avcodec const correctness patch by (Drew Hess <dhess at ilm dot com>)

Originally committed as revision 2318 to svn://svn.ffmpeg.org/ffmpeg/trunk

4 files changed, 85 insertions, 70 deletions

diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index 29304bac89..4822e87d1a 100644
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -520,7 +520,7 @@ typedef struct AVCodecContext {
      * @param offset offset into the AVFrame.data from which the slice should be read
      */
     void (*draw_horiz_band)(struct AVCodecContext *s,
-                            AVFrame *src, int offset[4],
+                            const AVFrame *src, int offset[4],
                             int y, int type, int height);
 
     /* audio only */
@@ -1483,13 +1483,13 @@ ImgReSampleContext *img_resample_full_init(int owidth, int oheight,
                                       int leftBand, int rightBand);
 
 void img_resample(ImgReSampleContext *s, 
-                  AVPicture *output, AVPicture *input);
+                  AVPicture *output, const AVPicture *input);
 
 void img_resample_close(ImgReSampleContext *s);
 
 int avpicture_fill(AVPicture *picture, uint8_t *ptr,
                    int pix_fmt, int width, int height);
-int avpicture_layout(AVPicture* src, int pix_fmt, int width, int height,
+int avpicture_layout(const AVPicture* src, int pix_fmt, int width, int height,
                      unsigned char *dest, int dest_size);
 int avpicture_get_size(int pix_fmt, int width, int height);
 void avcodec_get_chroma_sub_sample(int pix_fmt, int *h_shift, int *v_shift);
@@ -1510,15 +1510,16 @@ int avcodec_find_best_pix_fmt(int pix_fmt_mask, int src_pix_fmt,
 
 #define FF_ALPHA_TRANSP       0x0001 /* image has some totally transparent pixels */
 #define FF_ALPHA_SEMI_TRANSP  0x0002 /* image has some transparent pixels */
-int img_get_alpha_info(AVPicture *src, int pix_fmt, int width, int height);
+int img_get_alpha_info(const AVPicture *src,
+		       int pix_fmt, int width, int height);
 
 /* convert among pixel formats */
 int img_convert(AVPicture *dst, int dst_pix_fmt,
-                AVPicture *src, int pix_fmt, 
+                const AVPicture *src, int pix_fmt, 
                 int width, int height);
 
 /* deinterlace a picture */
-int avpicture_deinterlace(AVPicture *dst, AVPicture *src,
+int avpicture_deinterlace(AVPicture *dst, const AVPicture *src,
                           int pix_fmt, int width, int height);
 
 /* external high level API */
diff --git a/libavcodec/imgconvert.c b/libavcodec/imgconvert.c
index 6324576472..98ab7d53d6 100644
--- a/libavcodec/imgconvert.c
+++ b/libavcodec/imgconvert.c
@@ -236,7 +236,7 @@ enum PixelFormat avcodec_get_pix_fmt(const char* name)
 
 /* Picture field are filled with 'ptr' addresses. Also return size */
 int avpicture_fill(AVPicture *picture, uint8_t *ptr,
-                   int pix_fmt, int width, int height)
+		   int pix_fmt, int width, int height)
 {
     int size, w2, h2, size2;
     PixFmtInfo *pinfo;
@@ -313,12 +313,12 @@ int avpicture_fill(AVPicture *picture, uint8_t *ptr,
     }
 }
 
-int avpicture_layout(AVPicture* src, int pix_fmt, int width, int height,
+int avpicture_layout(const AVPicture* src, int pix_fmt, int width, int height,
                      unsigned char *dest, int dest_size)
 {
     PixFmtInfo* pf = &pix_fmt_info[pix_fmt];
     int i, j, w, h, data_planes;
-    unsigned char* s; 
+    const unsigned char* s; 
     int size = avpicture_get_size(pix_fmt, width, height);
 
     if (size > dest_size)
@@ -535,7 +535,7 @@ static void img_copy_plane(uint8_t *dst, int dst_wrap,
 /**
  * Copy image 'src' to 'dst'.
  */
-void img_copy(AVPicture *dst, AVPicture *src,
+void img_copy(AVPicture *dst, const AVPicture *src,
               int pix_fmt, int width, int height)
 {
     int bwidth, bits, i;
@@ -588,7 +588,7 @@ void img_copy(AVPicture *dst, AVPicture *src,
 
