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

[Marvin Scholz]

On 21 Sep 2020, at 11:15, Steve Lhomme wrote:

> 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.

Using a venv does not seem very useful here.
If packagers want to do that, thats a different story but
in general I dont think VLC should set up a venv because
it does not even install any dependency so it seems pointless
to do.
Even if we were to package it in contribs, a venv is probably
not needed as it seems youtube-dl has no dependencies itself
so it could just be easily imported without a venv.

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