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Commit f9d87cc8 authored by Robert Shih's avatar Robert Shih
Browse files

Speed up id3v2 unsynchronization 

Instead of doing many overlapping memmoves, do a single copy pass
that skips over the inserted unsynchronization bytes. For some
files this reduces parsing time from minutes to milliseconds.

Similar to commit 72a43b68 but for v2.2 and v2.3.

Bug: 78029004
Test: poc
Change-Id: I735b7051e77a093d86fb7a3e46209875946225ed
parent b9d06b64

media/libstagefright/id3/ID3.cpp

+17 −4
Original line number Diff line number Diff line
@@ -328,12 +328,25 @@ struct id3_header { 
}



void ID3::removeUnsynchronization() {

    for (size_t i = 0; i + 1 < mSize; ++i) {

        if (mData[i] == 0xff && mData[i + 1] == 0x00) {

            memmove(&mData[i + 1], &mData[i + 2], mSize - i - 2);

            --mSize;



    // This file has "unsynchronization", so we have to replace occurrences

    // of 0xff 0x00 with just 0xff in order to get the real data.



    size_t writeOffset = 1;

    for (size_t readOffset = 1; readOffset < mSize; ++readOffset) {

        if (mData[readOffset - 1] == 0xff && mData[readOffset] == 0x00) {

            continue;

        }

        // Only move data if there's actually something to move.

        // This handles the special case of the data being only [0xff, 0x00]

        // which should be converted to just 0xff if unsynchronization is on.

        mData[writeOffset++] = mData[readOffset];

    }



    if (writeOffset < mSize) {

        mSize = writeOffset;

    }



}



static void WriteSyncsafeInteger(uint8_t *dst, size_t x) {