feat(dl): add --audio-description-only and --forced-subs-only

Each keeps one kind of track inside its track type. A run of more than one title skips a title that has no such track. The REST API rejects a non-boolean value for a boolean dl param, and the DASH parser reads audio description from Role elements.

docs/dev/rest-api/endpoints.md

@@ -435,12 +435,14 @@ Make a download job. It requires `service` and `title_id`. Every other field is
 | `require_video` | string[] | `[]` | Video languages that must exist. The job fails if one is missing, even with `best_available`. |
 | `require_subs` | string[] | `[]` | Subtitle languages that must exist. The job fails if one is missing. `s_lang` still decides what to keep. |
 | `forced_subs` | boolean | `false` | Include forced subtitles. |
+| `forced_subs_only` | boolean | `false` | Download forced subtitles and no other subtitle; implies `forced_subs`. Not valid with `no_subs`, `video_only`, `audio_only` or `chapters_only`. |
 | `forced_s_lang` | string[] | `[]` | Forced subtitle language(s); implies `forced_subs`. |
 | `exact_lang` | boolean | `false` | Exact language matching. |
 | `sub_format` | string | `null` | Output subtitle format. |
 | `video_only` / `audio_only` / `subs_only` / `chapters_only` | boolean | `false` | Track-type restriction (at most one). |
 | `no_subs` / `no_audio` / `no_chapters` / `no_video` / `no_attachments` | boolean | `false` | Skip a track type. |
 | `audio_description` | boolean | `false` | Download audio description. |
+| `audio_description_only` | boolean | `false` | Download audio description and no standard audio. Not valid with `no_audio`, `video_only`, `subs_only` or `chapters_only`. |
 | `slow` | boolean/string | `null` | Randomized delay between downloads. |
 | `split_audio` | boolean | `null` | Separate files per audio codec. |
 | `skip_dl` | boolean | `false` | Only fetch keys, do not download. |

docs/dev/rest-api/remote-sessions.md

@@ -438,8 +438,9 @@ server drops an unknown codec name. An empty array is a valid value and stays
 empty.
 
 The server does not forward the `dl` mode flags: `video_only`, `audio_only`,
-`subs_only`, `chapters_only`, `list_`, `skip_dl`, `sub_format` and
-`no_attachments`. A service that reads one of them to skip work fetches more on
+`subs_only`, `chapters_only`, `list_`, `skip_dl`, `sub_format`,
+`no_attachments`, `audio_description`, `audio_description_only` and
+`forced_subs_only`. A service that reads one of them to skip work fetches more on
 the server, but the result is the same.
 
 In a client-login session (not a server account), the server gives the service

docs/guide/cli-reference.md

@@ -102,6 +102,7 @@ unshackle dl [OPTIONS] SERVICE [SERVICE ARGS...]
 | `--require-video` | - | Video langs that must exist. The title fails even with `--best-available`. Does not select tracks. |
 | `--require-subs` | - | Subtitle langs that must exist. Fails the title if one is missing. `--s-lang` still decides what to keep. |
 | `-fs`, `--forced-subs` | off | Include forced subtitle tracks. |
+| `-fso`, `--forced-subs-only` | off | Keep only forced subtitle tracks; drop the other subtitles. Implies `-fs`. |
 | `-fsl`, `--forced-s-lang` | none | Language(s) wanted for forced subtitles; implies `-fs`. A `-` prefix excludes. |
 | `--exact-lang` | off | Exact matching only: `-l es-419` matches `es-419`, not `es-ES`. Applies to selection and to sort order. |
 | `--sub-format` | - | Output subtitle format (`SRT`/`srt`, `VTT`/`webvtt`, `ASS`/`ssa`, `TTML`, `SMI`, ...), or `original` to keep the source format. |
@@ -139,6 +140,7 @@ Keep only certain track types, or skip certain track types.
 | Flag | Description |
 |---|---|
 | `-ad`, `--audio-description` | Include descriptive (audio-description) tracks. |
+| `-ado`, `--audio-description-only` | Keep only descriptive (audio-description) tracks; drop the standard audio. Does not need `-ad`. |
 | `--skip-subtitle-errors` | Skip a failed subtitle instead of aborting the title. Video/audio failures remain fatal. |
 
