avcodec: add avcodec_enum_to_chroma_pos()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/avcodec.h

@@ -3606,6 +3606,17 @@ void avcodec_align_dimensions(AVCodecContext *s, int *width, int *height);
 void avcodec_align_dimensions2(AVCodecContext *s, int *width, int *height,
                                int linesize_align[AV_NUM_DATA_POINTERS]);
 
+/**
+ * Converts AVChromaLocation to swscale x/y chroma position.
+ *
+ * The positions represent the chroma (0,0) position in a coordinates system
+ * with luma (0,0) representing the origin and luma(1,1) representing 256,256
+ *
+ * @param xpos  horizontal chroma sample position
+ * @param ypos  vertical   chroma sample position
+ */
+int avcodec_enum_to_chroma_pos(int *xpos, int *ypos, enum AVChromaLocation pos);
+
 #if FF_API_OLD_DECODE_AUDIO
 /**
  * Wrapper function which calls avcodec_decode_audio4.

libavcodec/utils.c

@@ -338,6 +338,18 @@ void avcodec_align_dimensions(AVCodecContext *s, int *width, int *height)
     *width              = FFALIGN(*width, align);
 }
 
+int avcodec_enum_to_chroma_pos(int *xpos, int *ypos, enum AVChromaLocation pos)
+{
+    if (pos <= AVCHROMA_LOC_UNSPECIFIED || pos >= AVCHROMA_LOC_NB)
+        return AVERROR(EINVAL);
+    pos--;
+
+    *xpos = (pos&1) * 128;
+    *ypos = ((pos>>1)^(pos<4)) * 128;
+
+    return 0;
+}
+
 int avcodec_fill_audio_frame(AVFrame *frame, int nb_channels,
                              enum AVSampleFormat sample_fmt, const uint8_t *buf,
                              int buf_size, int align)