diff --git a/doc/APIchanges b/doc/APIchanges
index fb5534b5f5..9de23744c0 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -15,6 +15,10 @@ libavutil:     2017-10-21
 
 API changes, most recent first:
 
+2020-06-xx - xxxxxxxxxx
+  Change AVBufferRef related function and struct size parameter and fields
+  type to size_t at next major bump.
+
 2020-xx-xx - xxxxxxxxxx - lavc 58.88.100 - avcodec.h codec.h
   Move AVCodec-related public API to new header codec.h.
 
diff --git a/libavutil/buffer.c b/libavutil/buffer.c
index 6d9cb7428e..0a29430381 100644
--- a/libavutil/buffer.c
+++ b/libavutil/buffer.c
@@ -26,7 +26,11 @@
 #include "mem.h"
 #include "thread.h"
 
+#if FF_API_BUFFER_SIZE_T
 AVBufferRef *av_buffer_create(uint8_t *data, int size,
+#else
+AVBufferRef *av_buffer_create(uint8_t *data, size_t size,
+#endif
                               void (*free)(void *opaque, uint8_t *data),
                               void *opaque, int flags)
 {
@@ -65,7 +69,11 @@ void av_buffer_default_free(void *opaque, uint8_t *data)
     av_free(data);
 }
 
+#if FF_API_BUFFER_SIZE_T
 AVBufferRef *av_buffer_alloc(int size)
+#else
+AVBufferRef *av_buffer_alloc(size_t size)
+#endif
 {
     AVBufferRef *ret = NULL;
     uint8_t    *data = NULL;
@@ -81,7 +89,11 @@ AVBufferRef *av_buffer_alloc(int size)
     return ret;
 }
 
+#if FF_API_BUFFER_SIZE_T
 AVBufferRef *av_buffer_allocz(int size)
+#else
+AVBufferRef *av_buffer_allocz(size_t size)
+#endif
 {
     AVBufferRef *ret = av_buffer_alloc(size);
     if (!ret)
@@ -167,7 +179,11 @@ int av_buffer_make_writable(AVBufferRef **pbuf)
     return 0;
 }
 
+#if FF_API_BUFFER_SIZE_T
 int av_buffer_realloc(AVBufferRef **pbuf, int size)
+#else
+int av_buffer_realloc(AVBufferRef **pbuf, size_t size)
+#endif
 {
     AVBufferRef *buf = *pbuf;
     uint8_t *tmp;
@@ -216,8 +232,13 @@ int av_buffer_realloc(AVBufferRef **pbuf, int size)
     return 0;
 }
 
+#if FF_API_BUFFER_SIZE_T
 AVBufferPool *av_buffer_pool_init2(int size, void *opaque,
                                    AVBufferRef* (*alloc)(void *opaque, int size),
+#else
+AVBufferPool *av_buffer_pool_init2(size_t size, void *opaque,
+                                   AVBufferRef* (*alloc)(void *opaque, size_t size),
+#endif
                                    void (*pool_free)(void *opaque))
 {
     AVBufferPool *pool = av_mallocz(sizeof(*pool));
@@ -236,7 +257,11 @@ AVBufferPool *av_buffer_pool_init2(int size, void *opaque,
     return pool;
 }
 
+#if FF_API_BUFFER_SIZE_T
 AVBufferPool *av_buffer_pool_init(int size, AVBufferRef* (*alloc)(int size))
+#else
+AVBufferPool *av_buffer_pool_init(size_t size, AVBufferRef* (*alloc)(size_t size))
+#endif
 {
     AVBufferPool *pool = av_mallocz(sizeof(*pool));
     if (!pool)
diff --git a/libavutil/buffer.h b/libavutil/buffer.h
index e0f94314f4..547c376439 100644
--- a/libavutil/buffer.h
+++ b/libavutil/buffer.h
@@ -27,6 +27,8 @@
 
 #include <stdint.h>
 
+#include "version.h"
+
 /**
  * @defgroup lavu_buffer AVBuffer
  * @ingroup lavu_data
@@ -90,7 +92,11 @@ typedef struct AVBufferRef {
     /**
      * Size of data in bytes.
      */
+#if FF_API_BUFFER_SIZE_T
     int      size;
+#else
+    size_t   size;
+#endif
 } AVBufferRef;
 
 /**
@@ -98,13 +104,21 @@ typedef struct AVBufferRef {
  *
  * @return an AVBufferRef of given size or NULL when out of memory
  */
+#if FF_API_BUFFER_SIZE_T
 AVBufferRef *av_buffer_alloc(int size);
+#else
+AVBufferRef *av_buffer_alloc(size_t size);
+#endif
 
