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FFmpeg源代码简单分析#xff1a;libswscale的sws_scale()_雷霄骅的博客-CSDN博客_bad dst image pointers
libswscale的sws_scale()
FFmpeg的图像处理#xff08;缩放#xff0c;YUV/RGB格式转换#xff09;类库libswsscale中的sws_scale()函数。libswscale是一…参考链接
FFmpeg源代码简单分析libswscale的sws_scale()_雷霄骅的博客-CSDN博客_bad dst image pointers
libswscale的sws_scale()
FFmpeg的图像处理缩放YUV/RGB格式转换类库libswsscale中的sws_scale()函数。libswscale是一个主要用于处理图片像素数据的类库。可以完成图片像素格式的转换图片的拉伸等工作。该类库常用的函数数量很少一般情况下就3个 sws_getContext()初始化一个SwsContext。sws_scale()处理图像数据。sws_freeContext()释放一个SwsContext。
Libswscale处理数据流程
Libswscale处理像素数据的流程可以概括为下图从图中可以看出libswscale处理数据有两条最主要的方式unscaled和scaled。unscaled用于处理不需要拉伸的像素数据属于比较特殊的情况scaled用于处理需要拉伸的像素数据。Unscaled只需要对图像像素格式进行转换而Scaled则除了对像素格式进行转换之外还需要对图像进行缩放。Scaled方式可以分成以下几个步骤 XXX to YUV Converter首先将数据像素数据转换为8bitYUV格式Horizontal scaler水平拉伸图像并且转换为15bitYUVVertical scaler垂直拉伸图像Output converter转换为输出像素格式。
sws_scale()
sws_scale()是用于转换像素的函数。它的声明位于libswscale\swscale.h如下所示。
/*** Scale the image slice in srcSlice and put the resulting scaled* slice in the image in dst. A slice is a sequence of consecutive* rows in an image.** Slices have to be provided in sequential order, either in* top-bottom or bottom-top order. If slices are provided in* non-sequential order the behavior of the function is undefined.** param c the scaling context previously created with* sws_getContext()* param srcSlice the array containing the pointers to the planes of* the source slice* param srcStride the array containing the strides for each plane of* the source image* param srcSliceY the position in the source image of the slice to* process, that is the number (counted starting from* zero) in the image of the first row of the slice* param srcSliceH the height of the source slice, that is the number* of rows in the slice* param dst the array containing the pointers to the planes of* the destination image* param dstStride the array containing the strides for each plane of* the destination image* return the height of the output slice*/
int sws_scale(struct SwsContext *c, const uint8_t *const srcSlice[],const int srcStride[], int srcSliceY, int srcSliceH,uint8_t *const dst[], const int dstStride[]);
sws_scale()的定义位于libswscale\swscale.c如下所示。
/*** swscale wrapper, so we dont need to export the SwsContext.* Assumes planar YUV to be in YUV order instead of YVU.*/
int attribute_align_arg sws_scale(struct SwsContext *c,const uint8_t * const srcSlice[],const int srcStride[], int srcSliceY,int srcSliceH, uint8_t *const dst[],const int dstStride[])
{if (c-nb_slice_ctx)c c-slice_ctx[0];return scale_internal(c, srcSlice, srcStride, srcSliceY, srcSliceH,dst, dstStride, 0, c-dstH);
}sws_scale内部调用了scale_internalscale_internal函数封装了sws_scale的大多数代码
static int scale_internal(SwsContext *c,const uint8_t * const srcSlice[], const int srcStride[],int srcSliceY, int srcSliceH,uint8_t *const dstSlice[], const int dstStride[],int dstSliceY, int dstSliceH)
{const int scale_dst dstSliceY 0 || dstSliceH c-dstH;const int frame_start scale_dst || !c-sliceDir;int i, ret;const uint8_t *src2[4];uint8_t *dst2[4];int macro_height_src isBayer(c-srcFormat) ? 2 : (1 c-chrSrcVSubSample);int macro_height_dst isBayer(c-dstFormat) ? 2 : (1 c-chrDstVSubSample);// copy strides, so they can safely be modifiedint srcStride2[4];int dstStride2[4];int srcSliceY_internal srcSliceY;if (!srcStride || !dstStride || !dstSlice || !srcSlice) {av_log(c, AV_LOG_ERROR, One of the input parameters to sws_scale() is NULL, please check the calling code\n);return AVERROR(EINVAL);}if ((srcSliceY (macro_height_src - 1)) ||((srcSliceH (macro_height_src - 1)) srcSliceY srcSliceH ! c-srcH) ||srcSliceY srcSliceH c-srcH) {av_log(c, AV_LOG_ERROR, Slice parameters %d, %d are invalid\n, srcSliceY, srcSliceH);return AVERROR(EINVAL);}if ((dstSliceY (macro_height_dst - 1)) ||((dstSliceH (macro_height_dst - 1)) dstSliceY dstSliceH ! c-dstH) ||dstSliceY dstSliceH c-dstH) {av_log(c, AV_LOG_ERROR, Slice parameters %d, %d are invalid\n, dstSliceY, dstSliceH);return AVERROR(EINVAL);}if (!check_image_pointers(srcSlice, c-srcFormat, srcStride)) {av_log(c, AV_LOG_ERROR, bad