diff --git a/include/media/stagefright/DataSource.h b/include/media/stagefright/DataSource.h
index 6f7dc38..9d2cff6 100644
--- a/include/media/stagefright/DataSource.h
+++ b/include/media/stagefright/DataSource.h
@@ -28,6 +28,7 @@
 
 namespace android {
 
+struct AMessage;
 class String8;
 
 class DataSource : public RefBase {
@@ -59,10 +60,14 @@
 
     ////////////////////////////////////////////////////////////////////////////
 
-    bool sniff(String8 *mimeType, float *confidence);
+    bool sniff(String8 *mimeType, float *confidence, sp<AMessage> *meta);
 
+    // The sniffer can optionally fill in "meta" with an AMessage containing
+    // a dictionary of values that helps the corresponding extractor initialize
+    // its state without duplicating effort already exerted by the sniffer.
     typedef bool (*SnifferFunc)(
-            const sp<DataSource> &source, String8 *mimeType, float *confidence);
+            const sp<DataSource> &source, String8 *mimeType,
+            float *confidence, sp<AMessage> *meta);
 
     static void RegisterSniffer(SnifferFunc func);
     static void RegisterDefaultSniffers();
diff --git a/media/libstagefright/AMRExtractor.cpp b/media/libstagefright/AMRExtractor.cpp
index 70af2da..1b05528 100644
--- a/media/libstagefright/AMRExtractor.cpp
+++ b/media/libstagefright/AMRExtractor.cpp
@@ -87,7 +87,7 @@
       mInitCheck(NO_INIT) {
     String8 mimeType;
     float confidence;
-    if (!SniffAMR(mDataSource, &mimeType, &confidence)) {
+    if (!SniffAMR(mDataSource, &mimeType, &confidence, NULL)) {
         return;
     }
 
@@ -276,7 +276,8 @@
 ////////////////////////////////////////////////////////////////////////////////
 
 bool SniffAMR(
-        const sp<DataSource> &source, String8 *mimeType, float *confidence) {
+        const sp<DataSource> &source, String8 *mimeType, float *confidence,
+        sp<AMessage> *) {
     char header[9];
 
     if (source->readAt(0, header, sizeof(header)) != sizeof(header)) {
diff --git a/media/libstagefright/DataSource.cpp b/media/libstagefright/DataSource.cpp
index 90a596c..49eac62 100644
--- a/media/libstagefright/DataSource.cpp
+++ b/media/libstagefright/DataSource.cpp
@@ -25,6 +25,7 @@
 
 #include "matroska/MatroskaExtractor.h"
 
+#include <media/stagefright/foundation/AMessage.h>
 #include <media/stagefright/DataSource.h>
 #include <media/stagefright/FileSource.h>
 #include <media/stagefright/MediaErrors.h>
@@ -56,19 +57,23 @@
 Mutex DataSource::gSnifferMutex;
 List<DataSource::SnifferFunc> DataSource::gSniffers;
 
-bool DataSource::sniff(String8 *mimeType, float *confidence) {
+bool DataSource::sniff(
+        String8 *mimeType, float *confidence, sp<AMessage> *meta) {
     *mimeType = "";
     *confidence = 0.0f;
+    meta->clear();
 
     Mutex::Autolock autoLock(gSnifferMutex);
     for (List<SnifferFunc>::iterator it = gSniffers.begin();
          it != gSniffers.end(); ++it) {
         String8 newMimeType;
         float newConfidence;
-        if ((*it)(this, &newMimeType, &newConfidence)) {
+        sp<AMessage> newMeta;
+        if ((*it)(this, &newMimeType, &newConfidence, &newMeta)) {
             if (newConfidence > *confidence) {
                 *mimeType = newMimeType;
                 *confidence = newConfidence;
+                *meta = newMeta;
             }
         }
     }
@@ -92,13 +97,13 @@
 
 // static
 void DataSource::RegisterDefaultSniffers() {
-    RegisterSniffer(SniffMP3);
     RegisterSniffer(SniffMPEG4);
-    RegisterSniffer(SniffAMR);
-    RegisterSniffer(SniffWAV);
-    RegisterSniffer(SniffOgg);
     RegisterSniffer(SniffMatroska);
+    RegisterSniffer(SniffOgg);
+    RegisterSniffer(SniffWAV);
+    RegisterSniffer(SniffAMR);
     RegisterSniffer(SniffMPEG2TS);
+    RegisterSniffer(SniffMP3);
 }
 