 /* XXX: totally non optimized */
 
-static void yuv422_to_yuv420p(AVPicture *dst, AVPicture *src,
+static void yuv422_to_yuv420p(AVPicture *dst, const AVPicture *src,
                               int width, int height)
 {
     const uint8_t *p, *p1;
@@ -644,7 +644,7 @@ static void yuv422_to_yuv420p(AVPicture *dst, AVPicture *src,
     }
 }
 
-static void yuv422_to_yuv422p(AVPicture *dst, AVPicture *src,
+static void yuv422_to_yuv422p(AVPicture *dst, const AVPicture *src,
                               int width, int height)
 {
     const uint8_t *p, *p1;
@@ -677,7 +677,7 @@ static void yuv422_to_yuv422p(AVPicture *dst, AVPicture *src,
     }
 }
 
-static void yuv422p_to_yuv422(AVPicture *dst, AVPicture *src,
+static void yuv422p_to_yuv422(AVPicture *dst, const AVPicture *src,
                               int width, int height)
 {
     uint8_t *p, *p1;
@@ -1286,7 +1286,7 @@ static inline unsigned int bitcopy_n(unsigned int a, int n)
 
 #include "imgconvert_template.h"
 
-static void mono_to_gray(AVPicture *dst, AVPicture *src,
+static void mono_to_gray(AVPicture *dst, const AVPicture *src,
                          int width, int height, int xor_mask)
 {
     const unsigned char *p;
@@ -1327,19 +1327,19 @@ static void mono_to_gray(AVPicture *dst, AVPicture *src,
     }
 }
 
-static void monowhite_to_gray(AVPicture *dst, AVPicture *src,
+static void monowhite_to_gray(AVPicture *dst, const AVPicture *src,
                                int width, int height)
 {
     mono_to_gray(dst, src, width, height, 0xff);
 }
 
-static void monoblack_to_gray(AVPicture *dst, AVPicture *src,
+static void monoblack_to_gray(AVPicture *dst, const AVPicture *src,
                                int width, int height)
 {
     mono_to_gray(dst, src, width, height, 0x00);
 }
 
-static void gray_to_mono(AVPicture *dst, AVPicture *src,
+static void gray_to_mono(AVPicture *dst, const AVPicture *src,
                          int width, int height, int xor_mask)
 {
     int n;
@@ -1383,20 +1383,21 @@ static void gray_to_mono(AVPicture *dst, AVPicture *src,
     }
 }
 
-static void gray_to_monowhite(AVPicture *dst, AVPicture *src,
+static void gray_to_monowhite(AVPicture *dst, const AVPicture *src,
                               int width, int height)
 {
     gray_to_mono(dst, src, width, height, 0xff);
 }
 
-static void gray_to_monoblack(AVPicture *dst, AVPicture *src,
+static void gray_to_monoblack(AVPicture *dst, const AVPicture *src,
                               int width, int height)
 {
     gray_to_mono(dst, src, width, height, 0x00);
 }
 
 typedef struct ConvertEntry {
-    void (*convert)(AVPicture *dst, AVPicture *src, int width, int height);
+    void (*convert)(AVPicture *dst,
+		    const AVPicture *src, int width, int height);
 } ConvertEntry;
 
 /* Add each new convertion function in this table. In order to be able
@@ -1644,7 +1645,7 @@ static inline int is_yuv_planar(PixFmtInfo *ps)
 
 /* XXX: always use linesize. Return -1 if not supported */
 int img_convert(AVPicture *dst, int dst_pix_fmt,
-                AVPicture *src, int src_pix_fmt, 
+                const AVPicture *src, int src_pix_fmt, 
                 int src_width, int src_height)
 {
     static int inited;
@@ -1877,7 +1878,7 @@ int img_convert(AVPicture *dst, int dst_pix_fmt,
 }
 
