ratecontrol.c

基于Linux的ffmepg decoder

#include <math.h>
#include "ratecontrol.h"

/*****************************************************************************
 * Local prototype - defined at the end of the file
 ****************************************************************************/

static int get_initial_quant(uint32_t bpp);

/*****************************************************************************
 * RateControlInit
 *
 * This function initialize the structure members of 'rate_control' argument
 * according to the other arguments.
 *
 * Returned value : None
 *
 ****************************************************************************/

void
RateControlInit(RateControl * rate_control,
				uint32_t target_rate,
				uint32_t reaction_delay_factor,
				uint32_t averaging_period,
				uint32_t buffer,
				int framerate,
				int max_quant,
				int min_quant)
{
	int i;
	rate_control->frames = 0;
	rate_control->total_size = 0;
	rate_control->framerate = (double) framerate / 1000.0;
	rate_control->target_rate = (int32_t) target_rate;
	rate_control->rtn_quant = get_initial_quant(target_rate);
	rate_control->max_quant = (int16_t) max_quant;
	rate_control->min_quant = (int16_t) min_quant;
	for (i = 0; i < 32; ++i) {
		rate_control->quant_error[i] = 0.0;
	}
	rate_control->target_framesize =
		(double) target_rate / 8.0 / rate_control->framerate;
	rate_control->sequence_quality = 2.0 / (double) rate_control->rtn_quant;
	rate_control->avg_framesize = rate_control->target_framesize;
	rate_control->reaction_delay_factor = (int32_t) reaction_delay_factor;
	rate_control->averaging_period = (int32_t) averaging_period;
	rate_control->buffer = (int32_t) buffer;
}

/*****************************************************************************
 * RateControlGetQ
 *
 * Returned value : - the current 'rate_control' quantizer value
 *
 ****************************************************************************/

/*****************************************************************************
 * RateControlUpdate
 *
 * This function is called once a coded frame to update all internal
 * parameters of 'rate_control'.
 *
 * Returned value : None
 *
 ****************************************************************************/

void
RateControlUpdate(RateControl *rate_control,
				  int16_t quant,
				  int frame_size,
				  int keyframe)
{
	int64_t deviation;
	double overflow, averaging_period, reaction_delay_factor;
	double quality_scale, base_quality, target_quality;
	int32_t rtn_quant;

	rate_control->frames++;
	rate_control->total_size += frame_size;

	deviation =
		(int64_t) ((double) rate_control->total_size -
				   ((double) ((double) rate_control->target_rate / 8.0 /
					 (double) rate_control->framerate) * (double) rate_control->frames));

	if (rate_control->rtn_quant >= 2) {
		averaging_period = (double) rate_control->averaging_period;
		rate_control->sequence_quality -=
			rate_control->sequence_quality / averaging_period;
		rate_control->sequence_quality +=
			2.0 / (double) rate_control->rtn_quant / averaging_period;
		if (rate_control->sequence_quality < 0.1)
			rate_control->sequence_quality = 0.1;

		if (!keyframe) {
			reaction_delay_factor =
				(double) rate_control->reaction_delay_factor;
			rate_control->avg_framesize -=
				rate_control->avg_framesize / reaction_delay_factor;
			rate_control->avg_framesize += frame_size / reaction_delay_factor;
		}
	}

	quality_scale =
		rate_control->target_framesize / rate_control->avg_framesize *
		rate_control->target_framesize / rate_control->avg_framesize;

	base_quality = rate_control->sequence_quality;
	if (quality_scale >= 1.0) {
		base_quality = 1.0 - (1.0 - base_quality) / quality_scale;
	} else {
		base_quality = 0.06452 + (base_quality - 0.06452) * quality_scale;
	}

	overflow = -((double) deviation / (double) rate_control->buffer);

	target_quality =
		base_quality + (base_quality -
						0.06452) * overflow / rate_control->target_framesize;

	if (target_quality > 2.0)
		target_quality = 2.0;
	else if (target_quality < 0.06452)
		target_quality = 0.06452;

	rtn_quant = (int32_t) (2.0 / target_quality);

	if (rtn_quant < 31) {
		rate_control->quant_error[rtn_quant] +=
			2.0 / target_quality - rtn_quant;
		if (rate_control->quant_error[rtn_quant] >= 1.0) {
			rate_control->quant_error[rtn_quant] -= 1.0;
			rtn_quant++;
		}
	}

	if (rtn_quant > rate_control->rtn_quant + 1)
		rtn_quant = rate_control->rtn_quant + 1;
	else if (rtn_quant < rate_control->rtn_quant - 1)
		rtn_quant = rate_control->rtn_quant - 1;

	if (rtn_quant > rate_control->max_quant)
		rtn_quant = rate_control->max_quant;
	else if (rtn_quant < rate_control->min_quant)
		rtn_quant = rate_control->min_quant;
	rate_control->rtn_quant = rtn_quant;
}

/*****************************************************************************
 * Local functions
 ****************************************************************************/

static int
get_initial_quant(uint32_t bpp)
{
	return 4;
}