[FFmpeg-devel] [PATCH] avutil/frame: add new functions to get frame side data

[Leandro Santiago <leandrosansilva@gmail.com>]

The functions are:

av_frame_side_data_get_nth_c()
av_frame_side_data_get_nth()
av_frame_get_nth_side_data()

They mimic the counterparts without the `_nth` suffix/infix, with an extra
argument, which specifies the relative position of the entry of a given
type.

Signed-off-by: Leandro Santiago <leandrosansilva@gmail.com>
---
 libavutil/frame.c     | 10 ++++++++++
 libavutil/frame.h     | 43 ++++++++++++++++++++++++++++++++++++++++---
 libavutil/side_data.c | 14 +++++++++++---
 3 files changed, 61 insertions(+), 6 deletions(-)

diff --git a/libavutil/frame.c b/libavutil/frame.c
index 71bde48f8b..dd0fd06378 100644
--- a/libavutil/frame.c
+++ b/libavutil/frame.c
@@ -699,6 +699,16 @@ AVFrameSideData *av_frame_get_side_data(const AVFrame *frame,
     );
 }
 
+AVFrameSideData *av_frame_get_nth_side_data(const AVFrame *frame,
+                                            enum AVFrameSideDataType type,
+                                            int n)
+{
+    return (AVFrameSideData *)av_frame_side_data_get_nth(
+        frame->side_data, frame->nb_side_data,
+        type, n
+    );
+}
+
 static int frame_copy_video(AVFrame *dst, const AVFrame *src)
 {
     int planes;
diff --git a/libavutil/frame.h b/libavutil/frame.h
index 49260ae2dd..56375280bb 100644
--- a/libavutil/frame.h
+++ b/libavutil/frame.h
@@ -1017,12 +1017,22 @@ AVFrameSideData *av_frame_new_side_data_from_buf(AVFrame *frame,
                                                  AVBufferRef *buf);
 
 /**
- * @return a pointer to the side data of a given type on success, NULL if there
+ * @return a pointer to the first side data of a given type on success, NULL if there
  * is no side data with such type in this frame.
  */
 AVFrameSideData *av_frame_get_side_data(const AVFrame *frame,
                                         enum AVFrameSideDataType type);
 
+/**
+ * @return a pointer to the side data of a given type on success,
+ * after skipping the first matches. Otherwise return NULL if there
+ * is no side data with such type in this frame or if all the matches were skipped.
+ * @param n the relative position of the side data entry
+ */
+AVFrameSideData *av_frame_get_nth_side_data(const AVFrame *frame,
+                                            enum AVFrameSideDataType type,
+                                            int n);
+
 /**
  * Remove and free all side data instances of the given type.
  */
@@ -1170,7 +1180,7 @@ int av_frame_side_data_clone(AVFrameSideData ***sd, int *nb_sd,
                              const AVFrameSideData *src, unsigned int flags);
 
 /**
- * Get a side data entry of a specific type from an array.
+ * Get the first side data entry of a specific type from an array.
  *
  * @param sd    array of side data.
  * @param nb_sd integer containing the number of entries in the array.
@@ -1184,7 +1194,24 @@ const AVFrameSideData *av_frame_side_data_get_c(const AVFrameSideData * const *s
                                                 enum AVFrameSideDataType type);
 
 /**
- * Wrapper around av_frame_side_data_get_c() to workaround the limitation
+ * Get a side data entry of a specific type from an array.
+ *
+ * @param sd    array of side data.
+ * @param nb_sd integer containing the number of entries in the array.
+ * @param type  type of side data to be queried
+ * @param n     relative position of the side data entry.
+ *
+ * @return a pointer to the side data of a given type on success, NULL if there
+ *         is no side data with such type in this set or all the entries were skipped.
+ */
+const AVFrameSideData *av_frame_side_data_get_nth_c(const AVFrameSideData * const *sd,
+                                                    const int nb_sd,
+                                                    enum AVFrameSideDataType type,
+                                                    int n
+);
+
+/**
+ * Wrappers around av_frame_side_data_get{_nth}_c() and to workaround the limitation
  * that for any type T the conversion from T * const * to const T * const *
  * is not performed automatically in C.
  * @see av_frame_side_data_get_c()
@@ -1198,6 +1225,16 @@ const AVFrameSideData *av_frame_side_data_get(AVFrameSideData * const *sd,
                                     nb_sd, type);
 }
 
+static inline
+const AVFrameSideData *av_frame_side_data_get_nth(AVFrameSideData * const *sd,
+                                                  const int nb_sd,
+                                                  enum AVFrameSideDataType type,
+                                                  int n)
+{
+    return av_frame_side_data_get_nth_c((const AVFrameSideData * const *)sd,
+                                        nb_sd, type, n);
+}
+
 /**
  * Remove and free all side data instances of the given type from an array.
  */
diff --git a/libavutil/side_data.c b/libavutil/side_data.c
index 17965f2d3c..bfe408e611 100644
--- a/libavutil/side_data.c
+++ b/libavutil/side_data.c
@@ -301,13 +301,21 @@ int av_frame_side_data_clone(AVFrameSideData ***sd, int *nb_sd,
     return 0;
 }
 
-const AVFrameSideData *av_frame_side_data_get_c(const AVFrameSideData * const *sd,
+const AVFrameSideData *av_frame_side_data_get_nth_c(const AVFrameSideData * const *sd,
                                                 const int nb_sd,
-                                                enum AVFrameSideDataType type)
+                                                enum AVFrameSideDataType type,
+                                                int n)
 {
     for (int i = 0; i < nb_sd; i++) {
-        if (sd[i]->type == type)
+        if (sd[i]->type == type && --n < 0)
             return sd[i];
     }
     return NULL;
 }
+
+const AVFrameSideData *av_frame_side_data_get_c(const AVFrameSideData * const *sd,
+                                                const int nb_sd,
+                                                enum AVFrameSideDataType type)
+{
+    return av_frame_side_data_get_nth_c(sd, nb_sd, type, 0);
+}
-- 
2.48.1

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