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Commit 1b0be545 authored by Gopalakrishnan Nallasamy's avatar Gopalakrishnan Nallasamy
Browse files

MPEG4Writer:Optimize number of write(2) calls 

Instead of making several write(2) calls to pass length of a video buffer,
club them together in an array and call write(2) once. This reduces the
number of system calls to write a buffer length from 4 to 1(default case),
there by avoiding 75% of user/kernel context switches just for this.
At 240 fps, it would be 240 instead of 960 calls.

Bug: 157160851

Test: atest android.media.cts.MediaMuxerTest
Test: atest android.media.cts.MediaRecorderTest
Test: atest android.mediav2.cts.MuxerTest

Change-Id: I7f3c8ecd5f2bccc6c4b87ccd0dc8104f4e98198a
parent e658962c

media/libstagefright/MPEG4Writer.cpp

+10 −14
Original line number Diff line number Diff line
@@ -1506,25 +1506,21 @@ void MPEG4Writer::addMultipleLengthPrefixedSamples_l(MediaBuffer *buffer) { 
void MPEG4Writer::addLengthPrefixedSample_l(MediaBuffer *buffer) {

    size_t length = buffer->range_length();

    if (mUse4ByteNalLength) {

        uint8_t x = length >> 24;

        writeOrPostError(mFd, &x, 1);

        x = (length >> 16) & 0xff;

        writeOrPostError(mFd, &x, 1);

        x = (length >> 8) & 0xff;

        writeOrPostError(mFd, &x, 1);

        x = length & 0xff;

        writeOrPostError(mFd, &x, 1);



        uint8_t x[4];

        x[0] = length >> 24;

        x[1] = (length >> 16) & 0xff;

        x[2] = (length >> 8) & 0xff;

        x[3] = length & 0xff;

        writeOrPostError(mFd, &x, 4);

        writeOrPostError(mFd, (const uint8_t*)buffer->data() + buffer->range_offset(), length);



        mOffset += length + 4;

    } else {

        CHECK_LT(length, 65536u);



        uint8_t x = length >> 8;

        writeOrPostError(mFd, &x, 1);

        x = length & 0xff;

        writeOrPostError(mFd, &x, 1);

        uint8_t x[2];

        x[0] = length >> 8;

        x[1] = length & 0xff;

        writeOrPostError(mFd, &x, 2);

        writeOrPostError(mFd, (const uint8_t*)buffer->data() + buffer->range_offset(), length);

        mOffset += length + 2;

    }