+ * Since the format of the opened file is in general not known until after
+ * avformat_open_input() has returned, it is not possible to set demuxer private
+ * options on a preallocated context. Instead, the options should be passed to
+ * avformat_open_input() wrapped in an AVDictionary:
+ * @code
+ * AVDictionary *options = NULL;
+ * av_dict_set(&options, "video_size", "640x480", 0);
+ * av_dict_set(&options, "pixel_format", "rgb24", 0);
+ *
+ * if (avformat_open_input(&s, url, NULL, &options) < 0)
+ * abort();
+ * av_dict_free(&options);
+ * @endcode
+ * This code passes the private options 'video_size' and 'pixel_format' to the
+ * demuxer. They would be necessary for e.g. the rawvideo demuxer, since it
+ * cannot know how to interpret raw video data otherwise. If the format turns
+ * out to be something different than raw video, those options will not be
+ * recognized by the demuxer and therefore will not be applied. Such unrecognized
+ * options are then returned in the options dictionary (recognized options are
+ * consumed). The calling program can handle such unrecognized options as it
+ * wishes, e.g.
+ * @code
+ * AVDictionaryEntry *e;
+ * if (e = av_dict_get(options, "", NULL, AV_DICT_IGNORE_SUFFIX)) {
+ * fprintf(stderr, "Option %s not recognized by the demuxer.\n", e->key);
+ * abort();
+ * }
+ * @endcode
+ *