 // static
diff --git a/media/libstagefright/MP3Extractor.cpp b/media/libstagefright/MP3Extractor.cpp
index 4058fbc..2e36968 100644
--- a/media/libstagefright/MP3Extractor.cpp
+++ b/media/libstagefright/MP3Extractor.cpp
@@ -22,6 +22,7 @@
 
 #include "include/ID3.h"
 
+#include <media/stagefright/foundation/AMessage.h>
 #include <media/stagefright/DataSource.h>
 #include <media/stagefright/MediaBuffer.h>
 #include <media/stagefright/MediaBufferGroup.h>
@@ -456,15 +457,31 @@
     MP3Source &operator=(const MP3Source &);
 };
 
-MP3Extractor::MP3Extractor(const sp<DataSource> &source)
+MP3Extractor::MP3Extractor(
+        const sp<DataSource> &source, const sp<AMessage> &meta)
     : mDataSource(source),
       mFirstFramePos(-1),
       mFixedHeader(0),
       mByteNumber(0) {
     off_t pos = 0;
     uint32_t header;
-    bool success = Resync(mDataSource, 0, &pos, &header);
-    CHECK(success);
+    bool success;
+
+    int64_t meta_offset;
+    uint32_t meta_header;
+    if (meta != NULL
+            && meta->findInt64("offset", &meta_offset)
+            && meta->findInt32("header", (int32_t *)&meta_header)) {
+        // The sniffer has already done all the hard work for us, simply
+        // accept its judgement.
+        pos = (off_t)meta_offset;
+        header = meta_header;
+
+        success = true;
+    } else {
+        success = Resync(mDataSource, 0, &pos, &header);
+        CHECK(success);
+    }
 
     if (success) {
         mFirstFramePos = pos;
@@ -759,15 +776,20 @@
 }
 
 bool SniffMP3(
-        const sp<DataSource> &source, String8 *mimeType, float *confidence) {
+        const sp<DataSource> &source, String8 *mimeType,
+        float *confidence, sp<AMessage> *meta) {
     off_t pos = 0;
     uint32_t header;
     if (!Resync(source, 0, &pos, &header)) {
         return false;
     }
 
+    *meta = new AMessage;
+    (*meta)->setInt64("offset", pos);
+    (*meta)->setInt32("header", header);
+
     *mimeType = MEDIA_MIMETYPE_AUDIO_MPEG;
-    *confidence = 0.3f;
+    *confidence = 0.2f;
 
     return true;
 }
diff --git a/media/libstagefright/MPEG4Extractor.cpp b/media/libstagefright/MPEG4Extractor.cpp
index 12a1e6e..ba90407 100644
--- a/media/libstagefright/MPEG4Extractor.cpp
+++ b/media/libstagefright/MPEG4Extractor.cpp
@@ -1738,7 +1738,7 @@
         || !memcmp(header, "ftypM4A ", 8) || !memcmp(header, "ftypf4v ", 8)
         || !memcmp(header, "ftypkddi", 8) || !memcmp(header, "ftypM4VP", 8)) {
         *mimeType = MEDIA_MIMETYPE_CONTAINER_MPEG4;
-        *confidence = 0.1;
+        *confidence = 0.4;
 
         return true;
     }
@@ -1805,13 +1805,14 @@
     }
 
     *mimeType = MEDIA_MIMETYPE_CONTAINER_MPEG4;
-    *confidence = 0.3f;
+    *confidence = 0.4f;
 
     return true;
 }
 
 bool SniffMPEG4(
-        const sp<DataSource> &source, String8 *mimeType, float *confidence) {
+        const sp<DataSource> &source, String8 *mimeType, float *confidence,
+        sp<AMessage> *) {
     if (BetterSniffMPEG4(source, mimeType, confidence)) {
         return true;
     }
diff --git a/media/libstagefright/MediaExtractor.cpp b/media/libstagefright/MediaExtractor.cpp
index 56e6136..9bc94de 100644
--- a/media/libstagefright/MediaExtractor.cpp
+++ b/media/libstagefright/MediaExtractor.cpp
@@ -27,6 +27,7 @@
 
 #include "matroska/MatroskaExtractor.h"
 
