dvd 字幕缩放测试代码 (thinkvd开发日志)

这个测试代码字幕放大时效果还可以，但缩小时无论怎么调整有关参数：
1. sws_getContext中的flags相关，
2。sws_getGaussianVec(0.25, 3.0);
都比较难让人满意，当画面缩小时，与主流的dvd converter 转换器还有点差异.

void subtitle_scale(AVCodecContext *c)
{
struct SwsContext *pSWSCtx;
AVFrame *pFrameRGB;
int i, format, numBytes;
uint8_t *buffer;
AVPicture *picture;
static SwsFilter filter;
static int firsttime = 1;

for (int i = 0; i < subtitle_av.num_rects; i++){
int width = subtitle_av.rects[i]->w;
int height= subtitle_av.rects[i]->h;

c->width = (int)(width * subtitle_info.ratio_w);
c->height= (int)(height* subtitle_info.ratio_h);
if(c->width%4!=0)
c->width=c->width+4-c->width%4;

pFrameRGB = avcodec_alloc_frame();
if (pFrameRGB==NULL){
printf("avcodec alloc frame failed!/n");
continue;
}

if (firsttime) {
filter.lumH = filter.lumV =
filter.chrH = filter.chrV = sws_getGaussianVec(0.25, 3.0);
sws_normalizeVec(filter.lumH, 1.0);
firsttime = 0;
}

format = PIX_FMT_GRAY8;
numBytes=avpicture_get_size(format, c->width, c->height);
buffer= av_malloc(numBytes);
avpicture_fill((AVPicture *)pFrameRGB, buffer, format, c->width, c->height);

pSWSCtx = sws_getContext(
width, height,
format,
c->width, c->height,
format, SWS_BICUBIC, &filter, NULL, NULL);
//dumpInfo("w=%d, pitch=%d", c->width, c->width);

sws_scale(pSWSCtx, subtitle_av.rects[i]->pict.data, subtitle_av.rects[i]->pict.linesize,
0, height, pFrameRGB->data, pFrameRGB->linesize);

subtitle_av.rects[i]->w = c->width;
subtitle_av.rects[i]->h = c->height;
subtitle_av.rects[i]->x = (subtitle_info.video_out_w - c->width)>>1;
av_free(subtitle_av.rects[i]->pict.data[0]);
subtitle_av.rects[i]->pict.data[0] = av_malloc(c->width * c->height);
memcpy(subtitle_av.rects[i]->pict.data[0], pFrameRGB->data[0], c->width * c->height);
subtitle_av.rects[i]->pict.linesize[0] = pFrameRGB->linesize[0];

av_free(buffer);
av_free(pFrameRGB);
sws_freeContext(pSWSCtx);
}
}