 ### Output, muxing & files

docs/guide/downloading.md

@@ -416,6 +416,8 @@ video track counts. `--no-audio` and `--no-video` drop the matching requirement.
   `-fs`). Works independently of `--s-lang`, so `-sl all -fsl en` grabs every full
   subtitle but only the English forced track. It accepts exclusions too: `-fsl all,-es`
   keeps every forced subtitle except the Spanish one, and `-fsl -es` means the same.
+- `-fso` / `--forced-subs-only`: keep only the forced subtitle tracks and drop every
+  other subtitle (implies `-fs`). `--s-lang` and `-fsl` still select the languages.
 - `--sub-format`: set the output subtitle format, converting only when necessary.
   Accepts codec names/values and common aliases (`srt`, `vtt`, `ass`, `ssa`, `ttml`,
   and the other codec aliases), or the literal `original` to keep the source format.
@@ -637,9 +639,29 @@ Additional track-type flags:
 
 - `-ad` / `--audio-description`: include descriptive (audio-description) tracks, which
   unshackle drops by default.
+- `-ado` / `--audio-description-only`: keep only the descriptive tracks and drop the
+  standard audio. It does not need `-ad`. Add `-A` to download no video or subtitles.
 - `--skip-subtitle-errors`: if a subtitle fails to download, skip it and continue rather
   than aborting the whole title. Video and audio failures remain fatal.
 
+!!! note "The `-only` kind flags"
+    `-ado` and `-fso` each keep one kind of track inside its track type. They do not drop
+    the other track types: `-ado` still downloads the video, and `-fso` still downloads
+    video and audio. Add `-A` or `-S` for that.
+
+    - The language flags still apply. With the default `-l orig`, `-ado` fails when the
+      descriptive track is not in the original language. Select the language with `-al`.
+    - A flag that drops the same tracks is an error, for example `-ado` with `--no-audio`
+      or `-fso` with `-A`.
+    - A title with no track of that kind stops a run of one title. A run of more than one
+      title skips that title with a warning and continues.
+    - unshackle reads the kind from the manifest or from the service. A track that
+      neither of them marks as descriptive or forced does not match.
+
+```shell title="Audio description only, in English"
+unshackle dl -A -ado -al en EXAMPLE 81234567
+```
+
 ```shell title="Subtitles only"
 unshackle dl -S -sl en EXAMPLE 81234567
 ```

docs/guide/subtitles.md

@@ -74,6 +74,7 @@ Subtitle selection happens through `dl` flags. The most important is language se
 | `-sl`, `--s-lang` | Language(s) wanted for subtitles. Defaults to `all`. A `-` prefix excludes, e.g. `all,-es`. |
 | `--require-subs` | Require these languages to exist; if present, download **all** subtitles. Cannot be combined with `--s-lang`. |
 | `-fs`, `--forced-subs` | Include forced subtitle tracks (excluded by default). |
+| `-fso`, `--forced-subs-only` | Keep only forced subtitle tracks and drop the other subtitles; implies `-fs`. |
 | `-fsl`, `--forced-s-lang` | Language(s) wanted for forced subtitles; implies `-fs`. A `-` prefix excludes. |
 | `--exact-lang` | Exact language matching, with no regional variants. |
 | `-S`, `--subs-only` | Download only subtitle tracks. |
@@ -138,6 +139,17 @@ If you pass both flags, `-fsl` wins and keeps only forced tracks in its language
 It also understands `orig` (the title's original language) and `all` (every forced
 track, same as plain `-fs`).
 
+To download the forced tracks and no other subtitle, use `-fso` / `--forced-subs-only`.
+It implies `-fs`, and `--s-lang` and `-fsl` still select the languages:
+
+```shell title="Only the English forced track"
+unshackle dl --s-lang en --forced-subs-only EXAMPLE 81234567
+```
+
+`-fso` does not drop video or audio. Add `-S` for a subtitle-only download. A title with
+no forced track stops a run of one title. A run of more than one title skips that title
+with a warning.
+
 ## Track types: forced, SDH, and CC
 
 Every subtitle track carries flags describing what kind of captions it holds. These

docs/reference/configuration/download.md

@@ -43,6 +43,9 @@ Common config keys. This is a useful subset, and every `dl` flag works:
 | `sub_format` | str | *(unset)* | Convert subtitles to this format (`srt`, `vtt`, `original`, ...). |
 | `forced_subs` | bool | `false` | Include forced subtitle tracks. |
 | `forced_s_lang` | list | `[]` | Forced subtitle language(s); implies `forced_subs`. A `-` prefix excludes. |
+| `forced_subs_only` | bool | `false` | Keep only forced subtitle tracks; implies `forced_subs`. |
+| `audio_description` | bool | `false` | Include descriptive (audio-description) tracks. |
+| `audio_description_only` | bool | `false` | Keep only descriptive (audio-description) tracks. |
 | `no_subs` / `no_audio` / `no_chapters` / `no_attachments` | bool | `false` | Skip that track type. `no_attachments` also skips attaching subtitle fonts. |
 | `downloads` | int | `1` | Tracks downloaded concurrently. |
 | `workers` | int | *(downloader default)* | Threads per track. |

tests/core/test_dash_descriptive_audio.py

@@ -37,3 +37,13 @@ def test_non_descriptive_accessibility_values(scheme: str, value: str) -> None:
 
 def test_no_accessibility_element() -> None:
     assert DASH.is_descriptive(ET.fromstring("<AdaptationSet/>")) is False
+
+
+def test_descriptive_role_element() -> None:
+    # some manifests mark audio description with a Role and no Accessibility element
+    element = ET.fromstring(
+        '<AdaptationSet><Role schemeIdUri="urn:mpeg:dash:role:2011" value="description"/></AdaptationSet>'
+    )
+    assert DASH.is_descriptive(element) is True
+    main = ET.fromstring('<AdaptationSet><Role schemeIdUri="urn:mpeg:dash:role:2011" value="main"/></AdaptationSet>')
+    assert DASH.is_descriptive(main) is False

