How to use the wagtailvideos.ffmpeg function in wagtailvideos

def ffmpeg_check(app_configs, **kwargs):
    messages = []
    if not ffmpeg.installed():
        messages.append(
            Warning(
                'ffmpeg could not be found on your system. Transcoding will be disabled',
                hint=None,
                id='wagtailvideos.W001',
            )
        )
    return messages

else:
        form = VideoForm(instance=video)

    if not video._meta.get_field('file').storage.exists(video.file.name):
        # Give error if image file doesn't exist
        messages.error(request, _(
            "The source video file could not be found. Please change the source or delete the video."
        ).format(video.title), buttons=[
            messages.button(reverse('wagtailvideos:delete', args=(video.id,)), _('Delete'))
        ])

    return render(request, "wagtailvideos/videos/edit.html", {
        'video': video,
        'form': form,
        'filesize': video.get_file_size(),
        'can_transcode': ffmpeg.installed(),
        'transcodes': video.transcodes.all(),
        'transcode_form': VideoTranscodeAdminForm(video=video),
        'user_can_delete': permission_policy.user_has_permission_for_instance(request.user, 'delete', video)
    })

def video_saved(sender, instance, **kwargs):
    if not ffmpeg.installed():
        return

    if hasattr(instance, '_from_signal'):
        return

    has_changed = instance._initial_file is not instance.file
    filled_out = instance.thumbnail is not None and instance.duration is not None
    if has_changed or not filled_out:
        with get_local_file(instance.file) as file_path:
            if has_changed or instance.thumbnail is None:
                instance.thumbnail = ffmpeg.get_thumbnail(file_path)

            if has_changed or instance.duration is None:
                instance.duration = ffmpeg.get_duration(file_path)

    instance.file_size = instance.file.size