plugin_2pass2.c

这是一个压缩解压包,用C语言进行编程的,里面有详细的源代码.

	if (rc->param.vbv_size > 0)  {
		const double fps = (double)create->fbase/(double)create->fincr;
		int status = check_curve_for_vbv_compliancy(rc, fps);

		if (status) {
			DPRINTF(XVID_DEBUG_RC, "[xvid rc] Underflow detected - Scaling Curve for compliancy.\n");
		}

		status = scale_curve_for_vbv_compliancy(rc, fps);

		if (status == 0) {
			DPRINTF(XVID_DEBUG_RC, "[xvid rc] VBV compliant curve scaling done.\n");
		} else {
			DPRINTF(XVID_DEBUG_RC, "[xvid rc] VBV compliant curve scaling impossible.\n");
		}
	}
	*handle = rc;
	return(0);
}

/*----------------------------------------------------------------------------
 *--------------------------------------------------------------------------*/

static int
rc_2pass2_destroy(rc_2pass2_t * rc, xvid_plg_destroy_t * destroy)
{
	DPRINTF(XVID_DEBUG_RC, "[xvid rc] -- target_total:%lld desired_total:%.2f (%.2f%%) actual_total:%.2f (%.2f%%)\n",
			rc->target,
			rc->desired_total,
			100*rc->desired_total/(double)rc->target,
			rc->real_total,
			100*rc->real_total/(double)rc->target);

	free(rc->keyframe_locations);
	free(rc->stats);
	free(rc);
	return(0);
}

/*----------------------------------------------------------------------------
 *--------------------------------------------------------------------------*/

static int
rc_2pass2_before(rc_2pass2_t * rc, xvid_plg_data_t * data)
{
	twopass_stat_t * s = &rc->stats[data->frame_num];
	double dbytes;
	double scaled_quant;
	double overflow;
	int capped_to_max_framesize = 0;

	/* This function is quite long but easy to understand. In order to simplify
	 * the code path (a bit), we treat 3 cases that can return immediatly. */

	/* First case: Another plugin has already set a quantizer */
	if (data->quant > 0)
		return(0);

	/* Second case: insufficent stats data
	 * We can't guess much what we should do, let core decide all alone */
	if (data->frame_num >= rc->num_frames) {
		DPRINTF(XVID_DEBUG_RC,"[xvid rc] -- stats file too short (now processing frame %d)",
			data->frame_num);
		return(0);
	}

	/* Third case: We are in a Quant zone
	 * Quant zones must just ensure we use the same settings as first pass
	 * So set the quantizer and the type */
	if (s->zone_mode == XVID_ZONE_QUANT) {
		/* Quant stuff */
		rc->fq_error += s->weight;
		data->quant = (int)rc->fq_error;
		rc->fq_error -= data->quant;

		/* The type stuff */
		data->type = s->type;

		/* The only required data for AFTER step is this one for the overflow
		 * control */
		s->desired_length = s->length;

		return(0);
	}


	/*************************************************************************/
	/*************************************************************************/
	/*************************************************************************/

	/*-------------------------------------------------------------------------
	 * Frame bit allocation first part
	 *
	 * First steps apply user settings, just like it is done in the theoritical
	 * scaled_curve_apply_advanced_parameters
	 *-----------------------------------------------------------------------*/

	/* Set desired to what we are wanting to obtain for this frame */
	dbytes = (double)s->scaled_length;

	/* IFrame user settings*/
	if (s->type == XVID_TYPE_IVOP) {
		/* Keyframe boosting -- All keyframes benefit from it */
		dbytes += dbytes*rc->param.keyframe_boost / 100;

#if 0 /* ToDo: decide how to apply kfthresholding */
#endif
	} else {

		/* P/S/B frames must reserve some bits for iframe boosting */
		dbytes *= rc->pb_iboost_tax_ratio;

		/* Apply assymetric curve compression */
		if (rc->param.curve_compression_high || rc->param.curve_compression_low) {
			double assymetric_delta;

			/* Compute the assymetric delta, this is computed before applying
			 * the tax, as done in the pre_process function */
			if (dbytes > rc->avg_length[s->type-1])
				assymetric_delta = (rc->avg_length[s->type-1] - dbytes) * rc->param.curve_compression_high / 100.0;
			else
				assymetric_delta = (rc->avg_length[s->type-1] - dbytes) * rc->param.curve_compression_low  / 100.0;

