[gstreamer-bugs] [Bug 486659] metadata parser for image files

[GStreamer (bugzilla.gnome.org)]

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  GStreamer | gst-plugins-bad | Ver: HEAD CVS




------- Comment #6 from Stefan Kost (gstreamer, gtkdoc dev)  2007-10-15 14:13 UTC -------
EXIF, XMP, IPCT are different from id3 or vorbiscomments. The standarts for
metadata we are talking here about describes how to format it and how to embed
this in various formats. In most cases it will be stored inside the container
(and that the level of support we would like to address).

Now basically all format in which we would like to support it would need to
parse the chunk and emit tags when reading and format the tags into a chunk
when writing. How the chunk is streamlined with the container-format is
specific, but the content of the chunk is not.

So basically when reading the app will do:
tags = gst_tag_list_from_exif_chunk (buffer)
when it found an exif chunk. If the proposed utility library has exif support
gst_tag_list_from_exif_chunk will parse the block and generate single tags, if
not it could emit GST_TAG_EXIF with the exif binary blob.

When writing the app will do:
buffer = gst_exif_chunk_from_tag_list (tags)
if there is exif support in the lib it will check if there are suitable tags
are in the taglist it will return a buffer, else NULL. if there is no exif
support it will check if there is GST_TAG_EXIF and return that.

This way we don't clutter several elements with #ifdef HAVE_LIBEXIF and we
preserve the metadata for e.g. filesrc ! pngdec ! jpegenc ! filesink. If the
libs are available one can even change the metadata.


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