We don't support mid-stream format changes

    if (mWriteHeader.sample_rate != getSampleRate() ||

        mWriteHeader.channels != getChannels() ||

        mWriteHeader.bits_per_sample != getBitsPerSample()) {

        ALOGE("FLACParser::readBuffer write changed parameters mid-stream");

        ALOGE("FLACParser::readBuffer write changed parameters mid-stream: %d/%d/%d -> %d/%d/%d",

                getSampleRate(), getChannels(), getBitsPerSample(),

                mWriteHeader.sample_rate, mWriteHeader.channels, mWriteHeader.bits_per_sample);

        return NULL;

    }

    // acquire a media buffer

    CHECK(mGroup != NULL);