hwcontext: add a function for opening devices

doc/APIchanges

@@ -13,6 +13,9 @@ libavutil:     2015-08-28
 
 API changes, most recent first:
 
+2016-xx-xx - xxxxxxx - lavu 55.13.0 - hwcontext.h
+  Add av_hwdevice_ctx_create().
+
 2016-xx-xx - xxxxxxx - lavc 57.19.1 - avcodec.h
   Adjust values for JPEG 2000 profiles.
 

libavutil/hwcontext.c

@@ -452,3 +452,39 @@ void av_hwframe_constraints_free(AVHWFramesConstraints **constraints)
     }
     av_freep(constraints);
 }
+
+int av_hwdevice_ctx_create(AVBufferRef **pdevice_ref, enum AVHWDeviceType type,
+                           const char *device, AVDictionary *opts, int flags)
+{
+    AVBufferRef *device_ref = NULL;
+    AVHWDeviceContext *device_ctx;
+    int ret = 0;
+
+    device_ref = av_hwdevice_ctx_alloc(type);
+    if (!device_ref) {
+        ret = AVERROR(ENOMEM);
+        goto fail;
+    }
+    device_ctx = (AVHWDeviceContext*)device_ref->data;
+
+    if (!device_ctx->internal->hw_type->device_create) {
+        ret = AVERROR(ENOSYS);
+        goto fail;
+    }
+
+    ret = device_ctx->internal->hw_type->device_create(device_ctx, device,
+                                                       opts, flags);
+    if (ret < 0)
+        goto fail;
+
+    ret = av_hwdevice_ctx_init(device_ref);
+    if (ret < 0)
+        goto fail;
+
+    *pdevice_ref = device_ref;
+    return 0;
+fail:
+    av_buffer_unref(&device_ref);
+    *pdevice_ref = NULL;
+    return ret;
+}

libavutil/hwcontext.h

@@ -241,6 +241,34 @@ AVBufferRef *av_hwdevice_ctx_alloc(enum AVHWDeviceType type);
  */
 int av_hwdevice_ctx_init(AVBufferRef *ref);
 
+/**
+ * Open a device of the specified type and create an AVHWDeviceContext for it.
+ *
+ * This is a convenience function intended to cover the simple cases. Callers
+ * who need to fine-tune device creation/management should open the device
+ * manually and then wrap it in an AVHWDeviceContext using
+ * av_hwdevice_ctx_alloc()/av_hwdevice_ctx_init().
+ *
+ * The returned context is already initialized and ready for use, the caller
+ * should not call av_hwdevice_ctx_init() on it. The user_opaque/free fields of
+ * the created AVHWDeviceContext are set by this function and should not be
+ * touched by the caller.
+ *
+ * @param device_ctx On success, a reference to the newly-created device context
+ *                   will be written here. The reference is owned by the caller
+ *                   and must be released with av_buffer_unref() when no longer
+ *                   needed. On failure, NULL will be written to this pointer.
+ * @param type The type of the device to create.
+ * @param device A type-specific string identifying the device to open.
+ * @param opts A dictionary of additional (type-specific) options to use in
+ *             opening the device. The dictionary remains owned by the caller.
+ * @param flags currently unused
+ *
+ * @return 0 on success, a negative AVERROR code on failure.
+ */
+int av_hwdevice_ctx_create(AVBufferRef **device_ctx, enum AVHWDeviceType type,
+                           const char *device, AVDictionary *opts, int flags);
+
 /**
  * Allocate an AVHWFramesContext tied to a given device context.
  *

libavutil/hwcontext_internal.h

@@ -64,6 +64,9 @@ typedef struct HWContextType {
      */
     size_t             frames_priv_size;
 
+    int              (*device_create)(AVHWDeviceContext *ctx, const char *device,
+                                      AVDictionary *opts, int flags);
+
     int              (*device_init)(AVHWDeviceContext *ctx);
     void             (*device_uninit)(AVHWDeviceContext *ctx);
 

libavutil/version.h

@@ -54,7 +54,7 @@
  */
 
 #define LIBAVUTIL_VERSION_MAJOR 55
-#define LIBAVUTIL_VERSION_MINOR 12
+#define LIBAVUTIL_VERSION_MINOR 13
 #define LIBAVUTIL_VERSION_MICRO  0
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \