[vlc-devel] [PATCH 1/2] share: add wrapper script for the YoutubeDL Python module

[Steve Lhomme]

On 2020-09-21 10:54, Marvin Scholz wrote:
> 
> 
> On 21 Sep 2020, at 10:51, Steve Lhomme wrote:
> 
>> On 2020-09-21 10:39, Marvin Scholz wrote:
>>>
>>>
>>> On 21 Sep 2020, at 10:38, Steve Lhomme wrote:
>>>
>>>> On 2020-09-21 10:36, Marvin Scholz wrote:
>>>>>
>>>>>
>>>>> On 21 Sep 2020, at 10:34, Steve Lhomme wrote:
>>>>>
>>>>>> On 2020-09-21 10:30, Marvin Scholz wrote:
>>>>>>>
>>>>>>>
>>>>>>> On 21 Sep 2020, at 10:22, Steve Lhomme wrote:
>>>>>>>
>>>>>>>> On 2020-09-20 20:57, Rémi Denis-Courmont wrote:
>>>>>>>>> This script generates a M3U playlist from a given URL, providing a
>>>>>>>>> simple serial format that can be read and parsed by another 
>>>>>>>>> process.
>>>>>>>>>
>>>>>>>>> There are in principles two other alternative ways to access it:
>>>>>>>>>
>>>>>>>>> 1) Calling the YoutubeDL module directly in-process through 
>>>>>>>>> CPython.
>>>>>>>>>     This poses a number of problems:
>>>>>>>>>     - CPython must be loaded by the main executable. Python 
>>>>>>>>> modules will
>>>>>>>>>       fail to resolve their CPython symbols otherwise.
>>>>>>>>>     - Multiple CPython interpreters are still very immature; 
>>>>>>>>> GIL behaves
>>>>>>>>>       weirdly. CPython is really not meant for multithread.
>>>>>>>>>     - The GIL prevents concurrent uses (that's the whole point 
>>>>>>>>> of it).
>>>>>>>>>     - CPython network I/O cannot be interrupted by VLC 
>>>>>>>>> interruptions, so
>>>>>>>>>       the calling thread may get stuck inside CPython.
>>>>>>>>>     - A build-time dependency on CPython is added.
>>>>>>>>>
>>>>>>>>> 2) Parsing the output of the youtube-dl program. This is what 
>>>>>>>>> MPV does.
>>>>>>>>>     But this requires a whole new parser for the Python syntax.
>>>>>>>>>
>>>>>>>>> With a custom Python script, we can decide on the serialisation 
>>>>>>>>> format
>>>>>>>>> that most suits the usage.
>>>>>>>>> ---
>>>>>>>>>   share/Makefile.am     |   2 +
>>>>>>>>>   share/ytdl-extract.py | 103 
>>>>>>>>> ++++++++++++++++++++++++++++++++++++++++++
>>>>>>>>>   2 files changed, 105 insertions(+)
>>>>>>>>>   create mode 100755 share/ytdl-extract.py
>>>>>>>>>
>>>>>>>>> diff --git a/share/Makefile.am b/share/Makefile.am
>>>>>>>>> index 2373ffbe91..8a92f04360 100644
>>>>>>>>> --- a/share/Makefile.am
>>>>>>>>> +++ b/share/Makefile.am
>>>>>>>>> @@ -49,6 +49,8 @@ nobase_dist_pkgdata_SCRIPTS = \
>>>>>>>>>       utils/audio-vlc-default.sh \
>>>>>>>>>       utils/video-vlc-default.sh \
>>>>>>>>>       $(NULL)
>>>>>>>>> +
>>>>>>>>> +dist_pkgdata_SCRIPTS = ytdl-extract.py
>>>>>>>>>   endif
>>>>>>>>>    EXTRA_DIST += \
>>>>>>>>> diff --git a/share/ytdl-extract.py b/share/ytdl-extract.py
>>>>>>>>> new file mode 100755
>>>>>>>>> index 0000000000..2d784c5090
>>>>>>>>> --- /dev/null
>>>>>>>>> +++ b/share/ytdl-extract.py
>>>>>>>>> @@ -0,0 +1,103 @@
>>>>>>>>> +#! /usr/bin/python3
>>>>>>>>> +#
>>>>>>>>> +# Copyright (C) 2020 Rémi Denis-Courmont
>>>>>>>>> +#
>>>>>>>>> +# This program is free software; you can redistribute it 
>>>>>>>>> and/or modify it
>>>>>>>>> +# under the terms of the GNU Lesser General Public License as 
>>>>>>>>> published by
>>>>>>>>> +# the Free Software Foundation; either version 2.1 of the 
>>>>>>>>> License, or
>>>>>>>>> +# (at your option) any later version.
>>>>>>>>> +#
>>>>>>>>> +# This program is distributed in the hope that it will be useful,
>>>>>>>>> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
>>>>>>>>> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>>>>>>>>> +# GNU Lesser General Public License for more details.
>>>>>>>>> +#
>>>>>>>>> +# You should have received a copy of the GNU Lesser General 
>>>>>>>>> Public License
>>>>>>>>> +# along with this program; if not, write to the Free Software 
>>>>>>>>> Foundation,
>>>>>>>>> +# Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, 
>>>>>>>>> USA.
>>>>>>>>> +
>>>>>>>>> +import sys
>>>>>>>>> +import youtube_dl
>>>>>>>>
>>>>>>>> How does this work if the import library is not there ? Do we 
>>>>>>>> have requirements on the version of the library ? Can we check 
>>>>>>>> it in configure.ac ?
>>>>>>>
>>>>>>> Checking it in configure.ac seems useless as this is about the 
>>>>>>> host system, not a build time requirement.
>>>>>>> If the library is not there or its the wrong version so API does 
>>>>>>> not match, it the script would just fail
>>>>>>> which IIUC is handled properly by the access module calling the 
>>>>>>> script.
>>>>>>>
>>>>>>>> Can it be part of contribs ?
>>>>>>>
>>>>>>> Could be possible, but IMO out of scope of this patchset.
>>>>>>>
>>>>>>>> Should we run python with out local environment with our little 
>>>>>>>> set of dependencies ?
>>>>>>>
>>>>>>> Why would you want to do that? I dont really see any benefit 
>>>>>>> doing so while possibly
>>>>>>> breaking the import.
>>>>>>
>>>>>> I think it's the opposite. Using the system dependencies might be 
>>>>>> the one breaking the version we support.
>>>>>
>>>>> Not sure what you mean by "version we support" as we rely on the 
>>>>> system-installed
>>>>> youtube-dl here. Worst case the API is different and it fails?
>>>>
>>>> If the youtube-dl of the system changes with a different API or way 
>>>> or working that we support it breaks the feature in VLC. If we have 
>>>> our local version of youtube-dl we don't have this problem.
>>>
>>> We don't have a "local" version of youtube-dl though
>>
>> My question was:
>> Should we run python with out local environment with our little set of 
>> dependencies ?
> 
> Ok, I dont understand what you mean by that then, sorry.

Virtual Environment
https://docs.python.org/3/tutorial/venv.html

The other thing is that whatever VLC needs, it doesn't pollute the 
system environment, potentially introducing incompatible dependencies.