lavc: Add device context field to AVCodecContext

For use by codec implementations which can allocate frames internally.

doc/APIchanges

@@ -13,6 +13,9 @@ libavutil:     2015-08-28
 
 API changes, most recent first:
 
+2017-xx-xx - xxxxxxx - lavc 57.34.0 - avcodec.h
+  Add AVCodecContext.hw_device_ctx.
+
 2017-02-11 - xxxxxxx - lavu 55.32.0 - frame.h
   Add AVFrame.opaque_ref.
 

libavcodec/avcodec.h

@@ -3093,7 +3093,8 @@ typedef struct AVCodecContext {
     /**
      * A reference to the AVHWFramesContext describing the input (for encoding)
      * or output (decoding) frames. The reference is set by the caller and
-     * afterwards owned (and freed) by libavcodec.
+     * afterwards owned (and freed) by libavcodec - it should never be read by
+     * the caller after being set.
      *
      * - decoding: This field should be set by the caller from the get_format()
      *             callback. The previous reference (if any) will always be
@@ -3139,6 +3140,28 @@ typedef struct AVCodecContext {
      * (with the display dimensions being determined by the crop_* fields).
      */
     int apply_cropping;
+
+    /**
+     * A reference to the AVHWDeviceContext describing the device which will
+     * be used by a hardware encoder/decoder.  The reference is set by the
+     * caller and afterwards owned (and freed) by libavcodec.
+     *
+     * This should be used if either the codec device does not require
+     * hardware frames or any that are used are to be allocated internally by
+     * libavcodec.  If the user wishes to supply any of the frames used as
+     * encoder input or decoder output then hw_frames_ctx should be used
+     * instead.  When hw_frames_ctx is set in get_format() for a decoder, this
+     * field will be ignored while decoding the associated stream segment, but
+     * may again be used on a following one after another get_format() call.
+     *
+     * For both encoders and decoders this field should be set before
+     * avcodec_open2() is called and must not be written to thereafter.
+     *
+     * Note that some decoders may require this field to be set initially in
+     * order to support hw_frames_ctx at all - in that case, all frames
+     * contexts used must be created on the same device.
+     */
+    AVBufferRef *hw_device_ctx;
 } AVCodecContext;
 
 /**

libavcodec/utils.c

@@ -794,6 +794,7 @@ av_cold int avcodec_close(AVCodecContext *avctx)
     avctx->nb_coded_side_data = 0;
 
     av_buffer_unref(&avctx->hw_frames_ctx);
+    av_buffer_unref(&avctx->hw_device_ctx);
 
     if (avctx->priv_data && avctx->codec && avctx->codec->priv_class)
         av_opt_free(avctx->priv_data);

libavcodec/version.h

@@ -28,7 +28,7 @@
 #include "libavutil/version.h"
 
 #define LIBAVCODEC_VERSION_MAJOR 57
-#define LIBAVCODEC_VERSION_MINOR 33
+#define LIBAVCODEC_VERSION_MINOR 34
 #define LIBAVCODEC_VERSION_MICRO  0
 
 #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \