Repository: yt-dlp/yt-dlp
File: yt_dlp/extractor/s4c.py (Python)

Code before:
        playerConfig = self._download_json(
            'https://player-api.s4c-cdn.co.uk/player-configuration/prod', video_id, query={
                'programme_id': video_id,
                'signed': '0',
                'lang': 'en',
                'mode': 'od',
                'appId': 'clic',
                'streamName': '',
            }, note='Downloading player config JSON')
        thumbnail = playerConfig['poster']
        subtitlesList = playerConfig['subtitles']
        subtitles = {}

        for i in subtitlesList:
            subtitles[i['3']] = [{'url': i['0']}]

        filename = playerConfig['filename']

        m3u8_url = self._download_json(
            'https://player-api.s4c-cdn.co.uk/streaming-urls/prod', video_id, query={
                'mode': 'od',
                'application': 'clic',
                'region': 'WW',
                'extra': 'false',
                'thirdParty': 'false',
                'filename': filename,
            }, note='Downloading streaming urls JSON')['hls']
        formats = self._extract_m3u8_formats(m3u8_url, video_id, 'mp4', m3u8_id='hls')
        return {
            'id': video_id,
            'formats': formats,
            'subtitles': subtitles,
            'thumbnail': thumbnail,
            **traverse_obj(details, ('full_prog_details', 0, {
                'title': (('programme_title', 'series_title'), {str}),
                'description': ('full_billing', {str.strip}),
                'duration': ('duration', {lambda x: int(x) * 60}),
            }), get_all=False),
        }


class S4CSeriesIE(InfoExtractor):
    _VALID_URL = r'https?://(?:www\.)?s4c\.cymru/clic/series/(?P<id>\d+)'
    _TESTS = [{
        'url': 'https://www.s4c.cymru/clic/series/864982911',
        'playlist_mincount': 6,
        'info_dict': {
            'id': '864982911',
            'title': 'Iaith ar Daith',
            'description': 'md5:e878ebf660dce89bd2ef521d7ce06397'
        },

Review comment (suggestion):
instead of using a var we can inline it in the query here
```suggestion
                'filename': player_config['filename'],
```

Code after:
        player_config = self._download_json(
            'https://player-api.s4c-cdn.co.uk/player-configuration/prod', video_id, query={
                'programme_id': video_id,
                'signed': '0',
                'lang': 'en',
                'mode': 'od',
                'appId': 'clic',
                'streamName': '',
            }, note='Downloading player config JSON')
        subtitles = {}
        for sub in traverse_obj(player_config, ('subtitles', lambda _, v: url_or_none(v['0']))):
            subtitles.setdefault(sub.get('3', 'en'), []).append({
                'url': sub['0'],
                'name': sub.get('1'),
            })
        m3u8_url = self._download_json(
            'https://player-api.s4c-cdn.co.uk/streaming-urls/prod', video_id, query={
                'mode': 'od',
                'application': 'clic',
                'region': 'WW',
                'extra': 'false',
                'thirdParty': 'false',
                'filename': player_config['filename'],
            }, note='Downloading streaming urls JSON')['hls']

        return {
            'id': video_id,
            'formats': self._extract_m3u8_formats(m3u8_url, video_id, 'mp4', m3u8_id='hls'),
            'subtitles': subtitles,
            'thumbnail': url_or_none(player_config.get('poster')),
            **traverse_obj(details, ('full_prog_details', 0, {
                'title': (('programme_title', 'series_title'), {str}),
                'description': ('full_billing', {str.strip}),
                'duration': ('duration', {lambda x: int(x) * 60}),
            }), get_all=False),
        }


class S4CSeriesIE(InfoExtractor):
    _VALID_URL = r'https?://(?:www\.)?s4c\.cymru/clic/series/(?P<id>\d+)'
    _TESTS = [{
        'url': 'https://www.s4c.cymru/clic/series/864982911',
        'playlist_mincount': 6,
        'info_dict': {
            'id': '864982911',
            'title': 'Iaith ar Daith',
            'description': 'md5:e878ebf660dce89bd2ef521d7ce06397'
        },
    }, {
        'url': 'https://www.s4c.cymru/clic/series/866852587',
        'playlist_mincount': 8,