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vlc/modules/codec/synchro.c

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/*****************************************************************************
* synchro.c : frame dropping routines
*****************************************************************************
* Copyright (C) 1999-2005 VLC authors and VideoLAN
*
* Authors: Christophe Massiot <massiot@via.ecp.fr>
* Samuel Hocevar <sam@via.ecp.fr>
* Jean-Marc Dressler <polux@via.ecp.fr>
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program; if not, write to the Free Software Foundation,
* Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
*****************************************************************************/
/*
* DISCUSSION : How to Write an efficient Frame-Dropping Algorithm
* ==========
*
* This implementation is based on mathematical and statistical
* developments. Older implementations used an enslavement, considering
* that if we're late when reading an I picture, we will decode one frame
* less. It had a tendency to derive, and wasn't responsive enough, which
* would have caused trouble with the stream control stuff.
*
* 1. Structure of a picture stream
* =============================
* Between 2 I's, we have for instance :
* I B P B P B P B P B P B I
* t0 t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 t11 t12
* Please bear in mind that B's and IP's will be inverted when displaying
* (decoding order != presentation order). Thus, t1 < t0.
*
* 2. Definitions
* ===========
* t[0..12] : Presentation timestamps of pictures 0..12.
* t : Current timestamp, at the moment of the decoding.
* T : Picture period, T = 1/frame_rate.
* tau[I,P,B] : Mean time to decode an [I,P,B] picture.
* tauYUV : Mean time to render a picture (given by the video_output).
* tau´[I,P,B] = 2 * tau[I,P,B] + tauYUV
* : Mean time + typical difference (estimated to tau/2, that
* needs to be confirmed) + render time.
* DELTA : A given error margin.
*
* 3. General considerations
* ======================
* We define three types of machines :
* 14T > tauI : machines capable of decoding all I pictures
* 2T > tauP : machines capable of decoding all P pictures
* T > tauB : machines capable of decoding all B pictures
*
* 4. Decoding of an I picture
* ========================
* On fast machines, we decode all I's.
* Otherwise :
* We can decode an I picture if we simply have enough time to decode it
* before displaying :
* t0 - t > tau´I + DELTA
*
* 5. Decoding of a P picture
* =======================
* On fast machines, we decode all P's.
* Otherwise :
* First criterion : have time to decode it.
* t2 - t > tau´P + DELTA
*
* Second criterion : it shouldn't prevent us from displaying the forthcoming
* I picture, which is more important.
* t12 - t > tau´P + tau´I + DELTA
*
* 6. Decoding of a B picture
* =======================
* On fast machines, we decode all B's. Otherwise :
* t1 - t > tau´B + DELTA
* Since the next displayed I or P is already decoded, we don't have to
* worry about it.
*
* I hope you will have a pleasant flight and do not forget your life
* jacket.
* --Meuuh (2000-12-29)
*/
/*****************************************************************************
* Preamble
*****************************************************************************/
#ifdef HAVE_CONFIG_H
# include "config.h"
#endif