			/* Now we must apply the assymetric tax, else our curve compression
			 * would not give a theoritical target size equal to what it is
			 * expected */
			dbytes *= rc->assymetric_tax_ratio;

			/* Now we can add the assymetric delta */
			dbytes += assymetric_delta;
		}
	}

	/* That is what we would like to have -- Don't put that chunk after
	 * overflow control, otherwise, overflow is counted twice and you obtain
	 * half sized bitrate sequences */
	s->desired_length  = (int)dbytes;
	rc->desired_total += dbytes;

	/*------------------------------------------------------------------------
	 * Frame bit allocation: overflow control part.
	 *
	 * Unlike the theoritical scaled_curve_apply_advanced_parameters, here
	 * it's real encoding and we need to make sure we don't go so far from
	 * what is our ideal scaled curve.
	 *-----------------------------------------------------------------------*/

	/* Compute the overflow we should compensate */
	if (s->type != XVID_TYPE_IVOP || rc->overflow > 0) {
		double frametype_factor;
		double framesize_factor;

		/* Take only the desired part of overflow */
		overflow = rc->overflow;

		/* Factor that will take care to decrease the overflow applied
		 * according to the importance of this frame type in term of
		 * overall size */
		frametype_factor  = rc->count[XVID_TYPE_IVOP-1]*rc->avg_length[XVID_TYPE_IVOP-1];
		frametype_factor += rc->count[XVID_TYPE_PVOP-1]*rc->avg_length[XVID_TYPE_PVOP-1];
		frametype_factor += rc->count[XVID_TYPE_BVOP-1]*rc->avg_length[XVID_TYPE_BVOP-1];
		frametype_factor /= rc->count[s->type-1]*rc->avg_length[s->type-1];
		frametype_factor  = 1/frametype_factor;

		/* Factor that will take care not to compensate too much for this frame
		 * size */
		framesize_factor  = dbytes;
		framesize_factor /= rc->avg_length[s->type-1];

		/* Treat only the overflow part concerned by this frame type and size */
		overflow *= frametype_factor;
#if 0
		/* Leave this one alone, as it impacts badly on quality */
		overflow *= framesize_factor;
#endif

		/* Apply the overflow strength imposed by the user */
		overflow *= (rc->param.overflow_control_strength/100.0f);
	} else {
		/* no negative overflow applied in IFrames because:
		 *  - their role is important as they're references for P/BFrames.
		 *  - there aren't much in typical sequences, so if an IFrame overflows too
		 *    much, this overflow may impact the next IFrame too much and generate
		 *    a sequence of poor quality frames */
		overflow = 0;
	}

	/* Make sure we are not trying to compensate more overflow than we even have */
	if (fabs(overflow) > fabs(rc->overflow))
		overflow = rc->overflow;

	/* Make sure the overflow doesn't make the frame size to get out of the range
	 * [-max_degradation..+max_improvment] */
	if (overflow > dbytes*rc->param.max_overflow_improvement / 100) {
		if(overflow <= dbytes)
			dbytes += dbytes * rc->param.max_overflow_improvement / 100;
		else
			dbytes += overflow * rc->param.max_overflow_improvement / 100;
	} else if (overflow < - dbytes * rc->param.max_overflow_degradation / 100) {
		dbytes -= dbytes * rc->param.max_overflow_degradation / 100;
	} else {
		dbytes += overflow;
	}

	/*-------------------------------------------------------------------------
	 * Frame bit allocation last part:
	 *
	 * Cap frame length so we don't reach neither bigger frame sizes than first
	 * pass nor smaller than the allowed minimum.
	 *-----------------------------------------------------------------------*/

#ifdef PASS_SMALLER
	if (dbytes > s->length) {
		dbytes = s->length;
	}
#endif

	/* Prevent stupid desired sizes under logical values */
	if (dbytes < rc->min_length[s->type-1]) {
		dbytes = rc->min_length[s->type-1];
	}

	/*------------------------------------------------------------------------
	 * Desired frame length <-> quantizer mapping
	 *-----------------------------------------------------------------------*/