src image pointers\n);return AVERROR(EINVAL);}if (!check_image_pointers((const uint8_t* const*)dstSlice, c-dstFormat, dstStride)) {av_log(c, AV_LOG_ERROR, bad dst image pointers\n);return AVERROR(EINVAL);}// do not mess up sliceDir if we have a trailing 0-size sliceif (srcSliceH 0)return 0;if (c-gamma_flag c-cascaded_context[0])return scale_gamma(c, srcSlice, srcStride, srcSliceY, srcSliceH,dstSlice, dstStride, dstSliceY, dstSliceH);if (c-cascaded_context[0] srcSliceY 0 srcSliceH c-cascaded_context[0]-srcH)return scale_cascaded(c, srcSlice, srcStride, srcSliceY, srcSliceH,dstSlice, dstStride, dstSliceY, dstSliceH);if (!srcSliceY (c-flags SWS_BITEXACT) c-dither SWS_DITHER_ED c-dither_error[0])for (i 0; i 4; i)memset(c-dither_error[i], 0, sizeof(c-dither_error[0][0]) * (c-dstW2));if (usePal(c-srcFormat))update_palette(c, (const uint32_t *)srcSlice[1]);memcpy(src2, srcSlice, sizeof(src2));memcpy(dst2, dstSlice, sizeof(dst2));memcpy(srcStride2, srcStride, sizeof(srcStride2));memcpy(dstStride2, dstStride, sizeof(dstStride2));if (frame_start !scale_dst) {if (srcSliceY ! 0 srcSliceY srcSliceH ! c-srcH) {av_log(c, AV_LOG_ERROR, Slices start in the middle!\n);return AVERROR(EINVAL);}c-sliceDir (srcSliceY 0) ? 1 : -1;} else if (scale_dst)c-sliceDir 1;if (c-src0Alpha !c-dst0Alpha isALPHA(c-dstFormat)) {uint8_t *base;int x,y;av_fast_malloc(c-rgb0_scratch, c-rgb0_scratch_allocated,FFABS(srcStride[0]) * srcSliceH 32);if (!c-rgb0_scratch)return AVERROR(ENOMEM);base srcStride[0] 0 ? c-rgb0_scratch - srcStride[0] * (srcSliceH-1) :c-rgb0_scratch;for (y0; ysrcSliceH; y){memcpy(base srcStride[0]*y, src2[0] srcStride[0]*y, 4*c-srcW);for (xc-src0Alpha-1; x4*c-srcW; x4) {base[ srcStride[0]*y x] 0xFF;}}src2[0] base;}if (c-srcXYZ !(c-dstXYZ c-srcWc-dstW c-srcHc-dstH)) {uint8_t *base;av_fast_malloc(c-xyz_scratch, c-xyz_scratch_allocated,FFABS(srcStride[0]) * srcSliceH 32);if (!c-xyz_scratch)return AVERROR(ENOMEM);base srcStride[0] 0 ? c-xyz_scratch - srcStride[0] * (srcSliceH-1) :c-xyz_scratch;xyz12Torgb48(c, (uint16_t*)base, (const uint16_t*)src2[0], srcStride[0]/2, srcSliceH);src2[0] base;}if (c-sliceDir ! 1) {// slices go from bottom to top we flip the image internallyfor (i0; i4; i) {srcStride2[i] * -1;dstStride2[i] * -1;}src2[0] (srcSliceH - 1) * srcStride[0];if (!usePal(c-srcFormat))src2[1] ((srcSliceH c-chrSrcVSubSample) - 1) * srcStride[1];src2[2] ((srcSliceH c-chrSrcVSubSample) - 1) * srcStride[2];src2[3] (srcSliceH - 1) * srcStride[3];dst2[0] ( c-dstH - 1) * dstStride[0];dst2[1] ((c-dstH c-chrDstVSubSample) - 1) * dstStride[1];dst2[2] ((c-dstH c-chrDstVSubSample) - 1) * dstStride[2];dst2[3] ( c-dstH - 1) * dstStride[3];srcSliceY_internal c-srcH-srcSliceY-srcSliceH;}reset_ptr(src2, c-srcFormat);reset_ptr((void*)dst2, c-dstFormat);if (c-convert_unscaled) {int offset srcSliceY_internal;int slice_h srcSliceH;// for dst slice scaling, offset the pointers to match the unscaled APIif (scale_dst) {av_assert0(offset 0);for (i 0; i 4 src2[i]; i) {if (!src2[i] || (i 0 usePal(c-srcFormat)))break;src2[i] (dstSliceY ((i 1 || i 2) ? c-chrSrcVSubSample : 0)) * srcStride2[i];}for (i 0; i 4 dst2[i]; i) {if (!dst2[i] || (i 0 usePal(c-dstFormat)))break;dst2[i] - (dstSliceY ((i 1 || i 2) ? c-chrDstVSubSample : 0)) * dstStride2[i];}offset dstSliceY;slice_h dstSliceH;}ret c-convert_unscaled(c, src2, srcStride2, offset, slice_h,dst2, dstStride2);if (scale_dst)dst2[0] dstSliceY * dstStride2[0];} else {ret swscale(c, src2, srcStride2, srcSliceY_internal, srcSliceH,dst2, dstStride2, dstSliceY, dstSliceH);}if (c-dstXYZ !(c-srcXYZ c-srcWc-dstW c-srcHc-dstH)) {uint16_t *dst16;if (scale_dst) {dst16 (uint16_t *)dst2[0];} else {int dstY c-dstY ? c-dstY : srcSliceY srcSliceH;av_assert0(dstY ret);av_assert0(ret 0);av_assert0(c-dstH dstY);dst16 (uint16_t*)(dst2[0] (dstY - ret) * dstStride2[0]);}/* replace on the same data */rgb48Toxyz12(c, dst16, dst16, dstStride2[0]/2, ret);}/* reset slice direction at end of frame */if ((srcSliceY_internal srcSliceH c-srcH) || scale_dst)c-sliceDir 0;return ret;
}从sws_scale()的定义可以看出它封装了SwsContext中的swscale()注意这个函数中间没有“_”。函数最重要的一句代码就是“swscale()”。除此之外函数还做了一些增加“兼容性”的一些处理。函数的主要步骤如下所示。
