avformat/utils: Add ff_format_output_open() function

Add ff_format_output_open utility function to wrap
io_open callback of AVFormatContext structure.

Signed-off-by: Jan Sebechlebsky <sebechlebskyjan@gmail.com>
Signed-off-by: Marton Balint <cus@passwd.hu>

libavformat/internal.h

@@ -572,6 +572,16 @@ int ffio_open2_wrapper(struct AVFormatContext *s, AVIOContext **pb, const char *
  */
 #define FFERROR_REDO FFERRTAG('R','E','D','O')
 
+/**
+ * Utility function to open IO stream of output format.
+ *
+ * @param s AVFormatContext
+ * @param url URL or file name to open for writing
+ * @options optional options which will be passed to io_open callback
+ * @return >=0 on success, negative AVERROR in case of failure
+ */
+int ff_format_output_open(AVFormatContext *s, const char *url, AVDictionary **options);
+
 /*
  * A wrapper around AVFormatContext.io_close that should be used
  * instead of calling the pointer directly.

libavformat/utils.c

@@ -5169,6 +5169,16 @@ int av_apply_bitstream_filters(AVCodecContext *codec, AVPacket *pkt,
 FF_ENABLE_DEPRECATION_WARNINGS
 #endif
 
+int ff_format_output_open(AVFormatContext *s, const char *url, AVDictionary **options)
+{
+    if (!s->oformat)
+        return AVERROR(EINVAL);
+
+    if (!(s->oformat->flags & AVFMT_NOFILE))
+        return s->io_open(s, &s->pb, url, AVIO_FLAG_WRITE, options);
+    return 0;
+}
+
 void ff_format_io_close(AVFormatContext *s, AVIOContext **pb)
 {
     if (*pb)