#ifdef BQUANT_PRESCALE
	/* For bframes we prescale the quantizer to avoid too high quant scaling */
	if(s->type == XVID_TYPE_BVOP) {

		twopass_stat_t *b_ref = s;

		/* Find the reference frame */
		while(b_ref != &rc->stats[0] && b_ref->type == XVID_TYPE_BVOP)
			b_ref--;

		/* Compute the original quant */
		s->quant  = 2*(100*s->quant - data->bquant_offset);
		s->quant += data->bquant_ratio - 1; /* to avoid rounding issues */
		s->quant  = s->quant/data->bquant_ratio - b_ref->quant;
	}
#endif

	/* Don't laugh at this very 'simple' quant<->size relationship, it
	 * proves to be acurate enough for our algorithm */
	scaled_quant = (double)s->quant*(double)s->length/(double)dbytes;

#ifdef COMPENSATE_FORMULA
	/* We know xvidcore will apply the bframe formula again, so we compensate
	 * it right now to make sure we would not apply it twice */
	if(s->type == XVID_TYPE_BVOP) {

		twopass_stat_t *b_ref = s;

		/* Find the reference frame */
		while(b_ref != &rc->stats[0] && b_ref->type == XVID_TYPE_BVOP)
			b_ref--;

		/* Compute the quant it would be if the core did not apply the bframe
		 * formula */
		scaled_quant  = 100*scaled_quant - data->bquant_offset;
		scaled_quant += data->bquant_ratio - 1; /* to avoid rouding issues */
		scaled_quant /= data->bquant_ratio;
	}
#endif

	/* Quantizer has been scaled using floating point operations/results, we
	 * must cast it to integer */
	data->quant = (int)scaled_quant;

	/* Let's clip the computed quantizer, if needed */
	if (data->quant < 1) {
		data->quant = 1;
	} else if (data->quant > 31) {
		data->quant = 31;
	} else {

		/* The frame quantizer has not been clipped, this appears to be a good
		 * computed quantizer, do not loose quantizer decimal part that we
		 * accumulate for later reuse when its sum represents a complete
		 * unit. */
		rc->quant_error[s->type-1][data->quant] += scaled_quant - (double)data->quant;

		if (rc->quant_error[s->type-1][data->quant] >= 1.0) {
			rc->quant_error[s->type-1][data->quant] -= 1.0;
			data->quant++;
		} else if (rc->quant_error[s->type-1][data->quant] <= -1.0) {
			rc->quant_error[s->type-1][data->quant] += 1.0;
			data->quant--;
		}
	}

	/* Now we have a computed quant that is in the right quante range, with a
	 * possible +1 correction due to cumulated error. We can now safely clip
	 * the quantizer again with user's quant ranges. "Safely" means the Rate
	 * Control could learn more about this quantizer, this knowledge is useful
	 * for future frames even if it this quantizer won't be really used atm,
	 * that's why we don't perform this clipping earlier. */
	if (data->quant < data->min_quant[s->type-1]) {
		data->quant = data->min_quant[s->type-1];
	} else if (data->quant > data->max_quant[s->type-1]) {
		data->quant = data->max_quant[s->type-1];
	}

	if (data->quant < rc->min_quant) data->quant = rc->min_quant;

	/* To avoid big quality jumps from frame to frame, we apply a "security"
	 * rule that makes |last_quant - new_quant| <= 2. This rule only applies
	 * to predicted frames (P and B) */
	if (s->type != XVID_TYPE_IVOP && rc->last_quant[s->type-1] && capped_to_max_framesize == 0) {

		if (data->quant > rc->last_quant[s->type-1] + 2) {
			data->quant = rc->last_quant[s->type-1] + 2;
			DPRINTF(XVID_DEBUG_RC,
					"[xvid rc] -- frame %d p/b-frame quantizer prevented from rising too steeply\n",
					data->frame_num);
		}
		if (data->quant < rc->last_quant[s->type-1] - 2) {
			data->quant = rc->last_quant[s->type-1] - 2;
			DPRINTF(XVID_DEBUG_RC,
					"[xvid rc] -- frame:%d p/b-frame quantizer prevented from falling too steeply\n",
					data->frame_num);
		}
	}