1.检查输入的图像参数的合理性。
这一步骤首先检查输入输出的参数是否为空然后通过调用check_image_pointers()检查输入输出图像的内存是否正确分配。check_image_pointers()的定义如下所示。
static int check_image_pointers(const uint8_t * const data[4], enum AVPixelFormat pix_fmt,const int linesizes[4])
{const AVPixFmtDescriptor *desc av_pix_fmt_desc_get(pix_fmt);int i;av_assert2(desc);for (i 0; i 4; i) {int plane desc-comp[i].plane;if (!data[plane] || !linesizes[plane])return 0;}return 1;
}从check_image_pointers()的定义可以看出在特定像素格式前提下如果该像素格式应该包含像素的分量为空就返回0否则返回1。
2.如果输入像素数据中使用了“调色板”palette则进行一些相应的处理。
这一步通过函数usePal()来判定。usePal()的定义如下。
static av_always_inline int usePal(enum AVPixelFormat pix_fmt)
{switch (pix_fmt) {case AV_PIX_FMT_PAL8:case AV_PIX_FMT_BGR4_BYTE:case AV_PIX_FMT_BGR8:case AV_PIX_FMT_GRAY8:case AV_PIX_FMT_RGB4_BYTE:case AV_PIX_FMT_RGB8:return 1;default:return 0;}
}
3.其它一些特殊格式的处理比如说AlphaXYZ等的处理这方面没有研究过。 4.如果输入的图像的扫描方式是从底部到顶部的一般情况下是从顶部到底部则将图像进行反转。 5.调用SwsContext中的swscale()。 SwsContext中的swscale()
swscale这个变量的类型是SwsFunc实际上就是一个函数指针。它是整个类库的核心。当我们从外部调用swscale()函数的时候实际上就是调用了SwsContext中的这个名称为swscale的变量注意外部函数接口和这个内部函数指针的名字是一样的但不是一回事。可以看一下SwsFunc这个类型的定义
typedef int (*SwsFunc)(struct SwsContext *context, const uint8_t *src[],int srcStride[], int srcSliceY, int srcSliceH,uint8_t *dst[], int dstStride[]);可以看出SwsFunc的定义的参数类型和libswscale类库外部接口函数swscale()的参数类型一模一样。在libswscale中该指针的指向可以分成2种情况 1.图像没有伸缩的时候指向专有的像素转换函数2.图像有伸缩的时候指向swscale()函数。在调用sws_getContext()初始化SwsContext的时候会在其子函数sws_init_context()中对swscale指针进行赋值。如果图像没有进行拉伸则会调用ff_get_unscaled_swscale()对其进行赋值如果图像进行了拉伸则会调用ff_getSwsFunc()对其进行赋值。下面分别看一下这2种情况。
没有拉伸--专有的像素转换函数
如果图像没有进行拉伸则会调用ff_get_unscaled_swscale()对SwsContext的swscale进行赋值。上篇文章中记录了这个函数在这里回顾一下。
ff_get_unscaled_swscale()
ff_get_unscaled_swscale()的定义如下。
void ff_get_unscaled_swscale(SwsContext *c)
{const enum AVPixelFormat srcFormat c-srcFormat;const enum AVPixelFormat dstFormat c-dstFormat;const int flags c-flags;const int dstH c-dstH;const int dstW c-dstW;int needsDither;needsDither isAnyRGB(dstFormat) c-dstFormatBpp 24 (c-dstFormatBpp c-srcFormatBpp || (!isAnyRGB(srcFormat)));/* yv12_to_nv12 */if ((srcFormat AV_PIX_FMT_YUV420P || srcFormat AV_PIX_FMT_YUVA420P) (dstFormat AV_PIX_FMT_NV12 || dstFormat AV_PIX_FMT_NV21)) {c-convert_unscaled planarToNv12Wrapper;}/* yv24_to_nv24 */if ((srcFormat AV_PIX_FMT_YUV444P || srcFormat AV_PIX_FMT_YUVA444P) (dstFormat AV_PIX_FMT_NV24 || dstFormat AV_PIX_FMT_NV42)) {c-convert_unscaled planarToNv24Wrapper;}/* nv12_to_yv12 */if (dstFormat AV_PIX_FMT_YUV420P (srcFormat AV_PIX_FMT_NV12 || srcFormat AV_PIX_FMT_NV21)) {c-convert_unscaled nv12ToPlanarWrapper;}/* nv24_to_yv24 */if (dstFormat AV_PIX_FMT_YUV444P (srcFormat AV_PIX_FMT_NV24 || srcFormat AV_PIX_FMT_NV42)) {c-convert_unscaled nv24ToPlanarWrapper;}/* yuv2bgr */if ((srcFormat AV_PIX_FMT_YUV420P || srcFormat AV_PIX_FMT_YUV422P ||srcFormat AV_PIX_FMT_YUVA420P) isAnyRGB(dstFormat) !(flags SWS_ACCURATE_RND) (c-dither SWS_DITHER_BAYER || c-dither SWS_DITHER_AUTO) !(dstH 1)) {c-convert_unscaled ff_yuv2rgb_get_func_ptr(c);c-dst_slice_align 2;}/* yuv420p1x_to_p01x */if ((srcFormat AV_PIX_FMT_YUV420P10 || srcFormat AV_PIX_FMT_YUVA420P10 ||srcFormat AV_PIX_FMT_YUV420P12 ||srcFormat AV_PIX_FMT_YUV420P14 ||srcFormat AV_PIX_FMT_YUV420P16 || srcFormat AV_PIX_FMT_YUVA420P16) (dstFormat AV_PIX_FMT_P010 || dstFormat AV_PIX_FMT_P016)) {c-convert_unscaled planarToP01xWrapper;}/* yuv420p_to_p01xle */if ((srcFormat AV_PIX_FMT_YUV420P || srcFormat AV_PIX_FMT_YUVA420P) (dstFormat AV_PIX_FMT_P010LE || dstFormat AV_PIX_FMT_P016LE)) {c-convert_unscaled planar8ToP01xleWrapper;}if (srcFormat AV_PIX_FMT_YUV410P !(dstH 3) (dstFormat AV_PIX_FMT_YUV420P || dstFormat AV_PIX_FMT_YUVA420P) !(flags SWS_BITEXACT)) {c-convert_unscaled yvu9ToYv12Wrapper;c-dst_slice_align 4;}/* bgr24toYV12 */if (srcFormat AV_PIX_FMT_BGR24 (dstFormat AV_PIX_FMT_YUV420P || dstFormat AV_PIX_FMT_YUVA420P) !(flags SWS_ACCURATE_RND) !