lavd/avdevice: introduce helper functions for sink/sources listing

Signed-off-by: Lukasz Marek <lukasz.m.luki2@gmail.com>

libavdevice/utils.c

@@ -0,0 +1,59 @@
+/*
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "internal.h"
+#include "libavutil/opt.h"
+#include "libavformat/avformat.h"
+
+int ff_alloc_input_device_context(AVFormatContext **avctx, AVInputFormat *iformat, const char *format)
+{
+    AVFormatContext *s;
+    int ret = 0;
+
+    *avctx = NULL;
+    if (!iformat && !format)
+        return AVERROR(EINVAL);
+    if (!(s = avformat_alloc_context()))
+        return AVERROR(ENOMEM);
+
+    if (!iformat)
+        iformat = av_find_input_format(format);
+    if (!iformat || !iformat->priv_class || !AV_IS_INPUT_DEVICE(iformat->priv_class->category)) {
+        ret = AVERROR(EINVAL);
+        goto error;
+    }
+    s->iformat = iformat;
+    if (s->iformat->priv_data_size > 0) {
+        s->priv_data = av_mallocz(s->iformat->priv_data_size);
+        if (!s->priv_data) {
+            ret = AVERROR(ENOMEM);
+            goto error;
+        }
+        if (s->iformat->priv_class) {
+            *(const AVClass**)s->priv_data= s->iformat->priv_class;
+            av_opt_set_defaults(s->priv_data);
+        }
+    } else
+        s->priv_data = NULL;
+
+    *avctx = s;
+    return 0;
+  error:
+    avformat_free_context(s);
+    return ret;
+}