Converting Ogg’s COVERART tag

[Sebastian Dröge]

On Mo, 2013-12-16 at 04:46 +0100, Marcus Habermehl wrote:
> Sorry, for the late answer. I was very busy the last week.
> 
> Am 07.12.2013 11:31, schrieb Sebastian Dröge:
> > On Fr, 2013-12-06 at 15:37 +0100, Marcus Habermehl wrote:
> >> Hi.
> >>
> >> I have some Ogg files with the deprecated COVERART tag that I would like
> >> to convert to the METADATA_BLOCK_PICTURE tag.
> >>
> >> For this I have written a small Python script to automatically do this
> >> with GStreamer.
> >>
> >> How I can read tags, modify and write back I have already found out.
> >>
> >> Unfortunately, the GST_TAG_IMAGE is not written as I expected. But I do
> >> not know if this is due to my code, or due to the GIR bindings.
> >>
> >> I get the original tags from the bus with a first pipeline (urisrc !
> >> oggdemux ! oggmux ! fakesink). With these tags I create a modified
> >> GstTagList.
> >>
> >> The COVERART tag is here changed from GST_TAG_PREVIEW_IMAGE to
> >> GST_TAG_IMAGE and for the value I create a new GstSample. (‘value’ is
> >> the value of the original tag.)
> >>
> >> buffer = value.get_buffer()
> >> mime_struct = value.get_caps().get_structure(0)
> >> mime_type = mime_struct.get_name()
> >>
> >> structure = Gst.Structure.new_empty(mime_type)
> >> structure.set_value("height", mime_struct.get_value("height"))
> >> structure.set_value("image-type", GstTag.TagImageType.FRONT_COVER)
> >> structure.set_value("width", mime_struct.get_value("width"))
> >>
> >> caps = Gst.Caps.new_empty()
> >> caps.append_structure(structure)
> >>
> >> sample = Gst.Sample.new(value.get_buffer(), caps, value.get_segment(), None)
> >>
> >> The modified GstTagList is written with a second pipeline (urisrc
> >> oggdemux ! vorbistag ! oggmux ! urisink) correctly. But in GST_TAG_IMAGE
> >> the ‘image-type’ field is removed from the GstSample. At least it is
> >> when I reading the written tags no longer present.
> > 
> > The code is writing the image type, or at least tries to. Does it show
> > up in other software that does not use GStreamer? Can you provide a file
> > that was created this way?
> 
> I have installed an application that doesn’t use GStreamer and it shows
> the image type as expected.
> 
> Here is an Ogg file that I have created this way:
> http://ubuntuone.com/6LfawrpRf20KQHO4ZeGZTd

It correctly includes the image type in the GstSample here, it's a
GST_TAG_IMAGE_TYPE_FRONT_COVER. How do you get the image type from the
sample? The image type is supposed to be in the structure that you can
get with gst_sample_get_info().

There's a bug here in gstvorbistag.c, where it takes the image-info from
the caps when you *create* the tag but puts it into the info structure
when it *reads* the tag from the file. Fixing that now.

> >> I also found no hint in the documentation, how can I set a description
> >> for the image.
> > 
> > Setting a description is currently not supported, could you file a
> > feature request bug about that at http://bugzilla.gnome.org against
> > GStreamer? Should be easy to add in
> > gst-plugins-base/gst-libs/gst/tag/gstvorbistag.c
> 
> Does this affect vorbistag, only? Or is it generally not supported?

Yes, only vorbistag.

-- 
Sebastian Dröge, Centricular Ltd - http://www.centricular.com
Expertise, Straight from the Source
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