(dstW1))c-convert_unscaled bgr24ToYv12Wrapper;/* RGB/BGR - RGB/BGR (no dither needed forms) */if (isAnyRGB(srcFormat) isAnyRGB(dstFormat) findRgbConvFn(c) (!needsDither || (c-flags(SWS_FAST_BILINEAR|SWS_POINT))))c-convert_unscaled rgbToRgbWrapper;/* RGB to planar RGB */if ((srcFormat AV_PIX_FMT_GBRP dstFormat AV_PIX_FMT_GBRAP) ||(srcFormat AV_PIX_FMT_GBRAP dstFormat AV_PIX_FMT_GBRP))c-convert_unscaled planarRgbToplanarRgbWrapper;#define isByteRGB(f) ( \f AV_PIX_FMT_RGB32 || \f AV_PIX_FMT_RGB32_1 || \f AV_PIX_FMT_RGB24 || \f AV_PIX_FMT_BGR32 || \f AV_PIX_FMT_BGR32_1 || \f AV_PIX_FMT_BGR24)if (srcFormat AV_PIX_FMT_GBRP isPlanar(srcFormat) isByteRGB(dstFormat))c-convert_unscaled planarRgbToRgbWrapper;if (srcFormat AV_PIX_FMT_GBRAP isByteRGB(dstFormat))c-convert_unscaled planarRgbaToRgbWrapper;if ((srcFormat AV_PIX_FMT_RGB48LE || srcFormat AV_PIX_FMT_RGB48BE ||srcFormat AV_PIX_FMT_BGR48LE || srcFormat AV_PIX_FMT_BGR48BE ||srcFormat AV_PIX_FMT_RGBA64LE || srcFormat AV_PIX_FMT_RGBA64BE ||srcFormat AV_PIX_FMT_BGRA64LE || srcFormat AV_PIX_FMT_BGRA64BE) (dstFormat AV_PIX_FMT_GBRP9LE || dstFormat AV_PIX_FMT_GBRP9BE ||dstFormat AV_PIX_FMT_GBRP10LE || dstFormat AV_PIX_FMT_GBRP10BE ||dstFormat AV_PIX_FMT_GBRP12LE || dstFormat AV_PIX_FMT_GBRP12BE ||dstFormat AV_PIX_FMT_GBRP14LE || dstFormat AV_PIX_FMT_GBRP14BE ||dstFormat AV_PIX_FMT_GBRP16LE || dstFormat AV_PIX_FMT_GBRP16BE ||dstFormat AV_PIX_FMT_GBRAP10LE || dstFormat AV_PIX_FMT_GBRAP10BE ||dstFormat AV_PIX_FMT_GBRAP12LE || dstFormat AV_PIX_FMT_GBRAP12BE ||dstFormat AV_PIX_FMT_GBRAP16LE || dstFormat AV_PIX_FMT_GBRAP16BE ))c-convert_unscaled Rgb16ToPlanarRgb16Wrapper;if ((srcFormat AV_PIX_FMT_GBRP9LE || srcFormat AV_PIX_FMT_GBRP9BE ||srcFormat AV_PIX_FMT_GBRP16LE || srcFormat AV_PIX_FMT_GBRP16BE ||srcFormat AV_PIX_FMT_GBRP10LE || srcFormat AV_PIX_FMT_GBRP10BE ||srcFormat AV_PIX_FMT_GBRP12LE || srcFormat AV_PIX_FMT_GBRP12BE ||srcFormat AV_PIX_FMT_GBRP14LE || srcFormat AV_PIX_FMT_GBRP14BE ||srcFormat AV_PIX_FMT_GBRAP10LE || srcFormat AV_PIX_FMT_GBRAP10BE ||srcFormat AV_PIX_FMT_GBRAP12LE || srcFormat AV_PIX_FMT_GBRAP12BE ||srcFormat AV_PIX_FMT_GBRAP16LE || srcFormat AV_PIX_FMT_GBRAP16BE) (dstFormat AV_PIX_FMT_RGB48LE || dstFormat AV_PIX_FMT_RGB48BE ||dstFormat AV_PIX_FMT_BGR48LE || dstFormat AV_PIX_FMT_BGR48BE ||dstFormat AV_PIX_FMT_RGBA64LE || dstFormat AV_PIX_FMT_RGBA64BE ||dstFormat AV_PIX_FMT_BGRA64LE || dstFormat AV_PIX_FMT_BGRA64BE))c-convert_unscaled planarRgb16ToRgb16Wrapper;if (av_pix_fmt_desc_get(srcFormat)-comp[0].depth 8 isPackedRGB(srcFormat) dstFormat AV_PIX_FMT_GBRP)c-convert_unscaled rgbToPlanarRgbWrapper;if (isBayer(srcFormat)) {if (dstFormat AV_PIX_FMT_RGB24)c-convert_unscaled bayer_to_rgb24_wrapper;else if (dstFormat AV_PIX_FMT_RGB48)c-convert_unscaled bayer_to_rgb48_wrapper;else if (dstFormat AV_PIX_FMT_YUV420P)c-convert_unscaled bayer_to_yv12_wrapper;else if (!isBayer(dstFormat)) {av_log(c, AV_LOG_ERROR, unsupported bayer conversion\n);av_assert0(0);}}/* bswap 16 bits per pixel/component packed formats */if (IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BAYER_BGGR16) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BAYER_RGGB16) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BAYER_GBRG16) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BAYER_GRBG16) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BGR444) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BGR48) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BGR555) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BGR565) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_BGRA64) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GRAY9) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GRAY10) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GRAY12) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GRAY14) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GRAY16) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YA16) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_AYUV64) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRP9) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRP10) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRP12) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRP14) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRP16) