0;
+                mLastTrack->mTx3gFilled = 0;
+            }
             if (mLastTrack->mTx3gSize - mLastTrack->mTx3gFilled < chunk_size) {
                 size_t growth = kTx3gGrowth;
                 if (growth < chunk_size) {