近期参与了Android程序开发,涉及到音视频。由于Android的窗口模式不同于传统的窗口,有时候需要对图像进行90度旋转。对图像旋转主要是对YUV图片的旋转,以下代码是将一个格式为YUV420的图片进行逆时针旋转。
void yuv_rotate_90(uchar *des,uchar *src,int width,int height)
{
int n = 0;
int hw = width>>1;
int hh = height>>1;
int size = width * height;
int hsize = size>>2;
int pos = 0;
//copy y
for(int j = 0; j < width;j++)
{
pos = size;
for(int i = height - 1; i >= 0; i--)
{ pos-=width;
des[n++] = src[pos + j];
}
}
//copy uv
uchar *ptemp = src + size;
int m = n + hsize;
for(int j = 0;j < hw;j++)
{ pos= hsize;
for(int i = hh - 1;i >= 0;i--)
{
pos-=hw;
des[n++] = ptemp[ pos + j ];
des[m++] = ptemp[ pos + j+ hsize ];
}
}
}
很多音视频相关的项目里面用到了ffmpeg,对ffmpeg里面的视频帧进行旋转主要是在视频解码后,图片显示前完成,于是将以上代码改到ffmpeg的应用环境。ffmpeg里面解码完成后的视频帧结构是AVFrame,以下代码是所述代码。
逆时针90度
void frame_rotate_90( AVFrame *src,AVFrame*des)
{
int n = 0;
int hw = src->width>>1;
int hh = src->height>>1;
int size = src->width * src->height;
int hsize = size>>2;
int pos = 0;
//copy y
for(int j = 0; j < src->width;j++)
{
pos = size;
for(int i = src->height - 1; i >= 0; i--)
{ pos-=src->width;
des->data[0][n++] = src->data[0][pos + j];
}
}
//copy uv
n = 0;
for(int j = 0;j < hw;j++)
{ pos= hsize;
for(int i = hh - 1;i >= 0;i--)
{
pos-=hw;
des->data[1][n] = src->data[1][ pos + j];
des->data[2][n] = src->data[2][ pos + j];
n++;
}
}
des->linesize[0] = src->height;
des->linesize[1] = src->height>>1;
des->linesize[2] = src->height>>1;
des->height = src->width;
des->width = src->height;
}
逆时针180度旋转
void frame_rotate_180(AVFrame *src,AVFrame*des)
{
int n = 0,i= 0,j = 0;
int hw = src->width>>1;
int hh = src->height>>1;
int pos= src->width * src->height;
for (i = 0; i < src->height; i++)
{
pos-= src->width;
for (int j = 0; j < src->width; j++) {
des->data[0][n++] = src->data[0][pos + j];
}
}
n = 0;
pos = src->width * src->height>>2;
for (i = 0; i < hh;i++) {
pos-= hw;
for (int j = 0; j < hw;j++) {
des->data[1][n] = src->data[1][ pos + j];
des->data[2][n] = src->data[2][ pos + j];
n++;
}
}
des->linesize[0] = src->width;
des->linesize[1] = src->width>>1;
des->linesize[2] = src->width>>1;
des->width = src->width;
des->height = src->height;
des->format = src->format;
des->pts = src->pts;
des->pkt_pts = src->pkt_pts;
des->pkt_dts = src->pkt_dts;
des->key_frame = src->key_frame;
}
逆时针270度旋转:
void frame_rotate_270(AVFrame *src,AVFrame*des)
{
int n = 0,i= 0,j = 0;
int hw = src->width>>1;
int hh = src->height>>1;
int pos = 0;
for(i = src->width-1;i >= 0;i--)
{
pos = 0;
for(j= 0;j < src->height;j++)
{
des->data[0][n++]= src->data[0][pos+i];
pos += src->width;
}
}
n = 0;
for (i = hw-1; i >= 0;i--) {
pos= 0;
for (j = 0; j < hh;j++) {
des->data[1][n]= src->data[1][pos+i];
des->data[2][n]= src->data[2][pos+i];
pos += hw;
n++;
}
}
des->linesize[0] = src->height;
des->linesize[1] = src->height>>1;
des->linesize[2] = src->height>>1;
des->width = src->height;
des->height = src->width;
des->format = src->format;
des->pts = src->pts;
des->pkt_pts = src->pkt_pts;
des->pkt_dts = src->pkt_dts;
des->key_frame = src->key_frame;
}
注意:
1,在ffmpeg环境下,调用frame_rotate系列函数之前需要对 AVFrame*des 进行初始化,否则内存是否发进行拷贝的。初始化代码如下:AVFrame *des = av_frame_alloc();
unsigned char *rotate_buffer=(unsigned char *)av_malloc(av_image_get_buffer_size(AV_PIX_FMT_YUV420P, pCodecCtx->height, pCodecCtx->width,1));
av_image_fill_arrays(des->data, des->linesize,rotate_buffer,AV_PIX_FMT_YUV420P,pCodecCtx->height, pCodecCtx->width,1);
2,经过旋转后,视频帧的宽和高已经发生了变化,所以进行显示时,应该以旋转后的宽高进行显示,不再是AVCodecContext里面的宽和高,SDL里面的Window和Texture都要进行调整,否则图片会花,或者崩溃。
参考:
1,http://blog.csdn.net/kl222/article/details/24470305 感觉算法有点问题,图片经过旋转后UV部分存在问题。
2,http://blog.csdn.net/codefoxtiger/article/details/23549553 算法对,但是性能需要优化,旋转一次,会调用太多乘法,对Android环境不太适用。