+#include <media/stagefright/foundation/AMessage.h>
 #include <media/stagefright/DataSource.h>
 #include <media/stagefright/MediaDefs.h>
 #include <media/stagefright/MediaExtractor.h>
@@ -46,10 +47,12 @@
 // static
 sp<MediaExtractor> MediaExtractor::Create(
         const sp<DataSource> &source, const char *mime) {
+    sp<AMessage> meta;
+
     String8 tmp;
     if (mime == NULL) {
         float confidence;
-        if (!source->sniff(&tmp, &confidence)) {
+        if (!source->sniff(&tmp, &confidence, &meta)) {
             LOGV("FAILED to autodetect media content.");
 
             return NULL;
@@ -64,7 +67,7 @@
             || !strcasecmp(mime, "audio/mp4")) {
         return new MPEG4Extractor(source);
     } else if (!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_MPEG)) {
-        return new MP3Extractor(source);
+        return new MP3Extractor(source, meta);
     } else if (!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_AMR_NB)
             || !strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_AMR_WB)) {
         return new AMRExtractor(source);
diff --git a/media/libstagefright/OggExtractor.cpp b/media/libstagefright/OggExtractor.cpp
index 9630092..2c1311a 100644
--- a/media/libstagefright/OggExtractor.cpp
+++ b/media/libstagefright/OggExtractor.cpp
@@ -804,7 +804,8 @@
 }
 
 bool SniffOgg(
-        const sp<DataSource> &source, String8 *mimeType, float *confidence) {
+        const sp<DataSource> &source, String8 *mimeType, float *confidence,
+        sp<AMessage> *) {
     char tmp[4];
     if (source->readAt(0, tmp, 4) < 4 || memcmp(tmp, "OggS", 4)) {
         return false;
diff --git a/media/libstagefright/WAVExtractor.cpp b/media/libstagefright/WAVExtractor.cpp
index 8d820c0..57c1075 100644
--- a/media/libstagefright/WAVExtractor.cpp
+++ b/media/libstagefright/WAVExtractor.cpp
@@ -404,7 +404,8 @@
 ////////////////////////////////////////////////////////////////////////////////
 
 bool SniffWAV(
-        const sp<DataSource> &source, String8 *mimeType, float *confidence) {
+        const sp<DataSource> &source, String8 *mimeType, float *confidence,
+        sp<AMessage> *) {
     char header[12];
     if (source->readAt(0, header, sizeof(header)) < (ssize_t)sizeof(header)) {
         return false;
diff --git a/media/libstagefright/include/AMRExtractor.h b/media/libstagefright/include/AMRExtractor.h
index db49fe4..1cdf36d 100644
--- a/media/libstagefright/include/AMRExtractor.h
+++ b/media/libstagefright/include/AMRExtractor.h
@@ -22,6 +22,7 @@
 
 namespace android {
 
+struct AMessage;
 class String8;
 
 class AMRExtractor : public MediaExtractor {
@@ -49,7 +50,8 @@
 };
 
 bool SniffAMR(
-        const sp<DataSource> &source, String8 *mimeType, float *confidence);
+        const sp<DataSource> &source, String8 *mimeType, float *confidence,
+        sp<AMessage> *);
 
 }  // namespace android
 
diff --git a/media/libstagefright/include/MP3Extractor.h b/media/libstagefright/include/MP3Extractor.h
index 3ce6df3..0e6ccde 100644
--- a/media/libstagefright/include/MP3Extractor.h
+++ b/media/libstagefright/include/MP3Extractor.h
@@ -22,13 +22,14 @@
 
 namespace android {
 
+struct AMessage;
 class DataSource;
 class String8;
 
 class MP3Extractor : public MediaExtractor {
 public:
     // Extractor assumes ownership of "source".
-    MP3Extractor(const sp<DataSource> &source);
+    MP3Extractor(const sp<DataSource> &source, const sp<AMessage> &meta);
 
     virtual size_t countTracks();
     virtual sp<MediaSource> getTrack(size_t index);
@@ -52,7 +53,8 @@
 };
 
 bool SniffMP3(
-        const sp<DataSource> &source, String8 *mimeType, float *confidence);
+        const sp<DataSource> &source, String8 *mimeType, float *confidence,
+        sp<AMessage> *meta);
 
 }  // namespace android
 
diff --git a/media/libstagefright/include/MPEG2TSExtractor.h b/media/libstagefright/include/MPEG2TSExtractor.h
index c96973b..1bf4cd1 100644
--- a/media/libstagefright/include/MPEG2TSExtractor.h
+++ b/media/libstagefright/include/MPEG2TSExtractor.h
@@ -9,6 +9,7 @@
 
 namespace android {
 
+struct AMessage;
 struct AnotherPacketSource;
 struct ATSParser;
 struct DataSource;
@@ -47,7 +48,8 @@
 };
 
 bool SniffMPEG2TS(
-        const sp<DataSource> &source, String8 *mimeType, float *confidence);
+        const sp<DataSource> &source, String8 *mimeType, float *confidence,
+        sp<AMessage> *);
 
