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<div id="projectname">FFmpeg
 <span id="projectnumber">2.7.1</span>
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<div class="title">Public Metadata API</div> </div>
<div class="ingroups"><a class="el" href="group__libavf.html">I/O and Muxing/Demuxing Library</a></div></div><!--header-->
<div class="contents">
<p>The metadata API allows libavformat to export metadata tags to a client application when demuxing.
<a href="#details">More...</a></p>
<p>The metadata API allows libavformat to export metadata tags to a client application when demuxing. </p>
<p>Conversely it allows a client application to set metadata when muxing.</p>
<p>Metadata is exported or set as pairs of key/value strings in the 'metadata' fields of the <a class="el" href="structAVFormatContext.html" title="Format I/O context.">AVFormatContext</a>, <a class="el" href="structAVStream.html" title="Stream structure.">AVStream</a>, <a class="el" href="structAVChapter.html">AVChapter</a> and <a class="el" href="structAVProgram.html" title="New fields can be added to the end with minor version bumps.">AVProgram</a> structs using the <a class="el" href="group__lavu__dict.html">AVDictionary</a> API. Like all strings in FFmpeg, metadata is assumed to be UTF-8 encoded Unicode. Note that metadata exported by demuxers isn't checked to be valid UTF-8 in most cases.</p>
<p>Important concepts to keep in mind:</p>
<ul>
<li>Keys are unique; there can never be 2 tags with the same key. This is also meant semantically, i.e., a demuxer should not knowingly produce several keys that are literally different but semantically identical. E.g., key=Author5, key=Author6. In this example, all authors must be placed in the same tag.</li>
<li>Metadata is flat, not hierarchical; there are no subtags. If you want to store, e.g., the email address of the child of producer Alice and actor Bob, that could have key=alice_and_bobs_childs_email_address.</li>
<li>Several modifiers can be applied to the tag name. This is done by appending a dash character ('-') and the modifier name in the order they appear in the list below -- e.g. foo-eng-sort, not foo-sort-eng.<ul>
<li>language -- a tag whose value is localized for a particular language is appended with the ISO 639-2/B 3-letter language code. For example: Author-ger=Michael, Author-eng=Mike The original/default language is in the unqualified "Author" tag. A demuxer should set a default if it sets any translated tag.</li>
<li>sorting -- a modified version of a tag that should be used for sorting will have '-sort' appended. E.g. artist="The Beatles", artist-sort="Beatles, The".</li>
</ul>
</li>
<li>Some protocols and demuxers support metadata updates. After a successful call to av_read_packet(), <a class="el" href="structAVFormatContext.html#a0302506d4b3434da77b8b3db43821aa0" title="Flags for the user to detect events happening on the file.">AVFormatContext.event_flags</a> or <a class="el" href="structAVStream.html#ab76e176c2a1d1ff09ec9c0bb88dc25e9" title="Flags for the user to detect events happening on the stream.">AVStream.event_flags</a> will be updated to indicate if metadata changed. In order to detect metadata changes on a stream, you need to loop through all streams in the <a class="el" href="structAVFormatContext.html" title="Format I/O context.">AVFormatContext</a> and check their individual event_flags.</li>
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<ul>
<li>Demuxers attempt to export metadata in a generic format, however tags with no generic equivalents are left as they are stored in the container. Follows a list of generic tag names:</li>
</ul>
<div class="fragment"><pre class="fragment">
album -- name of the set this work belongs to
album_artist -- main creator of the set/album, if different from artist.
e.g. "Various Artists" for compilation albums.
artist -- main creator of the work
comment -- any additional description of the file.
composer -- who composed the work, if different from artist.
copyright -- name of copyright holder.
creation_time-- date when the file was created, preferably in ISO 8601.
date -- date when the work was created, preferably in ISO 8601.
disc -- number of a subset, e.g. disc in a multi-disc collection.
encoder -- name/settings of the software/hardware that produced the file.
encoded_by -- person/group who created the file.
filename -- original name of the file.
genre -- <self-evident>.
language -- main language in which the work is performed, preferably
in ISO 639-2 format. Multiple languages can be specified by
separating them with commas.
performer -- artist who performed the work, if different from artist.
E.g for "Also sprach Zarathustra", artist would be "Richard
Strauss" and performer "London Philharmonic Orchestra".
publisher -- name of the label/publisher.
service_name -- name of the service in broadcasting (channel name).
service_provider -- name of the service provider in broadcasting.
title -- name of the work.
track -- number of this work in the set, can be in form current/total.
variant_bitrate -- the total bitrate of the bitrate variant that the current stream is part of
</pre></div><p>Look in the examples section for an application example how to use the Metadata API. </p>
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