lavc: add avcodec_is_open().

It allows to check whether an AVCodecContext is open in a documented
way. Right now the undocumented way this check is done in lavf/lavc is
by checking whether AVCodecContext.codec is NULL. However it's desirable
to be able to set AVCodecContext.codec before avcodec_open2().

3 files changed, 15 insertions, 1 deletions

diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index a6bb6863f2..284c7f8cb8 100644
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -4183,4 +4183,10 @@ enum AVMediaType avcodec_get_type(enum CodecID codec_id);
  */
 const AVClass *avcodec_get_class(void);
 
+/**
+ * @return a positive value if s is open (i.e. avcodec_open2() was called on it
+ * with no corresponding avcodec_close()), 0 otherwise.
+ */
+int avcodec_is_open(AVCodecContext *s);
+
 #endif /* AVCODEC_AVCODEC_H */
diff --git a/libavcodec/options.c b/libavcodec/options.c
index c416b4aa4f..52fc66400a 100644
--- a/libavcodec/options.c
+++ b/libavcodec/options.c
@@ -485,7 +485,7 @@ AVCodecContext *avcodec_alloc_context3(AVCodec *codec){
 
 int avcodec_copy_context(AVCodecContext *dest, const AVCodecContext *src)
 {
-    if (dest->codec) { // check that the dest context is uninitialized
+    if (avcodec_is_open(dest)) { // check that the dest context is uninitialized
         av_log(dest, AV_LOG_ERROR,
                "Tried to copy AVCodecContext %p into already-initialized %p\n",
                src, dest);
diff --git a/libavcodec/utils.c b/libavcodec/utils.c
index 34a4122d5d..3ee6b09f74 100644
--- a/libavcodec/utils.c
+++ b/libavcodec/utils.c
@@ -627,6 +627,9 @@ int attribute_align_arg avcodec_open2(AVCodecContext *avctx, AVCodec *codec, AVD
     int ret = 0;
     AVDictionary *tmp = NULL;
 
+    if (avcodec_is_open(avctx))
+        return 0;
+
     if (avctx->extradata_size < 0 || avctx->extradata_size >= FF_MAX_EXTRADATA_SIZE)
         return AVERROR(EINVAL);
 
@@ -1803,3 +1806,8 @@ enum AVMediaType avcodec_get_type(enum CodecID codec_id)
 
     return AVMEDIA_TYPE_UNKNOWN;
 }
+
+int avcodec_is_open(AVCodecContext *s)
+{
+    return !!s->internal;
+}