Possible inconsistencies between python and C API

[Antonio Ospite]

Hi,

I wanted to brush up my GStreamer game and I though I'd write some
example elements in python to fixate some concepts without the
distracting C boilerplate.

In particular I was writing a demuxer and a parser and I noticed what
I think may be inconsistencies between the C API and the python
bindings:

1. GstBase.Adapter.map() and GstBase.Adapter.take() do not take
   a size/nbytes argument in the python bindings[1,2] as they do in the
   C API[3,4]. This was confusing at first but it is not a great
   shortcoming as the GstBase.Adapter.take_*() functions seem to work
   fine and can be used instead.

2. GstBase.BaseParse.do_handle_frame() has the "skipsize (int)"
   parameter which is an input-only parameter in python[5], while in
   C it is an output parameter[6], so it looks like it's not possible to
   pass a "skipsize" value to the caller to skip some data.  I would
   have expected to pass "skipsize" in the return value of the python
   function.
   
   This affects the generality of BaseParse in python, in my parser
   element I have to skip some header and only pass the payload
   downstream, and I didn't find an alternative way to do it in python
   with BaseParse.

   There could be a similar problem with the "dest_value" parameter of
   GstBase.BaseParse.do_convert() but I don't use that function.

3. To overcome 2. I tried, just as an experiment, to skip some data in
   the parser element with frame.buffer.remove_memory_range(0, skipsize)
   but that does not work with non-writeable buffers and it looks
   like there is no Gst.Buffer.make_writeable[7] or
   Gst.MiniObject.make_writeable[8].

4. I cannot see Gst.Pad.set_caps() in the stable doc[9], I see some use
   of it in some old tests in gst-python but I don't know if they are
   actually supposed to work.

If these are indeed bugs I can file proper reports on gitlab.

Ah, I am using GStreamer 1.14.4 from Debian unstable.

Thank you,
   Antonio

[1] http://lazka.github.io/pgi-docs/GstBase-1.0/classes/Adapter.html#GstBase.Adapter.map
[2] http://lazka.github.io/pgi-docs/GstBase-1.0/classes/Adapter.html#GstBase.Adapter.take
[3] https://developer.gnome.org/gstreamer-libs/stable/GstAdapter.html#gst-adapter-map
[4] https://developer.gnome.org/gstreamer-libs/stable/GstAdapter.html#gst-adapter-take
[5] http://lazka.github.io/pgi-docs/GstBase-1.0/classes/BaseParse.html#GstBase.BaseParse.do_handle_frame
[6] https://developer.gnome.org/gstreamer-libs/stable/gstreamer-libs-GstBaseParse.html#GstBaseParseClass
[7] http://lazka.github.io/pgi-docs/Gst-1.0/classes/Buffer.html#methods
[8] http://lazka.github.io/pgi-docs/Gst-1.0/classes/MiniObject.html#methods
[9] http://lazka.github.io/pgi-docs/Gst-1.0/classes/Pad.html#methods

-- 
Antonio Ospite
https://ao2.it
https://twitter.com/ao2it

A: Because it messes up the order in which people normally read text.
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