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRAP10) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRAP12) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRAP16) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_RGB444) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_RGB48) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_RGB555) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_RGB565) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_RGBA64) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_XYZ12) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV420P9) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV420P10) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV420P12) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV420P14) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV420P16) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV422P9) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV422P10) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV422P12) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV422P14) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV422P16) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV440P10) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV440P12) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV444P9) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV444P10) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV444P12) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV444P14) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_YUV444P16))c-convert_unscaled bswap_16bpc;/* bswap 32 bits per pixel/component formats */if (IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRPF32) ||IS_DIFFERENT_ENDIANESS(srcFormat, dstFormat, AV_PIX_FMT_GBRAPF32))c-convert_unscaled bswap_32bpc;if (usePal(srcFormat) isByteRGB(dstFormat))c-convert_unscaled palToRgbWrapper;if (srcFormat AV_PIX_FMT_YUV422P) {if (dstFormat AV_PIX_FMT_YUYV422)c-convert_unscaled yuv422pToYuy2Wrapper;else if (dstFormat AV_PIX_FMT_UYVY422)c-convert_unscaled yuv422pToUyvyWrapper;}/* uint Y to float Y */if (srcFormat AV_PIX_FMT_GRAY8 dstFormat AV_PIX_FMT_GRAYF32){c-convert_unscaled uint_y_to_float_y_wrapper;}/* float Y to uint Y */if (srcFormat AV_PIX_FMT_GRAYF32 dstFormat AV_PIX_FMT_GRAY8){c-convert_unscaled float_y_to_uint_y_wrapper;}/* LQ converters if -sws 0 or -sws 4*/if (c-flags(SWS_FAST_BILINEAR|SWS_POINT)) {/* yv12_to_yuy2 */if (srcFormat AV_PIX_FMT_YUV420P || srcFormat AV_PIX_FMT_YUVA420P) {if (dstFormat AV_PIX_FMT_YUYV422)c-convert_unscaled planarToYuy2Wrapper;else if (dstFormat AV_PIX_FMT_UYVY422)c-convert_unscaled planarToUyvyWrapper;}}if (srcFormat AV_PIX_FMT_YUYV422 (dstFormat AV_PIX_FMT_YUV420P || dstFormat AV_PIX_FMT_YUVA420P))c-convert_unscaled yuyvToYuv420Wrapper;if (srcFormat AV_PIX_FMT_UYVY422 (dstFormat AV_PIX_FMT_YUV420P || dstFormat AV_PIX_FMT_YUVA420P))c-convert_unscaled uyvyToYuv420Wrapper;if (srcFormat AV_PIX_FMT_YUYV422 dstFormat AV_PIX_FMT_YUV422P)c-convert_unscaled yuyvToYuv422Wrapper;if (srcFormat AV_PIX_FMT_UYVY422 dstFormat AV_PIX_FMT_YUV422P)c-convert_unscaled uyvyToYuv422Wrapper;#define isPlanarGray(x) (isGray(x) (x) ! AV_PIX_FMT_YA8 (x) ! AV_PIX_FMT_YA16LE (x) ! AV_PIX_FMT_YA16BE)/* simple copy */if ( srcFormat dstFormat ||(srcFormat AV_PIX_FMT_YUVA420P dstFormat AV_PIX_FMT_YUV420P) ||(srcFormat AV_PIX_FMT_YUV420P dstFormat AV_PIX_FMT_YUVA420P) ||(isFloat(srcFormat) isFloat(dstFormat)) ((isPlanarYUV(srcFormat) isPlanarGray(dstFormat)) ||(isPlanarYUV(dstFormat) isPlanarGray(srcFormat)) ||(isPlanarGray(dstFormat) isPlanarGray(srcFormat)) ||(isPlanarYUV(srcFormat) isPlanarYUV(dstFormat) c-chrDstHSubSample c-chrSrcHSubSample c-chrDstVSubSample c-chrSrcVSubSample !isSemiPlanarYUV(srcFormat) !isSemiPlanarYUV(dstFormat)))){if (isPacked(c-srcFormat))c-convert_unscaled packedCopyWrapper;else /* Planar YUV or gray */c-convert_unscaled planarCopyWrapper;}if (ARCH_PPC)ff_get_unscaled_swscale_ppc(c);if (ARCH_ARM)ff_get_unscaled_swscale_arm(c);if (ARCH_AARCH64)ff_get_unscaled_swscale_aarch64(c);
}
