diff --git a/trunk/src/kernel/srs_kernel_mp4.cpp b/trunk/src/kernel/srs_kernel_mp4.cpp
index d042b11be..86e8fbc9c 100644
--- a/trunk/src/kernel/srs_kernel_mp4.cpp
+++ b/trunk/src/kernel/srs_kernel_mp4.cpp
@@ -195,7 +195,8 @@ int SrsMp4Box::sz_header()
 
 int SrsMp4Box::left_space(SrsBuffer* buf)
 {
-    return (int)sz() - (buf->pos() - start_pos);
+    int left = (int)sz() - (buf->pos() - start_pos);
+    return srs_max(0, left);
 }
 
 bool SrsMp4Box::is_ftyp()
@@ -237,6 +238,7 @@ int SrsMp4Box::remove(SrsMp4BoxType bt)
         
         if (box->type == bt) {
             it = boxes.erase(it);
+            srs_freep(box);
         } else {
             ++it;
         }
@@ -245,6 +247,11 @@ int SrsMp4Box::remove(SrsMp4BoxType bt)
     return nb_removed;
 }
 
+void SrsMp4Box::append(SrsMp4Box* box)
+{
+    boxes.push_back(box);
+}
+
 stringstream& SrsMp4Box::dumps(stringstream& ss, SrsMp4DumpContext dc)
 {
     srs_mp4_padding(ss, dc);
@@ -351,6 +358,7 @@ srs_error_t SrsMp4Box::discovery(SrsBuffer* buf, SrsMp4Box** ppbox)
         case SrsMp4BoxTypeSIDX: box = new SrsMp4SegmentIndexBox(); break;
         // Skip some unknown boxes.
         case SrsMp4BoxTypeFREE: case SrsMp4BoxTypeSKIP: case SrsMp4BoxTypePASP:
+        case SrsMp4BoxTypeUUID:
             box = new SrsMp4FreeSpaceBox(type); break;
         default:
             err = srs_error_new(ERROR_MP4_BOX_ILLEGAL_TYPE, "illegal box type=%d", type);
@@ -3229,7 +3237,8 @@ SrsMp4BaseDescriptor::~SrsMp4BaseDescriptor()
 
 int SrsMp4BaseDescriptor::left_space(SrsBuffer* buf)
 {
-    return vlen - (buf->pos() - start_pos);
+    int left = vlen - (buf->pos() - start_pos);
+    return srs_max(0, left);
 }
 
 int SrsMp4BaseDescriptor::nb_bytes()
diff --git a/trunk/src/kernel/srs_kernel_mp4.hpp b/trunk/src/kernel/srs_kernel_mp4.hpp
index cf63031c3..a0ae66149 100644
--- a/trunk/src/kernel/srs_kernel_mp4.hpp
+++ b/trunk/src/kernel/srs_kernel_mp4.hpp
@@ -214,6 +214,8 @@ public:
     // Remove the contained box of specified type.
     // @return The removed count.
     virtual int remove(SrsMp4BoxType bt);
+    // Append a child box.
+    virtual void append(SrsMp4Box* box);
     // Dumps the box and all contained boxes.
     virtual std::stringstream& dumps(std::stringstream& ss, SrsMp4DumpContext dc);
     // Discovery the box from buffer.
diff --git a/trunk/src/utest/srs_utest_mp4.cpp b/trunk/src/utest/srs_utest_mp4.cpp
index 08aada5a9..edcfa37e8 100644
--- a/trunk/src/utest/srs_utest_mp4.cpp
+++ b/trunk/src/utest/srs_utest_mp4.cpp
@@ -198,3 +198,335 @@ VOID TEST(KernelMp4Test, PrintBytes)
     }
 }
 
