set_clock_at     1416 ffplay.c           set_clock_at(c, pts, serial, time);
set_clock_at     2568 ffplay.c               set_clock_at(&is->audclk, is->audio_clock - (double)(2 * is->audio_hw_buf_size + is->audio_write_buf_size) / is->audio_tgt.bytes_per_sec, is->audio_clock_serial, audio_callback_time / 1000000.0);