#include <vlc_common.h>
#include <vlc_codec.h>
#include "synchro.h"
/*
* Logging helpers
*/
/**
* Print a debug log message if not silenced
* using the `quiet-synchro` option
*/
#define synchro_msg_Dbg(p_this, ...) do { \
if( !p_this->b_quiet ) \
msg_Generic(p_this->p_dec, VLC_MSG_DBG, __VA_ARGS__); \
} while (0)
/**
* Print a warning log message if not silenced
* using the `quiet-synchro` option
*/
#define synchro_msg_Warn(p_this, ...) do { \
if( !p_this->b_quiet ) \
msg_Generic(p_this->p_dec, VLC_MSG_WARN, __VA_ARGS__); \
} while (0)
/*
* Local prototypes
*/
#define MAX_PIC_AVERAGE 8
struct decoder_synchro_t
{
/* */
decoder_t *p_dec;
/* */
int i_frame_rate;
bool b_no_skip;
bool b_quiet;
/* date of the beginning of the decoding of the current picture */
vlc_tick_t decoding_start;
/* stream properties */
unsigned int i_n_p, i_n_b;
/* decoding values */
vlc_tick_t p_tau[4]; /* average decoding durations */
unsigned int pi_meaningful[4]; /* number of durations read */
/* render_time filled by SynchroChoose() */
vlc_tick_t i_render_time;
/* stream context */
int i_nb_ref; /* Number of reference pictures */
int i_dec_nb_ref; /* Number of reference pictures we'll *
* have if we decode the current pic */
int i_trash_nb_ref; /* Number of reference pictures we'll *
* have if we trash the current pic */
unsigned int i_eta_p, i_eta_b;
vlc_tick_t backward_pts, current_pts;
int i_current_period; /* period to add to the next picture */
int i_backward_period; /* period to add after the next
* reference picture
* (backward_period * period / 2) */
/* statistics */
unsigned int i_trashed_pic, i_not_chosen_pic, i_pic;
};
/* Error margins */
#define DELTA VLC_TICK_FROM_MS(75) /* 3s/40 */
#define MAX_VALID_TAU VLC_TICK_FROM_MS(300)
#define DEFAULT_NB_P 5
#define DEFAULT_NB_B 1
/*****************************************************************************
* decoder_SynchroInit : You know what ?
*****************************************************************************/
decoder_synchro_t * decoder_SynchroInit( decoder_t *p_dec, int i_frame_rate )
{
decoder_synchro_t * p_synchro = calloc( 1, sizeof(*p_synchro) );
if( !p_synchro )
return NULL;
p_synchro->p_dec = p_dec;
p_synchro->b_no_skip = !var_InheritBool( p_dec, "skip-frames" );
p_synchro->b_quiet = var_InheritBool( p_dec, "quiet-synchro" );
/* We use a fake stream pattern, which is often right. */
p_synchro->i_n_p = p_synchro->i_eta_p = DEFAULT_NB_P;
p_synchro->i_n_b = p_synchro->i_eta_b = DEFAULT_NB_B;
memset( p_synchro->p_tau, 0, 4 * sizeof(vlc_tick_t) );
memset( p_synchro->pi_meaningful, 0, 4 * sizeof(unsigned int) );
p_synchro->i_nb_ref = 0;
p_synchro->i_trash_nb_ref = p_synchro->i_dec_nb_ref = 0;
p_synchro->current_pts = 1,
p_synchro->backward_pts = VLC_TICK_INVALID;
p_synchro->i_current_period = p_synchro->i_backward_period = 0;
p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic =
p_synchro->i_pic = 0;
p_synchro->i_frame_rate = i_frame_rate;
return p_synchro;
}
/*****************************************************************************
* decoder_SynchroRelease : You know what ?
*****************************************************************************/
void decoder_SynchroRelease( decoder_synchro_t * p_synchro )
{
free( p_synchro );
}
/*****************************************************************************
* decoder_SynchroReset : Reset the reference picture counter
