diff --git a/trunk/src/kernel/srs_kernel_mp4.cpp b/trunk/src/kernel/srs_kernel_mp4.cpp
index 29e58d816..ddcce00be 100644
--- a/trunk/src/kernel/srs_kernel_mp4.cpp
+++ b/trunk/src/kernel/srs_kernel_mp4.cpp
@@ -4791,10 +4791,10 @@ srs_error_t SrsMp4SampleManager::load(SrsMp4MovieBox* moov)
 
 SrsMp4Sample* SrsMp4SampleManager::at(uint32_t index)
 {
-    if (index >= samples.size() - 1) {
-        return NULL;
+    if (index < samples.size()) {
+        return samples.at(index);
     }
-    return samples.at(index);
+    return NULL;
 }
 
 void SrsMp4SampleManager::append(SrsMp4Sample* sample)
diff --git a/trunk/src/utest/srs_utest_kernel.cpp b/trunk/src/utest/srs_utest_kernel.cpp
index b6784b562..7e4d32f11 100644
--- a/trunk/src/utest/srs_utest_kernel.cpp
+++ b/trunk/src/utest/srs_utest_kernel.cpp
@@ -4688,8 +4688,34 @@ VOID TEST(KernelMP4Test, CoverMP4Codec)
         uint16_t ft, ct;
         uint32_t dts, pts, nb_sample;
         uint8_t* sample;
+
+        EXPECT_TRUE(srs_success == dec.read_sample(&ht, &ft, &ct, &dts, &pts, &sample, &nb_sample));
+        EXPECT_EQ(0, (int)dts);
+        EXPECT_EQ(41, nb_sample);
+        EXPECT_EQ(SrsMp4HandlerTypeVIDE, ht);
+        EXPECT_EQ(SrsAudioAacFrameTraitSequenceHeader, ct);
+        srs_freepa(sample);
+
+        EXPECT_TRUE(srs_success == dec.read_sample(&ht, &ft, &ct, &dts, &pts, &sample, &nb_sample));
+        EXPECT_EQ(0, (int)dts);
+        EXPECT_EQ(2, nb_sample);
+        EXPECT_EQ(SrsMp4HandlerTypeSOUN, ht);
+        EXPECT_EQ(SrsAudioAacFrameTraitSequenceHeader, ct);
+        srs_freepa(sample);
+
+        EXPECT_TRUE(srs_success == dec.read_sample(&ht, &ft, &ct, &dts, &pts, &sample, &nb_sample));
+        EXPECT_EQ(0, (int)dts);
+        EXPECT_EQ(87, nb_sample);
+        EXPECT_EQ(SrsMp4HandlerTypeSOUN, ht);
+        EXPECT_NE(SrsAudioAacFrameTraitSequenceHeader, ct);
+        srs_freepa(sample);
+
         EXPECT_TRUE(srs_success == dec.read_sample(&ht, &ft, &ct, &dts, &pts, &sample, &nb_sample));
         EXPECT_EQ(0, (int)dts);
+        EXPECT_EQ(127, nb_sample);
+        EXPECT_EQ(SrsMp4HandlerTypeVIDE, ht);
+        EXPECT_NE(SrsAudioAacFrameTraitSequenceHeader, ct);
+        srs_freepa(sample);
     }
     
     if (true) {