 /* NOTE: we scan all the pixels to have an exact information */
-static int get_alpha_info_pal8(AVPicture *src, int width, int height)
+static int get_alpha_info_pal8(const AVPicture *src, int width, int height)
 {
     const unsigned char *p;
     int src_wrap, ret, x, y;
@@ -1906,7 +1907,8 @@ static int get_alpha_info_pal8(AVPicture *src, int width, int height)
  * Tell if an image really has transparent alpha values.
  * @return ored mask of FF_ALPHA_xxx constants
  */
-int img_get_alpha_info(AVPicture *src, int pix_fmt, int width, int height)
+int img_get_alpha_info(const AVPicture *src,
+		       int pix_fmt, int width, int height)
 {
     PixFmtInfo *pf = &pix_fmt_info[pix_fmt];
     int ret;
@@ -1981,8 +1983,11 @@ int img_get_alpha_info(AVPicture *src, int pix_fmt, int width, int height)
 #endif
 
 /* filter parameters: [-1 4 2 4 -1] // 8 */
-static void deinterlace_line(uint8_t *dst, uint8_t *lum_m4, uint8_t *lum_m3, uint8_t *lum_m2, uint8_t *lum_m1, uint8_t *lum,
-                                int size)
+static void deinterlace_line(uint8_t *dst, 
+			     const uint8_t *lum_m4, const uint8_t *lum_m3, 
+			     const uint8_t *lum_m2, const uint8_t *lum_m1, 
+			     const uint8_t *lum,
+			     int size)
 {
 #ifndef HAVE_MMX
     uint8_t *cm = cropTbl + MAX_NEG_CROP;
@@ -2071,10 +2076,10 @@ static void deinterlace_line_inplace(uint8_t *lum_m4, uint8_t *lum_m3, uint8_t *
    top field is copied as is, but the bottom field is deinterlaced
    against the top field. */
 static void deinterlace_bottom_field(uint8_t *dst, int dst_wrap,
-                                    uint8_t *src1, int src_wrap,
+                                    const uint8_t *src1, int src_wrap,
                                     int width, int height)
 {
-    uint8_t *src_m2, *src_m1, *src_0, *src_p1, *src_p2;
+    const uint8_t *src_m2, *src_m1, *src_0, *src_p1, *src_p2;
     int y;
 
     src_m2 = src1;
@@ -2100,7 +2105,7 @@ static void deinterlace_bottom_field(uint8_t *dst, int dst_wrap,
 }
 
 static void deinterlace_bottom_field_inplace(uint8_t *src1, int src_wrap,
-                                     int width, int height)
+					     int width, int height)
 {
     uint8_t *src_m1, *src_0, *src_p1, *src_p2;
     int y;
@@ -2126,7 +2131,7 @@ static void deinterlace_bottom_field_inplace(uint8_t *src1, int src_wrap,
 
 
 /* deinterlace - if not supported return -1 */
-int avpicture_deinterlace(AVPicture *dst, AVPicture *src,
+int avpicture_deinterlace(AVPicture *dst, const AVPicture *src,
                           int pix_fmt, int width, int height)
 {
     int i;
@@ -2157,7 +2162,7 @@ int avpicture_deinterlace(AVPicture *dst, AVPicture *src,
             }
         }
         if (src == dst) {
-            deinterlace_bottom_field_inplace(src->data[i], src->linesize[i],
+            deinterlace_bottom_field_inplace(dst->data[i], dst->linesize[i],
                                  width, height);
         } else {
             deinterlace_bottom_field(dst->data[i],dst->linesize[i],
diff --git a/libavcodec/imgconvert_template.h b/libavcodec/imgconvert_template.h
index 015b74f1e3..cd5a7313c3 100644
--- a/libavcodec/imgconvert_template.h
+++ b/libavcodec/imgconvert_template.h
@@ -21,10 +21,11 @@
 #define RGB_OUT(d, r, g, b) RGBA_OUT(d, r, g, b, 0xff)
 #endif
 
-static void glue(yuv420p_to_, RGB_NAME)(AVPicture *dst, AVPicture *src,
+static void glue(yuv420p_to_, RGB_NAME)(AVPicture *dst, const AVPicture *src,
                                         int width, int height)
 {
-    uint8_t *y1_ptr, *y2_ptr, *cb_ptr, *cr_ptr, *d, *d1, *d2;
+    const uint8_t *y1_ptr, *y2_ptr, *cb_ptr, *cr_ptr;
+    uint8_t *d, *d1, *d2;
     int w, y, cb, cr, r_add, g_add, b_add, width2;
     uint8_t *cm = cropTbl + MAX_NEG_CROP;
     unsigned int r, g, b;
@@ -114,10 +115,11 @@ static void glue(yuv420p_to_, RGB_NAME)(AVPicture *dst, AVPicture *src,
     }
 }
 