 }  // namespace android
 
diff --git a/media/libstagefright/include/MPEG4Extractor.h b/media/libstagefright/include/MPEG4Extractor.h
index c8663d5..1c9cc7e 100644
--- a/media/libstagefright/include/MPEG4Extractor.h
+++ b/media/libstagefright/include/MPEG4Extractor.h
@@ -23,6 +23,7 @@
 
 namespace android {
 
+struct AMessage;
 class DataSource;
 class SampleTable;
 class String8;
@@ -75,7 +76,8 @@
 };
 
 bool SniffMPEG4(
-        const sp<DataSource> &source, String8 *mimeType, float *confidence);
+        const sp<DataSource> &source, String8 *mimeType, float *confidence,
+        sp<AMessage> *);
 
 }  // namespace android
 
diff --git a/media/libstagefright/include/OggExtractor.h b/media/libstagefright/include/OggExtractor.h
index 7066669..1eda025 100644
--- a/media/libstagefright/include/OggExtractor.h
+++ b/media/libstagefright/include/OggExtractor.h
@@ -22,6 +22,7 @@
 
 namespace android {
 
+struct AMessage;
 class DataSource;
 class String8;
 
@@ -53,7 +54,8 @@
 };
 
 bool SniffOgg(
-        const sp<DataSource> &source, String8 *mimeType, float *confidence);
+        const sp<DataSource> &source, String8 *mimeType, float *confidence,
+        sp<AMessage> *);
 
 }  // namespace android
 
diff --git a/media/libstagefright/include/WAVExtractor.h b/media/libstagefright/include/WAVExtractor.h
index 3e847b9..df6d3e7 100644
--- a/media/libstagefright/include/WAVExtractor.h
+++ b/media/libstagefright/include/WAVExtractor.h
@@ -22,6 +22,7 @@
 
 namespace android {
 
+struct AMessage;
 class DataSource;
 class String8;
 
@@ -58,7 +59,8 @@
 };
 
 bool SniffWAV(
-        const sp<DataSource> &source, String8 *mimeType, float *confidence);
+        const sp<DataSource> &source, String8 *mimeType, float *confidence,
+        sp<AMessage> *);
 
 }  // namespace android
 
diff --git a/media/libstagefright/matroska/MatroskaExtractor.cpp b/media/libstagefright/matroska/MatroskaExtractor.cpp
index 71f6587..7c7d69e 100644
--- a/media/libstagefright/matroska/MatroskaExtractor.cpp
+++ b/media/libstagefright/matroska/MatroskaExtractor.cpp
@@ -579,7 +579,8 @@
 }
 
 bool SniffMatroska(
-        const sp<DataSource> &source, String8 *mimeType, float *confidence) {
+        const sp<DataSource> &source, String8 *mimeType, float *confidence,
+        sp<AMessage> *) {
     DataSourceReader reader(source);
     mkvparser::EBMLHeader ebmlHeader;
     long long pos;
diff --git a/media/libstagefright/matroska/MatroskaExtractor.h b/media/libstagefright/matroska/MatroskaExtractor.h
index 7471848..fa20b84 100644
--- a/media/libstagefright/matroska/MatroskaExtractor.h
+++ b/media/libstagefright/matroska/MatroskaExtractor.h
@@ -27,6 +27,7 @@
 
 namespace android {
 
+struct AMessage;
 class String8;
 
 struct DataSourceReader;
@@ -69,7 +70,8 @@
 };
 
 bool SniffMatroska(
-        const sp<DataSource> &source, String8 *mimeType, float *confidence);
+        const sp<DataSource> &source, String8 *mimeType, float *confidence,
+        sp<AMessage> *);
 
 }  // namespace android
 
diff --git a/media/libstagefright/mpeg2ts/MPEG2TSExtractor.cpp b/media/libstagefright/mpeg2ts/MPEG2TSExtractor.cpp
index b287c95..56ca375 100644
--- a/media/libstagefright/mpeg2ts/MPEG2TSExtractor.cpp
+++ b/media/libstagefright/mpeg2ts/MPEG2TSExtractor.cpp
@@ -174,7 +174,8 @@
 ////////////////////////////////////////////////////////////////////////////////
 
 bool SniffMPEG2TS(
-        const sp<DataSource> &source, String8 *mimeType, float *confidence) {
+        const sp<DataSource> &source, String8 *mimeType, float *confidence,
+        sp<AMessage> *) {
 #if 0
     char header;
     if (source->readAt(0, &header, 1) != 1 || header != 0x47) {