lavc, lavu: move frame cropping to a convenience function

Signed-off-by: Anton Khirnov <anton@khirnov.net>

Merged from Libav commit 47399ccdfd.

libavutil/frame.h

@@ -773,6 +773,40 @@ AVFrameSideData *av_frame_get_side_data(const AVFrame *frame,
  */
 void av_frame_remove_side_data(AVFrame *frame, enum AVFrameSideDataType type);
 
+
+/**
+ * Flags for frame cropping.
+ */
+enum {
+    /**
+     * Apply the maximum possible cropping, even if it requires setting the
+     * AVFrame.data[] entries to unaligned pointers. Passing unaligned data
+     * to Libav API is generally not allowed, and causes undefined behavior
+     * (such as crashes). You can pass unaligned data only to Libav APIs that
+     * are explicitly documented to accept it. Use this flag only if you
+     * absolutely know what you are doing.
+     */
+    AV_FRAME_CROP_UNALIGNED     = 1 << 0,
+};
+
+/**
+ * Crop the given video AVFrame according to its crop_left/crop_top/crop_right/
+ * crop_bottom fields. If cropping is successful, the function will adjust the
+ * data pointers and the width/height fields, and set the crop fields to 0.
+ *
+ * In all cases, the cropping boundaries will be rounded to the inherent
+ * alignment of the pixel format. In some cases, such as for opaque hwaccel
+ * formats, the left/top cropping is ignored. The crop fields are set to 0 even
+ * if the cropping was rounded or ignored.
+ *
+ * @param frame the frame which should be cropped
+ * @param flags Some combination of AV_FRAME_CROP_* flags, or 0.
+ *
+ * @return >= 0 on success, a negative AVERROR on error. If the cropping fields
+ * were invalid, AVERROR(ERANGE) is returned, and nothing is changed.
+ */
+int av_frame_apply_cropping(AVFrame *frame, int flags);
+
 /**
  * @return a string identifying the side data type
  */