*****************************************************************************/
void decoder_SynchroReset( decoder_synchro_t * p_synchro )
{
p_synchro->i_nb_ref = 0;
p_synchro->i_trash_nb_ref = p_synchro->i_dec_nb_ref = 0;
}
/*****************************************************************************
* decoder_SynchroChoose : Decide whether we will decode a picture or not
*****************************************************************************/
bool decoder_SynchroChoose( decoder_synchro_t * p_synchro, int i_coding_type,
vlc_tick_t i_render_time, bool b_low_delay )
{
#define TAU_PRIME( coding_type ) (p_synchro->p_tau[(coding_type)] \
+ (p_synchro->p_tau[(coding_type)] >> 1) \
+ p_synchro->i_render_time)
#define S (*p_synchro)
vlc_tick_t now, period;
vlc_tick_t pts;
bool b_decode = 0;
float i_current_rate;
if ( p_synchro->b_no_skip )
return 1;
i_current_rate = decoder_GetDisplayRate( p_synchro->p_dec );
now = vlc_tick_now();
period = vlc_tick_from_samples(1001, p_synchro->i_frame_rate) * i_current_rate;
p_synchro->i_render_time = i_render_time;
switch( i_coding_type )
{
case I_CODING_TYPE:
if( b_low_delay )
{
pts = decoder_GetDisplayDate( p_synchro->p_dec, now, S.current_pts );
}
else if( S.backward_pts != VLC_TICK_INVALID )
{
pts = decoder_GetDisplayDate( p_synchro->p_dec, now, S.backward_pts );
}
else
{
/* displaying order : B B P B B I
* ^ ^
* | +- current picture
* +- current PTS
*/
pts = decoder_GetDisplayDate( p_synchro->p_dec, now, S.current_pts ) + period * (S.i_n_b + 2);
}
if( (1 + S.i_n_p * (S.i_n_b + 1)) * period > S.p_tau[I_CODING_TYPE] )
{
b_decode = 1;
}
else
{
b_decode = (pts - now) > (TAU_PRIME(I_CODING_TYPE) + DELTA);
}
if( pts == VLC_TICK_INVALID )
b_decode = 1;
if( !b_decode )
{
synchro_msg_Warn( p_synchro,
"synchro trashing I (%"PRId64")", pts - now );
}
break;
case P_CODING_TYPE:
if( b_low_delay )
{
pts = decoder_GetDisplayDate( p_synchro->p_dec, now, S.current_pts );
}
else if( S.backward_pts != VLC_TICK_INVALID )
{
pts = decoder_GetDisplayDate( p_synchro->p_dec, now, S.backward_pts );
}
else
{
pts = decoder_GetDisplayDate( p_synchro->p_dec, now, S.current_pts + period * (S.i_n_b + 1) );
}
if( p_synchro->i_nb_ref < 1 )
{
b_decode = 0;
}
else if( (1 + S.i_n_p * (S.i_n_b + 1)) * period >
S.p_tau[I_CODING_TYPE] )
{
if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
{
/* Security in case we're _really_ late */
b_decode = (pts - now > 0);
}
else
{
b_decode = (pts - now) > (TAU_PRIME(P_CODING_TYPE) + DELTA);
/* next I */
b_decode &= (pts - now
+ period
* ( (S.i_n_p - S.i_eta_p) * (1 + S.i_n_b) - 1 ))
> (TAU_PRIME(P_CODING_TYPE)
+ TAU_PRIME(I_CODING_TYPE) + DELTA);
}
}
else
{
b_decode = 0;
}
if( p_synchro->i_nb_ref >= 1 && pts == VLC_TICK_INVALID )
b_decode = 1;
break;
case B_CODING_TYPE:
pts = decoder_GetDisplayDate( p_synchro->p_dec, now, S.current_pts );
if( p_synchro->i_nb_ref < 2 )
{
b_decode = 0;
}
else if( (S.i_n_b + 1) * period > S.p_tau[P_CODING_TYPE] )
{
b_decode = (pts - now) > (TAU_PRIME(B_CODING_TYPE) + DELTA);
}
else
{
b_decode = 0;
}
if( p_synchro->i_nb_ref >= 2 && pts == VLC_TICK_INVALID )
b_decode = 1;
break;
}
if( !b_decode )
{
S.i_not_chosen_pic++;
}
return( b_decode );
#undef S
#undef TAU_PRIME
}
/*****************************************************************************
* decoder_SynchroTrash : Update counters when we trash a picture