-static void glue(yuvj420p_to_, RGB_NAME)(AVPicture *dst, AVPicture *src,
+static void glue(yuvj420p_to_, RGB_NAME)(AVPicture *dst, const AVPicture *src,
                                          int width, int height)
 {
-    uint8_t *y1_ptr, *y2_ptr, *cb_ptr, *cr_ptr, *d, *d1, *d2;
+    const uint8_t *y1_ptr, *y2_ptr, *cb_ptr, *cr_ptr;
+    uint8_t *d, *d1, *d2;
     int w, y, cb, cr, r_add, g_add, b_add, width2;
     uint8_t *cm = cropTbl + MAX_NEG_CROP;
     unsigned int r, g, b;
@@ -207,7 +209,7 @@ static void glue(yuvj420p_to_, RGB_NAME)(AVPicture *dst, AVPicture *src,
     }
 }
 
-static void glue(RGB_NAME, _to_yuv420p)(AVPicture *dst, AVPicture *src,
+static void glue(RGB_NAME, _to_yuv420p)(AVPicture *dst, const AVPicture *src,
                                         int width, int height)
 {
     int wrap, wrap3, width2;
@@ -314,7 +316,7 @@ static void glue(RGB_NAME, _to_yuv420p)(AVPicture *dst, AVPicture *src,
     }
 }
 
-static void glue(RGB_NAME, _to_gray)(AVPicture *dst, AVPicture *src,
+static void glue(RGB_NAME, _to_gray)(AVPicture *dst, const AVPicture *src,
                                      int width, int height)
 {
     const unsigned char *p;
@@ -340,7 +342,7 @@ static void glue(RGB_NAME, _to_gray)(AVPicture *dst, AVPicture *src,
     }
 }
 
-static void glue(gray_to_, RGB_NAME)(AVPicture *dst, AVPicture *src,
+static void glue(gray_to_, RGB_NAME)(AVPicture *dst, const AVPicture *src,
                                      int width, int height)
 {
     const unsigned char *p;
@@ -366,7 +368,7 @@ static void glue(gray_to_, RGB_NAME)(AVPicture *dst, AVPicture *src,
     }
 }
 
-static void glue(pal8_to_, RGB_NAME)(AVPicture *dst, AVPicture *src,
+static void glue(pal8_to_, RGB_NAME)(AVPicture *dst, const AVPicture *src,
                                      int width, int height)
 {
     const unsigned char *p;
@@ -409,7 +411,7 @@ static void glue(pal8_to_, RGB_NAME)(AVPicture *dst, AVPicture *src,
 #if !defined(FMT_RGBA32) && defined(RGBA_OUT)
 /* alpha support */
 
-static void glue(rgba32_to_, RGB_NAME)(AVPicture *dst, AVPicture *src,
+static void glue(rgba32_to_, RGB_NAME)(AVPicture *dst, const AVPicture *src,
                                       int width, int height)
 {
     const uint8_t *s;
@@ -439,7 +441,7 @@ static void glue(rgba32_to_, RGB_NAME)(AVPicture *dst, AVPicture *src,
     }
 }
 
-static void glue(RGB_NAME, _to_rgba32)(AVPicture *dst, AVPicture *src,
+static void glue(RGB_NAME, _to_rgba32)(AVPicture *dst, const AVPicture *src,
                                        int width, int height)
 {
     const uint8_t *s;
@@ -469,7 +471,7 @@ static void glue(RGB_NAME, _to_rgba32)(AVPicture *dst, AVPicture *src,
 
 #ifndef FMT_RGB24
 
-static void glue(rgb24_to_, RGB_NAME)(AVPicture *dst, AVPicture *src,
+static void glue(rgb24_to_, RGB_NAME)(AVPicture *dst, const AVPicture *src,
                                       int width, int height)
 {
     const uint8_t *s;
@@ -497,7 +499,7 @@ static void glue(rgb24_to_, RGB_NAME)(AVPicture *dst, AVPicture *src,
     }
 }
 
-static void glue(RGB_NAME, _to_rgb24)(AVPicture *dst, AVPicture *src,
+static void glue(RGB_NAME, _to_rgb24)(AVPicture *dst, const AVPicture *src,
                                       int width, int height)
 {
     const uint8_t *s;
@@ -529,10 +531,11 @@ static void glue(RGB_NAME, _to_rgb24)(AVPicture *dst, AVPicture *src,
 
