The subtraction -4180 is the same as audioTimestampStep; For video , it did the same subtraction as well using the videoTimestampStep

static const int videoTimestampStep = 3003;       // Value based on pmfplayer (mpegTimestampPerSecond / 29.970 (fps)).
static const int audioTimestampStep = 4180;       // For audio play at 44100 Hz (2048 samples / 44100 * mpegTimestampPerSecond == 4180)