Make sure that timestamp does not go backward in MP4 file writer

                // The idea here is to avoid having two or more samples with the

                // same timestamp in the output file.

                if (mTimeScale >= 1000000LL) {

                    timestampUs += 1;

                    timestampUs = lastTimestampUs + 1;

                } else {

                    timestampUs += (1000000LL + (mTimeScale >> 1)) / mTimeScale;

                    timestampUs = lastTimestampUs + (1000000LL + (mTimeScale >> 1)) / mTimeScale;

                }

#endif

            }