 /**
  * Same as av_buffer_alloc(), except the returned buffer will be initialized
  * to zero.
  */
+#if FF_API_BUFFER_SIZE_T
 AVBufferRef *av_buffer_allocz(int size);
+#else
+AVBufferRef *av_buffer_alloc(size_t size);
+#endif
 
 /**
  * Always treat the buffer as read-only, even when it has only one
@@ -127,7 +141,11 @@ AVBufferRef *av_buffer_allocz(int size);
  *
  * @return an AVBufferRef referring to data on success, NULL on failure.
  */
+#if FF_API_BUFFER_SIZE_T
 AVBufferRef *av_buffer_create(uint8_t *data, int size,
+#else
+AVBufferRef *av_buffer_create(uint8_t *data, size_t size,
+#endif
                               void (*free)(void *opaque, uint8_t *data),
                               void *opaque, int flags);
 
@@ -195,7 +213,11 @@ int av_buffer_make_writable(AVBufferRef **buf);
  * reference to it (i.e. the one passed to this function). In all other cases
  * a new buffer is allocated and the data is copied.
  */
+#if FF_API_BUFFER_SIZE_T
 int av_buffer_realloc(AVBufferRef **buf, int size);
+#else
+int av_buffer_realloc(AVBufferRef **buf, size_t size);
+#endif
 
 /**
  * @}
@@ -246,7 +268,11 @@ typedef struct AVBufferPool AVBufferPool;
  * (av_buffer_alloc()).
  * @return newly created buffer pool on success, NULL on error.
  */
+#if FF_API_BUFFER_SIZE_T
 AVBufferPool *av_buffer_pool_init(int size, AVBufferRef* (*alloc)(int size));
+#else
+AVBufferPool *av_buffer_pool_init(size_t size, AVBufferRef* (*alloc)(size_t size));
+#endif
 
 /**
  * Allocate and initialize a buffer pool with a more complex allocator.
@@ -262,8 +288,13 @@ AVBufferPool *av_buffer_pool_init(int size, AVBufferRef* (*alloc)(int size));
  *                  data.
  * @return newly created buffer pool on success, NULL on error.
  */
+#if FF_API_BUFFER_SIZE_T
 AVBufferPool *av_buffer_pool_init2(int size, void *opaque,
                                    AVBufferRef* (*alloc)(void *opaque, int size),
+#else
+AVBufferPool *av_buffer_pool_init2(size_t size, void *opaque,
+                                   AVBufferRef* (*alloc)(void *opaque, size_t size),
+#endif
                                    void (*pool_free)(void *opaque));
 
 /**
diff --git a/libavutil/buffer_internal.h b/libavutil/buffer_internal.h
index 54b67047e5..c2f9342422 100644
--- a/libavutil/buffer_internal.h
+++ b/libavutil/buffer_internal.h
@@ -36,7 +36,11 @@
 
 struct AVBuffer {
     uint8_t *data; /**< data described by this buffer */
+#if FF_API_BUFFER_SIZE_T
     int      size; /**< size of data in bytes */
+#else
+    size_t   size; /**< size of data in bytes */
+#endif
 
     /**
      *  number of existing AVBufferRef instances referring to this buffer
@@ -88,10 +92,19 @@ struct AVBufferPool {
      */
     atomic_uint refcount;
 
+#if FF_API_BUFFER_SIZE_T
     int size;
+#else
+    size_t size;
+#endif
     void *opaque;
+#if FF_API_BUFFER_SIZE_T
     AVBufferRef* (*alloc)(int size);
     AVBufferRef* (*alloc2)(void *opaque, int size);
+#else
+    AVBufferRef* (*alloc)(size_t size);
+    AVBufferRef* (*alloc2)(void *opaque, size_t size);
+#endif
     void         (*pool_free)(void *opaque);
 };
 
diff --git a/libavutil/version.h b/libavutil/version.h
index 7acecf5a97..431eb1d571 100644
--- a/libavutil/version.h
+++ b/libavutil/version.h
@@ -129,6 +129,9 @@
 #ifndef FF_API_PSEUDOPAL
 #define FF_API_PSEUDOPAL                (LIBAVUTIL_VERSION_MAJOR < 57)
 #endif
+#ifndef FF_API_BUFFER_SIZE_T
+#define FF_API_BUFFER_SIZE_T            (LIBAVUTIL_VERSION_MAJOR < 57)
+#endif
 
 
 /**