从代码中可以看出它根据输入输出像素格式的不同选择了不同的转换函数。例如YUV420P转换NV12的时候就会将planarToNv12Wrapper()赋值给SwsContext的swscale指针。
有拉伸--swscale()
如果图像进行了拉伸则会调用ff_getSwsFunc()对SwsContext的swscale进行赋值。ff_getSwsFunc 函数被弃用参考链接FFmpeg源代码简单分析-其他-libswscale的sws_getContext()_MY CUP OF TEA的博客-CSDN博客ff_sws_init_scale函数的内部执行逻辑和 ff_getSwsFunc 类似
void ff_sws_init_scale(SwsContext *c)
{sws_init_swscale(c);if (ARCH_PPC)ff_sws_init_swscale_ppc(c);if (ARCH_X86)ff_sws_init_swscale_x86(c);if (ARCH_AARCH64)ff_sws_init_swscale_aarch64(c);if (ARCH_ARM)ff_sws_init_swscale_arm(c);
}
static av_cold void sws_init_swscale(SwsContext *c)
{enum AVPixelFormat srcFormat c-srcFormat;ff_sws_init_output_funcs(c, c-yuv2plane1, c-yuv2planeX,c-yuv2nv12cX, c-yuv2packed1,c-yuv2packed2, c-yuv2packedX, c-yuv2anyX);ff_sws_init_input_funcs(c);if (c-srcBpc 8) {if (c-dstBpc 14) {c-hyScale c-hcScale hScale8To15_c;if (c-flags SWS_FAST_BILINEAR) {c-hyscale_fast ff_hyscale_fast_c;c-hcscale_fast ff_hcscale_fast_c;}} else {c-hyScale c-hcScale hScale8To19_c;}} else {c-hyScale c-hcScale c-dstBpc 14 ? hScale16To19_c: hScale16To15_c;}ff_sws_init_range_convert(c);if (!(isGray(srcFormat) || isGray(c-dstFormat) ||srcFormat AV_PIX_FMT_MONOBLACK || srcFormat AV_PIX_FMT_MONOWHITE))c-needs_hcscale 1;
}未找到 代码依据注意sws_init_context()对SwsContext的swscale进行赋值的语句是c-swscale ff_getSwsFunc(c);即把ff_getSwsFunc()的返回值赋值给SwsContext的swscale指针而ff_getSwsFunc()的返回值是一个静态函数名称就叫做“swscale”。下面我们看一下这个swscale()静态函数的定义。
static int swscale(SwsContext *c, const uint8_t *src[],int srcStride[], int srcSliceY, int srcSliceH,uint8_t *dst[], int dstStride[],int dstSliceY, int dstSliceH)
{const int scale_dst dstSliceY 0 || dstSliceH c-dstH;/* load a few things into local vars to make the code more readable?* and faster */const int dstW c-dstW;int dstH c-dstH;const enum AVPixelFormat dstFormat c-dstFormat;const int flags c-flags;int32_t *vLumFilterPos c-vLumFilterPos;int32_t *vChrFilterPos c-vChrFilterPos;const int vLumFilterSize c-vLumFilterSize;const int vChrFilterSize c-vChrFilterSize;yuv2planar1_fn yuv2plane1 c-yuv2plane1;yuv2planarX_fn yuv2planeX c-yuv2planeX;yuv2interleavedX_fn yuv2nv12cX c-yuv2nv12cX;yuv2packed1_fn yuv2packed1 c-yuv2packed1;yuv2packed2_fn yuv2packed2 c-yuv2packed2;yuv2packedX_fn yuv2packedX c-yuv2packedX;yuv2anyX_fn yuv2anyX c-yuv2anyX;const int chrSrcSliceY srcSliceY c-chrSrcVSubSample;const int chrSrcSliceH AV_CEIL_RSHIFT(srcSliceH, c-chrSrcVSubSample);int should_dither isNBPS(c-srcFormat) ||is16BPS(c-srcFormat);int lastDstY;/* vars which will change and which we need to store back in the context */int dstY c-dstY;int lastInLumBuf c-lastInLumBuf;int lastInChrBuf c-lastInChrBuf;int lumStart 0;int lumEnd c-descIndex[0];int chrStart lumEnd;int chrEnd c-descIndex[1];int vStart chrEnd;int vEnd c-numDesc;SwsSlice *src_slice c-slice[lumStart];SwsSlice *hout_slice c-slice[c-numSlice-2];SwsSlice *vout_slice c-slice[c-numSlice-1];SwsFilterDescriptor *desc c-desc;int needAlpha c-needAlpha;int hasLumHoles 1;int hasChrHoles 1;if (isPacked(c-srcFormat)) {src[1] src[2] src[3] src[0];srcStride[1] srcStride[2] srcStride[3] srcStride[0];}srcStride[1] * 1 c-vChrDrop;srcStride[2] * 1 c-vChrDrop;DEBUG_BUFFERS(swscale() %p[%d] %p[%d] %p[%d] %p[%d] - %p[%d] %p[%d] %p[%d] %p[%d]\n,src[0], srcStride[0], src[1], srcStride[1],src[2], srcStride[2], src[3], srcStride[3],dst[0], dstStride[0], dst[1], dstStride[1],dst[2], dstStride[2], dst[3], dstStride[3]);DEBUG_BUFFERS(srcSliceY: %d srcSliceH: %d dstY: %d dstH: %d\n,srcSliceY, srcSliceH, dstY, dstH);DEBUG_BUFFERS(vLumFilterSize: %d vChrFilterSize: %d\n,vLumFilterSize, vChrFilterSize);if (dstStride[0]15 || dstStride[1]15 ||dstStride[2]15 || dstStride[3]15) {SwsContext *const ctx c-parent ? c-parent : c;if (flags SWS_PRINT_INFO !atomic_exchange_explicit(ctx-stride_unaligned_warned, 1, memory_order_relaxed)) {av_log(c, AV_LOG_WARNING,Warning: dstStride is not aligned!\n -cannot do aligned memory accesses anymore\n);}}#if ARCH_X86if ( (uintptr_t)dst[0]15 || (uintptr_t)dst[1]15 || (uintptr_t)dst[2]15|| (uintptr_t)src[0]15 || (uintptr_t)src[1]15 || (uintptr_t)src[2]15|| dstStride[0]15 || dstStride[1]15 || dstStride[2]15 || dstStride[3]15|| srcStride[0]15 || srcStride[1]15 || srcStride[2]15 || srcStride[3]15) {SwsContext *const ctx c-parent ? c-parent : c;int cpu_flags av_get_cpu_flags();if (flags SWS_PRINT_INFO HAVE_MMXEXT (cpu_flags AV_CPU_FLAG_SSE2) !atomic_exchange_explicit(ctx-stride_unaligned_warned,1, memory_order_relaxed)) {av_log(c, AV_LOG_WARNING, Warning: data is not aligned! This can lead to a speed loss\n);}}