+VOID TEST(KernelMp4Test, ChildBoxes)
+{
+    SrsMp4Box* box = new SrsMp4Box();
+    EXPECT_TRUE(box->get(SrsMp4BoxTypeFTYP) == NULL);
+
+    SrsMp4Box* ftyp = new SrsMp4FileTypeBox();
+    box->append(ftyp);
+    EXPECT_TRUE(box->get(SrsMp4BoxTypeFTYP) == ftyp);
+
+    box->remove(SrsMp4BoxTypeFTYP);
+    EXPECT_TRUE(box->get(SrsMp4BoxTypeFTYP) == NULL);
+
+    srs_freep(box);
+}
+
+VOID TEST(KernelMp4Test, DiscoveryBox)
+{
+    srs_error_t err;
+    SrsMp4Box* pbox;
+
+    if (true) {
+        SrsBuffer b;
+        HELPER_ASSERT_FAILED(SrsMp4Box::discovery(&b, &pbox));
+    }
+
+    if (true) {
+        uint8_t data[] = {0,0,0,1, 0,0,0,0};
+        SrsBuffer b((char*)data, sizeof(data));
+        HELPER_ASSERT_FAILED(SrsMp4Box::discovery(&b, &pbox));
+    }
+
+    if (true) {
+        uint8_t data[] = {0,0,0,1, 0,0,0,1,0,0,0,0};
+        SrsBuffer b((char*)data, sizeof(data));
+        HELPER_ASSERT_FAILED(SrsMp4Box::discovery(&b, &pbox));
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeEDTS); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeEDTS, pbox->type);
+        srs_freep(pbox);
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeELST); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeELST, pbox->type);
+        srs_freep(pbox);
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeURN); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeURN, pbox->type);
+        srs_freep(pbox);
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeCTTS); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeCTTS, pbox->type);
+        srs_freep(pbox);
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeCO64); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeCO64, pbox->type);
+        srs_freep(pbox);
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeUDTA); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeUDTA, pbox->type);
+        srs_freep(pbox);
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeMVEX); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeMVEX, pbox->type);
+        srs_freep(pbox);
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeTREX); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeTREX, pbox->type);
+        srs_freep(pbox);
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeSTYP); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeSTYP, pbox->type);
+        srs_freep(pbox);
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeMOOF); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeMOOF, pbox->type);
+        srs_freep(pbox);
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeMFHD); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeMFHD, pbox->type);
+        srs_freep(pbox);
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeTRAF); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeTRAF, pbox->type);
+        srs_freep(pbox);
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeTFHD); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeTFHD, pbox->type);
+        srs_freep(pbox);
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeTFDT); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeTFDT, pbox->type);
+        srs_freep(pbox);
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeTRUN); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeTRUN, pbox->type);
+        srs_freep(pbox);
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeSIDX); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeSIDX, pbox->type);
+        srs_freep(pbox);
+    }
+}
+
+VOID TEST(KernelMp4Test, UUIDBoxDecode)
+{
+    srs_error_t err;
+    SrsMp4Box* pbox;
+
+    if (true) {
+        uint8_t data[24];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeUUID); b.skip(-24);
+        SrsMp4Box box;
+        HELPER_ASSERT_FAILED(box.decode(&b));
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeUUID); b.skip(-8);
+        SrsMp4Box box;
+        HELPER_ASSERT_FAILED(box.decode(&b));
+    }
+
+    if (true) {
+        uint8_t data[16];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(1); b.write_8bytes(0x80000000LL); b.write_4bytes(SrsMp4BoxTypeUUID); b.skip(-16);
+        SrsMp4Box box;
+        HELPER_ASSERT_FAILED(box.decode(&b));
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(1); b.write_4bytes(SrsMp4BoxTypeUUID); b.skip(-8);
+        SrsMp4Box box;
+        HELPER_ASSERT_FAILED(box.decode(&b));
+    }
+
+    if (true) {
+        SrsBuffer b;
+        SrsMp4Box box;
+        HELPER_ASSERT_FAILED(box.decode(&b));
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(0); b.write_4bytes(SrsMp4BoxTypeUUID); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeUUID, pbox->type);
+        HELPER_EXPECT_SUCCESS(pbox->decode(&b));
+        srs_freep(pbox);
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(8); b.write_4bytes(SrsMp4BoxTypeUUID); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeUUID, pbox->type);
+        srs_freep(pbox);
+    }
+
+    if (true) {
+        uint8_t data[8];
+        SrsBuffer b((char*)data, sizeof(data));
+        b.write_4bytes(0); b.write_4bytes(SrsMp4BoxTypeUUID); b.skip(-8);
+        HELPER_ASSERT_SUCCESS(SrsMp4Box::discovery(&b, &pbox));
+        ASSERT_EQ(SrsMp4BoxTypeUUID, pbox->type);
+        srs_freep(pbox);
+    }
+}
+
+VOID TEST(KernelMp4Test, UUIDBoxEncode)
+{
+    srs_error_t err;
+
+    if (true) {
+        char data[8];
+        SrsBuffer b(data, 8);
+
+        SrsMp4Box box;
+        box.type = SrsMp4BoxTypeFREE;
+        box.usertype.resize(8);
+        ASSERT_EQ(8, box.nb_bytes());
+        HELPER_ASSERT_SUCCESS(box.encode(&b));
+    }
+
+    if (true) {
+        char data[24];
+        SrsBuffer b(data, 24);
+
+        SrsMp4Box box;
+        box.type = SrsMp4BoxTypeUUID;
+        box.usertype.resize(16);
+        ASSERT_EQ(24, box.nb_bytes());
+        HELPER_ASSERT_SUCCESS(box.encode(&b));
+    }
+}
+
+VOID TEST(KernelMp4Test, FullBoxDump)
+{
+    if (true) {
+        stringstream ss;
+        SrsMp4DumpContext dc;
+        SrsMp4FileTypeBox box;
+        box.major_brand = SrsMp4BoxBrandISO2;
+        box.compatible_brands.push_back(SrsMp4BoxBrandISOM);
+        box.dumps(ss, dc);
+
+        string v = ss.str();
+        EXPECT_STREQ("ftyp, 0B, brands:iso2,0(isom)\n", v.c_str());
+    }
+
+    if (true) {
+        stringstream ss;
+        SrsMp4DumpContext dc;
+        SrsMp4FullBox box;
+        box.type = SrsMp4BoxTypeFTYP;
+        box.version = 1;
+        box.flags = 0x02;
+        box.dumps(ss, dc);
+
+        string v = ss.str();
+        EXPECT_STREQ("ftyp, 0B, FB(4B,V1,0x02)\n", v.c_str());
+    }
+
+    if (true) {
+        stringstream ss;
+        SrsMp4DumpContext dc;
+        SrsMp4FullBox box;
+        box.type = SrsMp4BoxTypeFTYP;
+        box.version = 1;
+        box.dumps(ss, dc);
+
+        string v = ss.str();
+        EXPECT_STREQ("ftyp, 0B, FB(4B,V1,0x00)\n", v.c_str());
+    }
+
+    if (true) {
+        stringstream ss;
+        SrsMp4DumpContext dc;
+        SrsMp4FullBox box;
+        box.type = SrsMp4BoxTypeFTYP;
+        box.dumps(ss, dc);
+
+        string v = ss.str();
+        EXPECT_STREQ("ftyp, 0B, FB(4B)\n", v.c_str());
+    }
+}
+