From db6222212528637d8f2afa7f49fc3c8c915bafbe Mon Sep 17 00:00:00 2001
From: Andreas Huber <andih@google.com>
Date: Tue, 28 Sep 2010 09:16:21 -0700
Subject: Vorbis files may have more samples encoded that should be used, i.e.
 we have to trim samples at the end of the stream. This is crucial for proper
 looping of some audio files.

related-to-bug: 3036592
Change-Id: Ib142b171c829ed74156c0281d9d4543fcc96c802
---
 media/libstagefright/OggExtractor.cpp | 77 +++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)

(limited to 'media/libstagefright/OggExtractor.cpp')

diff --git a/media/libstagefright/OggExtractor.cpp b/media/libstagefright/OggExtractor.cpp
index 7a8cf32..43938b2 100644
--- a/media/libstagefright/OggExtractor.cpp
+++ b/media/libstagefright/OggExtractor.cpp
@@ -93,7 +93,10 @@ private:
     sp<DataSource> mSource;
     off_t mOffset;
     Page mCurrentPage;
+    uint64_t mPrevGranulePosition;
     size_t mCurrentPageSize;
+    bool mFirstPacketInPage;
+    uint64_t mCurrentPageSamples;
     size_t mNextLaceIndex;
 
     off_t mFirstDataOffset;
@@ -113,6 +116,8 @@ private:
     void parseFileMetaData();
     void extractAlbumArt(const void *data, size_t size);
 
+    uint64_t findPrevGranulePosition(off_t pageOffset);
+
     MyVorbisExtractor(const MyVorbisExtractor &);
     MyVorbisExtractor &operator=(const MyVorbisExtractor &);
 };
@@ -193,7 +198,10 @@ status_t OggSource::read(
 MyVorbisExtractor::MyVorbisExtractor(const sp<DataSource> &source)
     : mSource(source),
       mOffset(0),
+      mPrevGranulePosition(0),
       mCurrentPageSize(0),
+      mFirstPacketInPage(true),
+      mCurrentPageSamples(0),
       mNextLaceIndex(0),
       mFirstDataOffset(-1) {
     mCurrentPage.mNumSegments = 0;
@@ -238,6 +246,52 @@ status_t MyVorbisExtractor::findNextPage(
     }
 }
 
+// Given the offset of the "current" page, find the page immediately preceding
+// it (if any) and return its granule position.
+// To do this we back up from the "current" page's offset until we find any
+// page preceding it and then scan forward to just before the current page.
+uint64_t MyVorbisExtractor::findPrevGranulePosition(off_t pageOffset) {
+    off_t prevPageOffset = 0;
+    off_t prevGuess = pageOffset;
+    for (;;) {
+        if (prevGuess >= 5000) {
+            prevGuess -= 5000;
+        } else {
+            prevGuess = 0;
+        }
+
+        LOGV("backing up %ld bytes", pageOffset - prevGuess);
+
+        CHECK_EQ(findNextPage(prevGuess, &prevPageOffset), (status_t)OK);
+
+        if (prevPageOffset < pageOffset || prevGuess == 0) {
+            break;
+        }
+    }
+
+    if (prevPageOffset == pageOffset) {
+        // We did not find a page preceding this one.
+        return 0;
+    }
+
+    LOGV("prevPageOffset at %ld, pageOffset at %ld", prevPageOffset, pageOffset);
+
+    for (;;) {
+        Page prevPage;
+        ssize_t n = readPage(prevPageOffset, &prevPage);
+
+        if (n <= 0) {
+            return 0;
+        }
+
+        prevPageOffset += n;
+
+        if (prevPageOffset == pageOffset) {
+            return prevPage.mGranulePosition;
+        }
+    }
+}
+
 status_t MyVorbisExtractor::seekToOffset(off_t offset) {
     if (mFirstDataOffset >= 0 && offset < mFirstDataOffset) {
         // Once we know where the actual audio data starts (past the headers)
@@ -252,9 +306,16 @@ status_t MyVorbisExtractor::seekToOffset(off_t offset) {
         return err;
     }
 
+    // We found the page we wanted to seek to, but we'll also need
+    // the page preceding it to determine how many valid samples are on
+    // this page.
+    mPrevGranulePosition = findPrevGranulePosition(pageOffset);
+
     mOffset = pageOffset;
 
     mCurrentPageSize = 0;
+    mFirstPacketInPage = true;
+    mCurrentPageSamples = 0;
     mCurrentPage.mNumSegments = 0;
     mNextLaceIndex = 0;
 
@@ -399,6 +460,12 @@ status_t MyVorbisExtractor::readNextPacket(MediaBuffer **out) {
                     buffer->meta_data()->setInt64(kKeyTime, timeUs);
                 }
 
+                if (mFirstPacketInPage) {
+                    buffer->meta_data()->setInt32(
+                            kKeyValidSamples, mCurrentPageSamples);
+                    mFirstPacketInPage = false;
+                }
+
                 *out = buffer;
 
                 return OK;
@@ -423,6 +490,12 @@ status_t MyVorbisExtractor::readNextPacket(MediaBuffer **out) {
             return n < 0 ? n : (status_t)ERROR_END_OF_STREAM;
         }
 
+        mCurrentPageSamples =
+            mCurrentPage.mGranulePosition - mPrevGranulePosition;
+        mFirstPacketInPage = true;
+
+        mPrevGranulePosition = mCurrentPage.mGranulePosition;
+
         mCurrentPageSize = n;
         mNextLaceIndex = 0;
 
@@ -435,6 +508,10 @@ status_t MyVorbisExtractor::readNextPacket(MediaBuffer **out) {
                     buffer->meta_data()->setInt64(kKeyTime, timeUs);
                 }
 
+                buffer->meta_data()->setInt32(
+                        kKeyValidSamples, mCurrentPageSamples);
+                mFirstPacketInPage = false;
+
                 *out = buffer;
 
                 return OK;
-- 
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