#endifif (scale_dst) {dstY dstSliceY;dstH dstY dstSliceH;lastInLumBuf -1;lastInChrBuf -1;} else if (srcSliceY 0) {/* Note the user might start scaling the picture in the middle so this* will not get executed. This is not really intended but works* currently, so people might do it. */dstY 0;lastInLumBuf -1;lastInChrBuf -1;}if (!should_dither) {c-chrDither8 c-lumDither8 sws_pb_64;}lastDstY dstY;ff_init_vscale_pfn(c, yuv2plane1, yuv2planeX, yuv2nv12cX,yuv2packed1, yuv2packed2, yuv2packedX, yuv2anyX, c-use_mmx_vfilter);ff_init_slice_from_src(src_slice, (uint8_t**)src, srcStride, c-srcW,srcSliceY, srcSliceH, chrSrcSliceY, chrSrcSliceH, 1);ff_init_slice_from_src(vout_slice, (uint8_t**)dst, dstStride, c-dstW,dstY, dstSliceH, dstY c-chrDstVSubSample,AV_CEIL_RSHIFT(dstSliceH, c-chrDstVSubSample), scale_dst);if (srcSliceY 0) {hout_slice-plane[0].sliceY lastInLumBuf 1;hout_slice-plane[1].sliceY lastInChrBuf 1;hout_slice-plane[2].sliceY lastInChrBuf 1;hout_slice-plane[3].sliceY lastInLumBuf 1;hout_slice-plane[0].sliceH hout_slice-plane[1].sliceH hout_slice-plane[2].sliceH hout_slice-plane[3].sliceH 0;hout_slice-width dstW;}for (; dstY dstH; dstY) {const int chrDstY dstY c-chrDstVSubSample;int use_mmx_vfilter c-use_mmx_vfilter;// First line needed as inputconst int firstLumSrcY FFMAX(1 - vLumFilterSize, vLumFilterPos[dstY]);const int firstLumSrcY2 FFMAX(1 - vLumFilterSize, vLumFilterPos[FFMIN(dstY | ((1 c-chrDstVSubSample) - 1), c-dstH - 1)]);// First line needed as inputconst int firstChrSrcY FFMAX(1 - vChrFilterSize, vChrFilterPos[chrDstY]);// Last line needed as inputint lastLumSrcY FFMIN(c-srcH, firstLumSrcY vLumFilterSize) - 1;int lastLumSrcY2 FFMIN(c-srcH, firstLumSrcY2 vLumFilterSize) - 1;int lastChrSrcY FFMIN(c-chrSrcH, firstChrSrcY vChrFilterSize) - 1;int enough_lines;int i;int posY, cPosY, firstPosY, lastPosY, firstCPosY, lastCPosY;// handle holes (FAST_BILINEAR weird filters)if (firstLumSrcY lastInLumBuf) {hasLumHoles lastInLumBuf ! firstLumSrcY - 1;if (hasLumHoles) {hout_slice-plane[0].sliceY firstLumSrcY;hout_slice-plane[3].sliceY firstLumSrcY;hout_slice-plane[0].sliceH hout_slice-plane[3].sliceH 0;}lastInLumBuf firstLumSrcY - 1;}if (firstChrSrcY lastInChrBuf) {hasChrHoles lastInChrBuf ! firstChrSrcY - 1;if (hasChrHoles) {hout_slice-plane[1].sliceY firstChrSrcY;hout_slice-plane[2].sliceY firstChrSrcY;hout_slice-plane[1].sliceH hout_slice-plane[2].sliceH 0;}lastInChrBuf firstChrSrcY - 1;}DEBUG_BUFFERS(dstY: %d\n, dstY);DEBUG_BUFFERS(\tfirstLumSrcY: %d lastLumSrcY: %d lastInLumBuf: %d\n,firstLumSrcY, lastLumSrcY, lastInLumBuf);DEBUG_BUFFERS(\tfirstChrSrcY: %d lastChrSrcY: %d lastInChrBuf: %d\n,firstChrSrcY, lastChrSrcY, lastInChrBuf);// Do we have enough lines in this slice to output the dstY lineenough_lines lastLumSrcY2 srcSliceY srcSliceH lastChrSrcY AV_CEIL_RSHIFT(srcSliceY srcSliceH, c-chrSrcVSubSample);if (!enough_lines) {lastLumSrcY srcSliceY srcSliceH - 1;lastChrSrcY chrSrcSliceY chrSrcSliceH - 1;DEBUG_BUFFERS(buffering slice: lastLumSrcY %d lastChrSrcY %d\n,lastLumSrcY, lastChrSrcY);}av_assert0((lastLumSrcY - firstLumSrcY 1) hout_slice-plane[0].available_lines);av_assert0((lastChrSrcY - firstChrSrcY 1) hout_slice-plane[1].available_lines);posY hout_slice-plane[0].sliceY hout_slice-plane[0].sliceH;if (posY lastLumSrcY !hasLumHoles) {firstPosY FFMAX(firstLumSrcY, posY);lastPosY FFMIN(firstLumSrcY hout_slice-plane[0].available_lines - 1, srcSliceY srcSliceH - 1);} else {firstPosY posY;lastPosY lastLumSrcY;}cPosY hout_slice-plane[1].sliceY hout_slice-plane[1].sliceH;if (cPosY lastChrSrcY !hasChrHoles) {firstCPosY FFMAX(firstChrSrcY, cPosY);lastCPosY FFMIN(firstChrSrcY hout_slice-plane[1].available_lines - 1, AV_CEIL_RSHIFT(srcSliceY srcSliceH, c-chrSrcVSubSample) - 1);} else {firstCPosY cPosY;lastCPosY lastChrSrcY;}ff_rotate_slice(hout_slice, lastPosY, lastCPosY);if (posY lastLumSrcY 1) {for (i lumStart; i lumEnd; i)desc[i].process(c, desc[i], firstPosY, lastPosY - firstPosY 1);}lastInLumBuf lastLumSrcY;if (cPosY lastChrSrcY 1) {for (i chrStart; i chrEnd; i)desc[i].process(c, desc[i], firstCPosY, lastCPosY - firstCPosY 1);}lastInChrBuf lastChrSrcY;if (!enough_lines)break; // we cant output a dstY line so lets try with the next slice#if HAVE_MMX_INLINEff_updateMMXDitherTables(c, dstY);
