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lavf doxy: document passing options to demuxers.

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Anton Khirnov 2012-01-03 08:34:55 +01:00
parent dca9c81d82
commit 10fa4ff7bc
1 changed files with 41 additions and 0 deletions
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libavformat/avformat.h
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@ -66,6 +66,18 @@
* set by user for input, always set by user for output (unless you are dealing
* with an AVFMT_NOFILE format).
*
* @section lavf_options Passing options to (de)muxers
* Lavf allows to configure muxers and demuxers using the @ref avoptions
* mechanism. Generic (format-independent) libavformat options are provided by
* AVFormatContext, they can be examined from a user program by calling
* av_opt_next() / av_opt_find() on an allocated AVFormatContext (or its AVClass
* from avformat_get_class()). Private (format-specific) options are provided by
* AVFormatContext.priv_data if and only if AVInputFormat.priv_class /
* AVOutputFormat.priv_class of the corresponding format struct is non-NULL.
* Further options may be provided by the @ref AVFormatContext.pb "I/O context",
* if its AVClass is non-NULL, and the protocols layer. See the discussion on
* nesting in @ref avoptions documentation to learn how to access those.
*
* @defgroup lavf_decoding Demuxing
* @{
* Demuxers read a media file and split it into chunks of data (@em packets). A
@ -100,6 +112,35 @@
* your reading callbacks to it. Then set the @em pb field of your
* AVFormatContext to newly created AVIOContext.
*
* 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
*
* After you have finished reading the file, you must close it with
* avformat_close_input(). It will free everything associated with the file.
*