diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/xine-engine/metronom.h | 49 |
1 files changed, 45 insertions, 4 deletions
diff --git a/src/xine-engine/metronom.h b/src/xine-engine/metronom.h index 22b02f892..1fc00c240 100644 --- a/src/xine-engine/metronom.h +++ b/src/xine-engine/metronom.h @@ -17,7 +17,7 @@ * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA * - * $Id: metronom.h,v 1.14 2001/11/13 21:47:59 heikos Exp $ + * $Id: metronom.h,v 1.15 2001/12/22 20:16:49 miguelfreitas Exp $ * * metronom: general pts => virtual calculation/assoc * @@ -26,6 +26,18 @@ * video/audio frame with same pts also have same vpts * but pts is likely to differ from vpts * + * the basic idea is: + * video_pts + video_wrap_offset = video_vpts + * audio_pts + audio_wrap_offset = audio_vpts + * + * - video_wrap_offset should be equal to audio_wrap_offset as to have + * perfect audio and video sync. They will differ on brief periods due + * discontinuity correction. + * - metronom should also interpolate vpts values most of the time as + * video_pts and audio_vpts are not given for every frame. + * - corrections to the frame rate may be needed to cope with bad + * encoded streams. + * */ #ifndef HAVE_METRONOM_H @@ -46,6 +58,8 @@ struct metronom_s { /* * this is called to tell metronom to prepare for a new video stream + * (video and audio decoder threads may be blocked at these functions + * to synchronize starting and stopping) */ void (*video_stream_start) (metronom_t *this); @@ -53,6 +67,8 @@ struct metronom_s { /* * this is called to tell metronom to prepare for a new audio stream + * (video and audio decoder threads may be blocked at these functions + * to synchronize starting and stopping) */ void (*audio_stream_start) (metronom_t *this); @@ -85,8 +101,11 @@ struct metronom_s { * parameter pts: pts for frame if known, 0 otherwise * scr: system clock reference, may be 0 or == pts if unknown * - * return value: virtual pts for frame + * return value: virtual pts for frame (interpolated if pts == 0) * + * this function will also update video_wrap_offset if a discontinuity + * is detected (read the comentaries below about discontinuities). + * */ uint32_t (*got_video_frame) (metronom_t *this, uint32_t pts, uint32_t scr); @@ -100,6 +119,9 @@ struct metronom_s { * * return value: virtual pts for audio data * + * this function will also update audio_wrap_offset if a discontinuity + * is detected (read the comentaries below about discontinuities). + * */ uint32_t (*got_audio_samples) (metronom_t *this, uint32_t pts, uint32_t nsamples, uint32_t scr); @@ -111,20 +133,39 @@ struct metronom_s { * scr : system clock reference, may be 0 or == pts if unknown * * return value: virtual pts for SPU packet - * + * (this is the only pts to vpts function that cannot update the wrap_offset + * due to the lack of regularity on spu packets) */ uint32_t (*got_spu_packet) (metronom_t *this, uint32_t pts, uint32_t duration, uint32_t scr); /* - * tell metronom about discontinuities + * Tell metronom about discontinuities. + * + * These functions are called due to a discontinuity detected at + * demux stage from SCR values. As SCR are not guarateed to happen with + * any regularity, we can not correct the xxx_wrap_offset right now. + * + * We will instead prepare both audio and video to correct the + * discontinuity at the first new PTS value (got_video_frame or + * got_audio_samples). As we can predict with reasonably accuracy what + * the old PTS would have being the calculated wrap_offset should be + * good. + * + * (the time between discontinuity is detected to where it is corrected + * may be called "discontinuity window". Inside this window we cannot + * use the xxx_wrap_offset for any pts -> vpts calculation as the result + * would be wrong. The vpts values will be predicted for pts == 0 and + * whenever we get a new pts we can calculate the new xxx_wrap_offset) + * */ void (*expect_audio_discontinuity) (metronom_t *this); void (*expect_video_discontinuity) (metronom_t *this); /* * manually correct audio <-> video sync + * (this constant value is added to video vpts) */ void (*set_av_offset) (metronom_t *this, int32_t pts); |