 #ifdef FMT_RGB24
 
-static void yuv444p_to_rgb24(AVPicture *dst, AVPicture *src,
+static void yuv444p_to_rgb24(AVPicture *dst, const AVPicture *src,
                              int width, int height)
 {
-    uint8_t *y1_ptr, *cb_ptr, *cr_ptr, *d, *d1;
+    const uint8_t *y1_ptr, *cb_ptr, *cr_ptr;
+    uint8_t *d, *d1;
     int w, y, cb, cr, r_add, g_add, b_add;
     uint8_t *cm = cropTbl + MAX_NEG_CROP;
     unsigned int r, g, b;
@@ -561,10 +564,11 @@ static void yuv444p_to_rgb24(AVPicture *dst, AVPicture *src,
     }
 }
 
-static void yuvj444p_to_rgb24(AVPicture *dst, AVPicture *src,
+static void yuvj444p_to_rgb24(AVPicture *dst, const AVPicture *src,
                               int width, int height)
 {
-    uint8_t *y1_ptr, *cb_ptr, *cr_ptr, *d, *d1;
+    const uint8_t *y1_ptr, *cb_ptr, *cr_ptr;
+    uint8_t *d, *d1;
     int w, y, cb, cr, r_add, g_add, b_add;
     uint8_t *cm = cropTbl + MAX_NEG_CROP;
     unsigned int r, g, b;
@@ -593,7 +597,7 @@ static void yuvj444p_to_rgb24(AVPicture *dst, AVPicture *src,
     }
 }
 
-static void rgb24_to_yuv444p(AVPicture *dst, AVPicture *src,
+static void rgb24_to_yuv444p(AVPicture *dst, const AVPicture *src,
                              int width, int height)
 {
     int src_wrap, x, y;
@@ -625,7 +629,7 @@ static void rgb24_to_yuv444p(AVPicture *dst, AVPicture *src,
     }
 }
 
-static void rgb24_to_yuvj420p(AVPicture *dst, AVPicture *src,
+static void rgb24_to_yuvj420p(AVPicture *dst, const AVPicture *src,
                               int width, int height)
 {
     int wrap, wrap3, width2;
@@ -732,7 +736,7 @@ static void rgb24_to_yuvj420p(AVPicture *dst, AVPicture *src,
     }
 }
 
-static void rgb24_to_yuvj444p(AVPicture *dst, AVPicture *src,
+static void rgb24_to_yuvj444p(AVPicture *dst, const AVPicture *src,
                               int width, int height)
 {
     int src_wrap, x, y;
@@ -768,7 +772,7 @@ static void rgb24_to_yuvj444p(AVPicture *dst, AVPicture *src,
 
 #if defined(FMT_RGB24) || defined(FMT_RGBA32)
 
-static void glue(RGB_NAME, _to_pal8)(AVPicture *dst, AVPicture *src,
+static void glue(RGB_NAME, _to_pal8)(AVPicture *dst, const AVPicture *src,
                                      int width, int height)
 {
     const unsigned char *p;
@@ -816,7 +820,8 @@ static void glue(RGB_NAME, _to_pal8)(AVPicture *dst, AVPicture *src,
         
 #ifdef RGBA_IN
 
-static int glue(get_alpha_info_, RGB_NAME)(AVPicture *src, int width, int height)
+static int glue(get_alpha_info_, RGB_NAME)(const AVPicture *src,
+					   int width, int height)
 {
     const unsigned char *p;
     int src_wrap, ret, x, y;
diff --git a/libavcodec/imgresample.c b/libavcodec/imgresample.c
index 140894d365..a18645e33e 100644
--- a/libavcodec/imgresample.c
+++ b/libavcodec/imgresample.c
@@ -58,11 +58,12 @@ static inline int get_phase(int pos)
 }
 