*****************************************************************************/
void decoder_SynchroTrash( decoder_synchro_t * p_synchro )
{
p_synchro->i_trashed_pic++;
p_synchro->i_nb_ref = p_synchro->i_trash_nb_ref;
}
/*****************************************************************************
* decoder_SynchroDecode : Update timers when we decide to decode a picture
*****************************************************************************/
void decoder_SynchroDecode( decoder_synchro_t * p_synchro )
{
p_synchro->decoding_start = vlc_tick_now();
p_synchro->i_nb_ref = p_synchro->i_dec_nb_ref;
}
/*****************************************************************************
* decoder_SynchroEnd : Called when the image is totally decoded
*****************************************************************************/
void decoder_SynchroEnd( decoder_synchro_t * p_synchro, int i_coding_type,
bool b_garbage )
{
vlc_tick_t tau;
if( b_garbage )
return;
tau = vlc_tick_now() - p_synchro->decoding_start;
/* If duration too high, something happened (pause ?), so don't
* take it into account. */
if( tau < 3 * p_synchro->p_tau[i_coding_type] ||
( !p_synchro->pi_meaningful[i_coding_type] && tau < MAX_VALID_TAU ) )
{
/* Mean with average tau, to ensure stability. */
p_synchro->p_tau[i_coding_type] =
(p_synchro->pi_meaningful[i_coding_type]
* p_synchro->p_tau[i_coding_type] + tau)
/ (p_synchro->pi_meaningful[i_coding_type] + 1);
if( p_synchro->pi_meaningful[i_coding_type] < MAX_PIC_AVERAGE )
{
p_synchro->pi_meaningful[i_coding_type]++;
}
}
}
/*****************************************************************************
* decoder_SynchroDate : When an image has been decoded, ask for its date
*****************************************************************************/
vlc_tick_t decoder_SynchroDate( decoder_synchro_t * p_synchro )
{
/* No need to lock, since PTS are only used by the video parser. */
return p_synchro->current_pts;
}
/*****************************************************************************
* decoder_SynchroNewPicture: Update stream structure and PTS
*****************************************************************************/
void decoder_SynchroNewPicture( decoder_synchro_t * p_synchro, int i_coding_type,
int i_repeat_field, vlc_tick_t next_pts,
vlc_tick_t next_dts, bool b_low_delay )
{
vlc_tick_t period = vlc_tick_from_samples(1001, p_synchro->i_frame_rate);
#if 0
vlc_tick_t now = vlc_tick_now();
#endif
switch( i_coding_type )
{
case I_CODING_TYPE:
if( p_synchro->i_eta_p && p_synchro->i_eta_p != p_synchro->i_n_p )
{
#if 0
synchro_msg_Dbg( p_synchro,
"stream periodicity changed from P[%d] to P[%d]",
p_synchro->i_n_p, p_synchro->i_eta_p );
#endif
p_synchro->i_n_p = p_synchro->i_eta_p;
}
p_synchro->i_eta_p = p_synchro->i_eta_b = 0;
p_synchro->i_trash_nb_ref = 0;
if( p_synchro->i_nb_ref < 2 )
p_synchro->i_dec_nb_ref = p_synchro->i_nb_ref + 1;
else
p_synchro->i_dec_nb_ref = p_synchro->i_nb_ref;
#if 0
synchro_msg_Dbg( p_synchro, "I(%"PRId64") P(%"PRId64")[%d] B(%"PRId64")"
"[%d] YUV(%"PRId64") : trashed %d:%d/%d",
p_synchro->p_tau[I_CODING_TYPE],
p_synchro->p_tau[P_CODING_TYPE],
p_synchro->i_n_p,
p_synchro->p_tau[B_CODING_TYPE],
p_synchro->i_n_b,
p_synchro->i_render_time,
p_synchro->i_not_chosen_pic,
p_synchro->i_trashed_pic -
p_synchro->i_not_chosen_pic,
p_synchro->i_pic );
