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Commit 293e03d8 authored by Jason Simmons's avatar Jason Simmons
Browse files

In the MP3 extractor, compute timestamps based on sample count instead of byte count. 

This fixes timestamp accuracy on VBR streams.

Change-Id: I73a30309536919cbeb5e5163f2f1340e2b9fa4b1
parent 62c1a92d

media/libstagefright/MP3Extractor.cpp

+34 −4
Original line number Diff line number Diff line
@@ -48,7 +48,7 @@ static const uint32_t kMask = 0xfffe0c00; 
bool MP3Extractor::get_mp3_frame_size(

        uint32_t header, size_t *frame_size,

        int *out_sampling_rate, int *out_channels,

        int *out_bitrate) {

        int *out_bitrate, int *out_num_samples) {

    *frame_size = 0;



    if (out_sampling_rate) {
@@ -63,6 +63,10 @@ bool MP3Extractor::get_mp3_frame_size( 
        *out_bitrate = 0;

    }



    if (out_num_samples) {

        *out_num_samples = 1152;

    }



    if ((header & 0xffe00000) != 0xffe00000) {

        return false;

    }
@@ -127,6 +131,10 @@ bool MP3Extractor::get_mp3_frame_size( 
        }



        *frame_size = (12000 * bitrate / sampling_rate + padding) * 4;



        if (out_num_samples) {

            *out_num_samples = 384;

        }

    } else {

        // layer II or III
@@ -150,10 +158,17 @@ bool MP3Extractor::get_mp3_frame_size( 
            bitrate = (layer == 2 /* L2 */)

                ? kBitrateV1L2[bitrate_index - 1]

                : kBitrateV1L3[bitrate_index - 1];



            if (out_num_samples) {

                *out_num_samples = 1152;

            }

        } else {

            // V2 (or 2.5)



            bitrate = kBitrateV2[bitrate_index - 1];

            if (out_num_samples) {

                *out_num_samples = 576;

            }

        }



        if (out_bitrate) {
@@ -374,6 +389,9 @@ private: 
    sp<MP3Seeker> mSeeker;

    MediaBufferGroup *mGroup;



    int64_t mBasisTimeUs;

    int64_t mSamplesRead;



    MP3Source(const MP3Source &);

    MP3Source &operator=(const MP3Source &);

};
@@ -489,7 +507,9 @@ MP3Source::MP3Source( 
      mCurrentTimeUs(0),

      mStarted(false),

      mSeeker(seeker),

      mGroup(NULL) {

      mGroup(NULL),

      mBasisTimeUs(0),

      mSamplesRead(0) {

}



MP3Source::~MP3Source() {
@@ -509,6 +529,9 @@ status_t MP3Source::start(MetaData *) { 
    mCurrentPos = mFirstFramePos;

    mCurrentTimeUs = 0;



    mBasisTimeUs = mCurrentTimeUs;

    mSamplesRead = 0;



    mStarted = true;



    return OK;
@@ -552,6 +575,9 @@ status_t MP3Source::read( 
        } else {

            mCurrentTimeUs = actualSeekTimeUs;

        }



        mBasisTimeUs = mCurrentTimeUs;

        mSamplesRead = 0;

    }



    MediaBuffer *buffer;
@@ -562,6 +588,8 @@ status_t MP3Source::read( 


    size_t frame_size;

    int bitrate;

    int num_samples;

    int sample_rate;

    for (;;) {

        ssize_t n = mDataSource->readAt(mCurrentPos, buffer->data(), 4);

        if (n < 4) {
@@ -575,7 +603,7 @@ status_t MP3Source::read( 


        if ((header & kMask) == (mFixedHeader & kMask)

            && MP3Extractor::get_mp3_frame_size(

                header, &frame_size, NULL, NULL, &bitrate)) {

                header, &frame_size, &sample_rate, NULL, &bitrate, &num_samples)) {

            break;

        }
@@ -613,7 +641,9 @@ status_t MP3Source::read( 
    buffer->meta_data()->setInt32(kKeyIsSyncFrame, 1);



    mCurrentPos += frame_size;

    mCurrentTimeUs += frame_size * 8000ll / bitrate;



    mSamplesRead += num_samples;

    mCurrentTimeUs = mBasisTimeUs + ((mSamplesRead * 1000000) / sample_rate);



    *out = buffer;

media/libstagefright/include/MP3Extractor.h

+1 −1
Original line number Diff line number Diff line
@@ -42,7 +42,7 @@ public: 
    static bool get_mp3_frame_size(

            uint32_t header, size_t *frame_size,

            int *out_sampling_rate = NULL, int *out_channels = NULL,

            int *out_bitrate = NULL);

            int *out_bitrate = NULL, int *out_num_samples = NULL);



private:

    status_t mInitCheck;