	/* We don't want to pollute the RC histerisis when our computed quant has
	 * been computed from a capped frame size */
	if (capped_to_max_framesize == 0)
		rc->last_quant[s->type-1] = data->quant;

	/* Don't forget to force 1st pass frame type ;-) */
	data->type = s->type;

	return 0;
}

/*----------------------------------------------------------------------------
 *--------------------------------------------------------------------------*/

static int
rc_2pass2_after(rc_2pass2_t * rc, xvid_plg_data_t * data)
{
	const char frame_type[4] = { 'i', 'p', 'b', 's'};
	twopass_stat_t * s = &rc->stats[data->frame_num];

	/* Insufficent stats data */
	if (data->frame_num >= rc->num_frames)
		return 0;

	/* Update the quantizer counter */
	rc->quant_count[s->type-1][data->quant]++;

	/* Update the frame type overflow */
	if (data->type == XVID_TYPE_IVOP) {
		int kfdiff = 0;

		if(rc->KF_idx != rc->num_frames -1) {
			kfdiff  = rc->keyframe_locations[rc->KF_idx+1];
			kfdiff -= rc->keyframe_locations[rc->KF_idx];
		}

		/* Flush Keyframe overflow accumulator */
		rc->overflow += rc->KFoverflow;

		/* Store the frame overflow to the keyframe accumulator */
		rc->KFoverflow = s->desired_length - data->length;

		if (kfdiff > 1) {
			/* Non-consecutive keyframes case:
			 * We can then divide this total keyframe overflow into equal parts
			 * that we will distribute into regular overflow at each frame
			 * between the sequence bounded by two IFrames */
			rc->KFoverflow_partial = rc->KFoverflow / (kfdiff - 1);
		} else {
			/* Consecutive keyframes case:
			 * Flush immediatly the keyframe overflow and reset keyframe
			 * overflow */
			rc->overflow += rc->KFoverflow;
			rc->KFoverflow = 0;
			rc->KFoverflow_partial = 0;
		}
		rc->KF_idx++;
	} else {
		/* Accumulate the frame overflow */
		rc->overflow += s->desired_length - data->length;

		/* Distribute part of the keyframe overflow */
		rc->overflow += rc->KFoverflow_partial;

		/* Don't forget to substract that same amount from the total keyframe
		 * overflow */
		rc->KFoverflow -= rc->KFoverflow_partial;
	}

	s->error = s->desired_length - data->length;
	rc->real_total += data->length;

	DPRINTF(XVID_DEBUG_RC, "[xvid rc] -- frame:%d type:%c quant:%d stats:%d scaled:%d desired:%d actual:%d error:%d overflow:%.2f\n",
			data->frame_num,
			frame_type[data->type-1],
			data->quant,
			s->length,
			s->scaled_length,
			s->desired_length,
			s->desired_length - s->error,
			-s->error,
			rc->overflow);

	return(0);
}

/*****************************************************************************
 * Helper functions definition
 ****************************************************************************/

/* Default buffer size for reading lines */
#define BUF_SZ   1024

/* Helper functions for reading/parsing the stats file */
static char *skipspaces(char *string);
static int iscomment(char *string);
static char *readline(FILE *f);

/* This function counts the number of frame entries in the stats file
 * It also counts the number of I Frames */
static int
statsfile_count_frames(rc_2pass2_t * rc, char * filename)
{
	FILE * f;
	char *line;
	int lines;

	rc->num_frames = 0;
	rc->num_keyframes = 0;

	if ((f = fopen(filename, "rb")) == NULL)
		return(-1);

	lines = 0;
	while ((line = readline(f)) != NULL) {

		char *ptr;
		char type;
		int fields;

		lines++;

		/* We skip spaces */
		ptr = skipspaces(line);

		/* Skip coment lines or empty lines */
		if(iscomment(ptr) || *ptr == '\0') {
			free(line);
			continue;
		}

		/* Read the stat line from buffer */
		fields = sscanf(ptr, "%c", &type);

		/* Valid stats files have at least 7 fields */
		if (fields == 1) {
			switch(type) {
			case 'i':
			case 'I':
				rc->num_keyframes++;