#endifif (should_dither) {c-chrDither8 ff_dither_8x8_128[chrDstY 7];c-lumDither8 ff_dither_8x8_128[dstY 7];}if (dstY c-dstH - 2) {/* hmm looks like we cant use MMX here without overwriting* this arrays tail */ff_sws_init_output_funcs(c, yuv2plane1, yuv2planeX, yuv2nv12cX,yuv2packed1, yuv2packed2, yuv2packedX, yuv2anyX);use_mmx_vfilter 0;ff_init_vscale_pfn(c, yuv2plane1, yuv2planeX, yuv2nv12cX,yuv2packed1, yuv2packed2, yuv2packedX, yuv2anyX, use_mmx_vfilter);}for (i vStart; i vEnd; i)desc[i].process(c, desc[i], dstY, 1);}if (isPlanar(dstFormat) isALPHA(dstFormat) !needAlpha) {int offset lastDstY - dstSliceY;int length dstW;int height dstY - lastDstY;if (is16BPS(dstFormat) || isNBPS(dstFormat)) {const AVPixFmtDescriptor *desc av_pix_fmt_desc_get(dstFormat);fillPlane16(dst[3], dstStride[3], length, height, offset,1, desc-comp[3].depth,isBE(dstFormat));} else if (is32BPS(dstFormat)) {const AVPixFmtDescriptor *desc av_pix_fmt_desc_get(dstFormat);fillPlane32(dst[3], dstStride[3], length, height, offset,1, desc-comp[3].depth,isBE(dstFormat), desc-flags AV_PIX_FMT_FLAG_FLOAT);} elsefillPlane(dst[3], dstStride[3], length, height, offset, 255);}#if HAVE_MMXEXT_INLINEif (av_get_cpu_flags() AV_CPU_FLAG_MMXEXT)__asm__ volatile (sfence ::: memory);
#endifemms_c();/* store changed local vars back in the context */c-dstY dstY;c-lastInLumBuf lastInLumBuf;c-lastInChrBuf lastInChrBuf;return dstY - lastDstY;
}可以看出swscale()是一行一行的进行图像缩放工作的。其中每行数据的处理按照“先水平拉伸然后垂直拉伸”的方式进行处理。具体的实现函数如下所示1. 水平拉伸 a) 亮度水平拉伸hyscale()b) 色度水平拉伸hcscale()2. 垂直拉伸a) Planar i. 亮度垂直拉伸-不拉伸yuv2plane1()ii. 亮度垂直拉伸-拉伸yuv2planeX()iii. 色度垂直拉伸-不拉伸yuv2plane1()iv. 色度垂直拉伸-拉伸yuv2planeX()b) Packed i. 垂直拉伸-不拉伸yuv2packed1()ii. 垂直拉伸-拉伸yuv2packedX()下面具体看看这几个函数的定义。
hyscale()
水平亮度拉伸函数hyscale()的定义位于libswscale\swscale.c如下所示。 并不存在/*** Scale one horizontal line of input data using a filter over the input* lines, to produce one (differently sized) line of output data.** param dst pointer to destination buffer for horizontally scaled* data. If the number of bits per component of one* destination pixel (SwsContext-dstBpc) is 10, data* will be 15 bpc in 16 bits (int16_t) width. Else (i.e.* SwsContext-dstBpc 16), data will be 19bpc in* 32 bits (int32_t) width.* param dstW width of destination image* param src pointer to source data to be scaled. If the number of* bits per component of a source pixel (SwsContext-srcBpc)* is 8, this is 8bpc in 8 bits (uint8_t) width. Else* (i.e. SwsContext-dstBpc 8), this is native depth* in 16 bits (uint16_t) width. In other words, for 9-bit* YUV input, this is 9bpc, for 10-bit YUV input, this is* 10bpc, and for 16-bit RGB or YUV, this is 16bpc.* param filter filter coefficients to be used per output pixel for* scaling. This contains 14bpp filtering coefficients.* Guaranteed to contain dstW * filterSize entries.* param filterPos position of the first input pixel to be used for* each output pixel during scaling. Guaranteed to* contain dstW entries.* param filterSize the number of input coefficients to be used (and* thus the number of input pixels to be used) for* creating a single output pixel. Is aligned to 4* (and input coefficients thus padded with zeroes)* to simplify creating SIMD code.*//** { */void (*hyScale)(struct SwsContext *c, int16_t *dst, int dstW,const uint8_t *src, const int16_t *filter,const int32_t *filterPos, int filterSize);void (*hcScale)(struct SwsContext *c, int16_t *dst, int dstW,const uint8_t *src, const int16_t *filter,const int32_t *filterPos, int filterSize);
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