p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic
= p_synchro->i_pic = 0;
#else
if( p_synchro->i_pic >= 100 )
{
if( p_synchro->i_trashed_pic != 0 )
synchro_msg_Dbg( p_synchro, "decoded %d/%d pictures",
p_synchro->i_pic
- p_synchro->i_trashed_pic,
p_synchro->i_pic );
p_synchro->i_trashed_pic = p_synchro->i_not_chosen_pic
= p_synchro->i_pic = 0;
}
#endif
break;
case P_CODING_TYPE:
p_synchro->i_eta_p++;
if( p_synchro->i_eta_b
&& p_synchro->i_eta_b != p_synchro->i_n_b )
{
#if 0
synchro_msg_Dbg( p_synchro,
"stream periodicity changed from B[%d] to B[%d]",
p_synchro->i_n_b, p_synchro->i_eta_b );
#endif
p_synchro->i_n_b = p_synchro->i_eta_b;
}
p_synchro->i_eta_b = 0;
p_synchro->i_dec_nb_ref = 2;
p_synchro->i_trash_nb_ref = 0;
break;
case B_CODING_TYPE:
p_synchro->i_eta_b++;
p_synchro->i_dec_nb_ref = p_synchro->i_trash_nb_ref
= p_synchro->i_nb_ref;
break;
}
p_synchro->current_pts += p_synchro->i_current_period
* (period >> 1);
#define PTS_THRESHOLD (period >> 2)
if( i_coding_type == B_CODING_TYPE || b_low_delay )
{
/* A video frame can be displayed 1, 2 or 3 times, according to
* repeat_first_field, top_field_first, progressive_sequence and
* progressive_frame. */
p_synchro->i_current_period = i_repeat_field;
if( next_pts != VLC_TICK_INVALID )
{
if( next_pts - p_synchro->current_pts
> PTS_THRESHOLD
|| p_synchro->current_pts - next_pts
> PTS_THRESHOLD )
{
synchro_msg_Warn( p_synchro, "decoder synchro warning: pts != "
"current_date (%"PRId64")",
p_synchro->current_pts
- next_pts );
}
p_synchro->current_pts = next_pts;
}
}
else
{
p_synchro->i_current_period = p_synchro->i_backward_period;
p_synchro->i_backward_period = i_repeat_field;
if( p_synchro->backward_pts != VLC_TICK_INVALID )
{
if( next_dts != VLC_TICK_INVALID &&
(next_dts - p_synchro->backward_pts
> PTS_THRESHOLD
|| p_synchro->backward_pts - next_dts
> PTS_THRESHOLD) )
{
synchro_msg_Warn( p_synchro, "backward_pts != dts (%"PRId64")",
next_dts
- p_synchro->backward_pts );
}
if( p_synchro->backward_pts - p_synchro->current_pts
> PTS_THRESHOLD
|| p_synchro->current_pts - p_synchro->backward_pts
> PTS_THRESHOLD )
{
synchro_msg_Warn( p_synchro,
"backward_pts != current_pts (%"PRId64")",
p_synchro->current_pts
- p_synchro->backward_pts );
}
p_synchro->current_pts = p_synchro->backward_pts;
p_synchro->backward_pts = VLC_TICK_INVALID;
}
else if( next_dts != VLC_TICK_INVALID )
{
if( next_dts - p_synchro->current_pts
> PTS_THRESHOLD
|| p_synchro->current_pts - next_dts
> PTS_THRESHOLD )
{
synchro_msg_Warn( p_synchro, "dts != current_pts (%"PRId64")",
p_synchro->current_pts
- next_dts );
}
/* By definition of a DTS. */
p_synchro->current_pts = next_dts;
}
if( next_pts != VLC_TICK_INVALID )
{
/* Store the PTS for the next time we have to date an I picture. */
p_synchro->backward_pts = next_pts;
}
}
#undef PTS_THRESHOLD
#if 0
/* Removed for incompatibility with slow motion */
if( p_synchro->current_pts + DEFAULT_PTS_DELAY < now )
{
/* We cannot be _that_ late, something must have happened, reinit
* the dates. */
synchro_msg_Warn( p_synchro, "PTS << now (%"PRId64"), resetting",
now - p_synchro->current_pts - DEFAULT_PTS_DELAY );
p_synchro->current_pts = now + DEFAULT_PTS_DELAY;
}
if( p_synchro->backward_pts != VLC_TICK_INVALID
&& p_synchro->backward_pts + DEFAULT_PTS_DELAY < now )
{
/* The same. */
p_synchro->backward_pts = VLC_TICK_INVALID;
}
#endif
p_synchro->i_pic++;
}