 /* This function must be optimized */
-static void h_resample_fast(uint8_t *dst, int dst_width, uint8_t *src, int src_width,
-                            int src_start, int src_incr, int16_t *filters)
+static void h_resample_fast(uint8_t *dst, int dst_width, const uint8_t *src,
+			    int src_width, int src_start, int src_incr,
+			    int16_t *filters)
 {
     int src_pos, phase, sum, i;
-    uint8_t *s;
+    const uint8_t *s;
     int16_t *filter;
 
     src_pos = src_start;
@@ -101,11 +102,11 @@ static void h_resample_fast(uint8_t *dst, int dst_width, uint8_t *src, int src_w
 }
 
 /* This function must be optimized */
-static void v_resample(uint8_t *dst, int dst_width, uint8_t *src, int wrap, 
-                       int16_t *filter)
+static void v_resample(uint8_t *dst, int dst_width, const uint8_t *src,
+		       int wrap, int16_t *filter)
 {
     int sum, i;
-    uint8_t *s;
+    const uint8_t *s;
 
     s = src;
     for(i=0;i<dst_width;i++) {
@@ -160,11 +161,12 @@ static void v_resample(uint8_t *dst, int dst_width, uint8_t *src, int wrap,
 #define DUMP(reg) movq_r2m(reg, tmp); printf(#reg "=%016Lx\n", tmp.uq);
 
 /* XXX: do four pixels at a time */
-static void h_resample_fast4_mmx(uint8_t *dst, int dst_width, uint8_t *src, int src_width,
+static void h_resample_fast4_mmx(uint8_t *dst, int dst_width,
+				 const uint8_t *src, int src_width,
                                  int src_start, int src_incr, int16_t *filters)
 {
     int src_pos, phase;
-    uint8_t *s;
+    const uint8_t *s;
     int16_t *filter;
     mmx_t tmp;
     
@@ -204,11 +206,11 @@ static void h_resample_fast4_mmx(uint8_t *dst, int dst_width, uint8_t *src, int
     emms();
 }
 
-static void v_resample4_mmx(uint8_t *dst, int dst_width, uint8_t *src, int wrap, 
-                            int16_t *filter)
+static void v_resample4_mmx(uint8_t *dst, int dst_width, const uint8_t *src,
+			    int wrap, int16_t *filter)
 {
     int sum, i, v;
-    uint8_t *s;
+    const uint8_t *s;
     mmx_t tmp;
     mmx_t coefs[4];
     
@@ -280,11 +282,11 @@ typedef	union {
     signed short s[8];
 } vec_ss_t;
 
-void v_resample16_altivec(uint8_t *dst, int dst_width, uint8_t *src, int wrap,
-                            int16_t *filter)
+void v_resample16_altivec(uint8_t *dst, int dst_width, const uint8_t *src,
+			  int wrap, int16_t *filter)
 {
     int sum, i;
-    uint8_t *s;
+    const uint8_t *s;
     vector unsigned char *tv, tmp, dstv, zero;
     vec_ss_t srchv[4], srclv[4], fv[4];
     vector signed short zeros, sumhv, sumlv;    
@@ -397,11 +399,12 @@ void v_resample16_altivec(uint8_t *dst, int dst_width, uint8_t *src, int wrap,
 #endif
 
 /* slow version to handle limit cases. Does not need optimisation */
-static void h_resample_slow(uint8_t *dst, int dst_width, uint8_t *src, int src_width,
+static void h_resample_slow(uint8_t *dst, int dst_width,
+			    const uint8_t *src, int src_width,
                             int src_start, int src_incr, int16_t *filters)
 {
     int src_pos, phase, sum, j, v, i;
-    uint8_t *s, *src_end;
+    const uint8_t *s, *src_end;
     int16_t *filter;
 
     src_end = src + src_width;
@@ -432,8 +435,9 @@ static void h_resample_slow(uint8_t *dst, int dst_width, uint8_t *src, int src_w
     }
 }
 
-static void h_resample(uint8_t *dst, int dst_width, uint8_t *src, int src_width,
-                       int src_start, int src_incr, int16_t *filters)
+static void h_resample(uint8_t *dst, int dst_width, const uint8_t *src,
+		       int src_width, int src_start, int src_incr,
+		       int16_t *filters)
 {
     int n, src_end;
 
@@ -607,7 +611,7 @@ ImgReSampleContext *img_resample_full_init(int owidth, int oheight,
 }
 
 void img_resample(ImgReSampleContext *s, 
-                  AVPicture *output, AVPicture *input)
+                  AVPicture *output, const AVPicture *input)
 {
     int i, shift;