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Commit 59fe406b authored by Jean-Michel Trivi's avatar Jean-Michel Trivi
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Bug 5156756 Fix AAC ADTS header size computation 

This previous frame size computation code had two incorrect
 assumptions:
 1/ the ADTS frame length value already contains the header size
 2/ the ADTS header is not of fixed size: it is 2 bytes bigger
  if it contains the CRC value.
For 1/, the code worked because when the header size was added
 to the frame size, the + operator is of stronger precedence
 than the ? operator, so the size added was always 0 (instead
 of ADTS_HEADER_LENGTH.
For 2/, the code worked as long as there was no CRC in the ADTS
 data.

The fix consists in:
 - documenting what the frame length computation code returns
 - fixing the frame length computation
 - when computing the frame length, also returning the header
  size so the correct data can be sent to the decoder.

Change-Id: I92df72a9e531f594f762e63d62f9dee7b0109904
parent 890be6b9

media/libstagefright/AACExtractor.cpp

+24 −9
Original line number Diff line number Diff line
@@ -33,8 +33,6 @@ 


namespace android {



#define ADTS_HEADER_LENGTH 7



class AACSource : public MediaSource {

public:

    AACSource(const sp<DataSource> &source,
@@ -88,7 +86,16 @@ uint32_t get_sample_rate(const uint8_t sf_index) 
    return 0;

}



static size_t getFrameSize(const sp<DataSource> &source, off64_t offset) {

// Returns the frame length in bytes as described in an ADTS header starting at the given offset,

//     or 0 if the size can't be read due to an error in the header or a read failure.

// The returned value is the AAC frame size with the ADTS header length (regardless of

//     the presence of the CRC).

// If headerSize is non-NULL, it will be used to return the size of the header of this ADTS frame.

static size_t getAdtsFrameLength(const sp<DataSource> &source, off64_t offset, size_t* headerSize) {



    const size_t kAdtsHeaderLengthNoCrc = 7;

    const size_t kAdtsHeaderLengthWithCrc = 9;



    size_t frameSize = 0;



    uint8_t syncword[2];
@@ -111,7 +118,15 @@ static size_t getFrameSize(const sp<DataSource> &source, off64_t offset) { 
    }



    frameSize = (header[0] & 0x3) << 11 | header[1] << 3 | header[2] >> 5;

    frameSize += ADTS_HEADER_LENGTH + protectionAbsent ? 0 : 2;



    // protectionAbsent is 0 if there is CRC

    size_t headSize = protectionAbsent ? kAdtsHeaderLengthNoCrc : kAdtsHeaderLengthWithCrc;

    if (headSize > frameSize) {

        return 0;

    }

    if (headerSize != NULL) {

        *headerSize = headSize;

    }



    return frameSize;

}
@@ -148,7 +163,7 @@ AACExtractor::AACExtractor(const sp<DataSource> &source) 


    if (mDataSource->getSize(&streamSize) == OK) {

         while (offset < streamSize) {

            if ((frameSize = getFrameSize(source, offset)) == 0) {

            if ((frameSize = getAdtsFrameLength(source, offset, NULL)) == 0) {

                return;

            }
@@ -268,8 +283,8 @@ status_t AACSource::read( 
        }

    }



    size_t frameSize, frameSizeWithoutHeader;

    if ((frameSize = getFrameSize(mDataSource, mOffset)) == 0) {

    size_t frameSize, frameSizeWithoutHeader, headerSize;

    if ((frameSize = getAdtsFrameLength(mDataSource, mOffset, &headerSize)) == 0) {

        return ERROR_END_OF_STREAM;

    }
@@ -279,8 +294,8 @@ status_t AACSource::read( 
        return err;

    }



    frameSizeWithoutHeader = frameSize - ADTS_HEADER_LENGTH;

    if (mDataSource->readAt(mOffset + ADTS_HEADER_LENGTH, buffer->data(),

    frameSizeWithoutHeader = frameSize - headerSize;

    if (mDataSource->readAt(mOffset + headerSize, buffer->data(),

                frameSizeWithoutHeader) != (ssize_t)frameSizeWithoutHeader) {

        buffer->release();

        buffer = NULL;