tests/lang_selection/test_kind_only_flags.py

@@ -0,0 +1,90 @@
+"""The kind-only flags: --audio-description-only and --forced-subs-only.
+
+The filters in dl.result are not extractable without executing the whole download loop, so
+their wiring is pinned against the source, the same way test_required_langs_gate does it.
+"""
+
+from __future__ import annotations
+
+import inspect
+
+import pytest
+
+from unshackle.commands.dl import dl
+from unshackle.core.api.handlers import validate_download_parameters
+from unshackle.core.utilities import kind_only_conflict
+
+KEYS = ["audio_description_only", "forced_subs_only"]
+BASE = {"service": "EXAMPLE", "title": "x"}
+
+
+@pytest.mark.parametrize(
+    "args,only_key,base_key,expected",
+    [
+        (["-ado"], "audio_description_only", "audio_description", (True, False)),
+        (["-ad"], "audio_description_only", "audio_description", (False, True)),
+        ([], "audio_description_only", "audio_description", (False, False)),
+        (["-fso"], "forced_subs_only", "forced_subs", (True, False)),
+        (["-fs"], "forced_subs_only", "forced_subs", (False, True)),
+    ],
+)
+def test_only_flag_does_not_parse_as_its_base_flag(args, only_key, base_key, expected):
+    params = dl.cli.make_context("dl", args, resilient_parsing=True).params
+    assert (params[only_key], params[base_key]) == expected
+
+
+@pytest.mark.parametrize(
+    "params,expected",
+    [
+        ({"audio_description_only": True, "audio_only": True}, None),
+        ({"audio_description_only": True}, None),
+        ({"audio_description_only": True, "no_audio": True}, ("audio_description_only", "no_audio")),
+        ({"audio_description_only": True, "video_only": True}, ("audio_description_only", "video_only")),
+        ({"forced_subs_only": True, "subs_only": True}, None),
+        ({"forced_subs_only": True, "no_subs": True}, ("forced_subs_only", "no_subs")),
+        ({"forced_subs_only": True, "audio_only": True}, ("forced_subs_only", "audio_only")),
+        ({"no_audio": True, "video_only": True}, None),
+        # the *_only track-type flags combine: -A -S keeps audio, so -ado is not dropped
+        ({"audio_description_only": True, "audio_only": True, "subs_only": True}, None),
+        ({"forced_subs_only": True, "subs_only": True, "audio_only": True}, None),
+        ({"audio_description_only": True, "subs_only": True}, ("audio_description_only", "subs_only")),
+    ],
+)
+def test_kind_only_conflict(params, expected):
+    assert kind_only_conflict(params) == expected
+
+
+def test_api_rejects_a_conflict():
+    assert validate_download_parameters({**BASE, "audio_description_only": True, "no_audio": True}) == (
+        "Cannot use both audio_description_only and no_audio"
+    )
+    assert validate_download_parameters({**BASE, "audio_description_only": True, "audio_only": True}) is None
+
+
+@pytest.mark.parametrize("key", [*KEYS, "audio_description", "audio_only"])
+def test_api_rejects_a_non_boolean_flag(key):
+    # the string "false" is truthy in dl.result, so it would turn the flag on
+    assert validate_download_parameters({**BASE, key: "false"}) == f"{key} must be a boolean"
+    assert validate_download_parameters({**BASE, key: None}) is None
+
+
+class TestFilterWiring:
+    source = inspect.getsource(dl.result)
+
+    def test_ado_runs_when_the_title_has_no_separate_audio(self):
+        # embedded audio is standard audio: the filter must sit before the `len(...) > 0` guard
+        ado = self.source.index("if keep_audio and audio_description_only:")
+        guard = self.source.index("if keep_audio and len(title.tracks.audio) > 0:")
+        assert ado < guard
+
+    def test_ado_does_not_count_embedded_audio(self):
+        # both the --require-audio gate and the missing-language check
+        assert self.source.count("keep_videos and not audio_description_only") == 2
+
+    def test_only_filters_keep_one_kind(self):
+        assert "title.tracks.select_audio(lambda x: x.descriptive)" in self.source
+        assert "title.tracks.select_subtitles(lambda x: x.forced)" in self.source
+
+    def test_fso_implies_forced_subs(self):
+        # services read forced_subs from the ctx params to fetch forced tracks at all
+        assert "if forced_s_lang or fsl_excl or forced_subs_only:" in self.source

tests/lang_selection/test_kind_only_selection.py

@@ -0,0 +1,149 @@
+"""Run the kind-only filters through the real dl.result() selection loop.
+
+A fake service hands in-memory tracks to the loop, and the run stops at the first
+title that reaches ``Tracks.tree``, the step right after selection. A title with no
+track of the kind never gets there, so what the hook records is what the run kept.
+"""
+
+from __future__ import annotations
+
+import inspect
+import logging
+from typing import Any, cast
+
+import pytest
+
+from unshackle.commands.dl import dl
+from unshackle.core.api.handlers import DEFAULT_DOWNLOAD_PARAMS
+from unshackle.core.service import Service
+from unshackle.core.titles import Episode, Series
+from unshackle.core.tracks import Audio, Subtitle, Tracks, Video
+
+
+class Selected(BaseException):
+    """Carries the kept track ids out of the loop."""
+
+    def __init__(self, tracks: Tracks) -> None:
+        self.ids = {
+            "video": [t.id for t in tracks.videos],
+            "audio": [t.id for t in tracks.audio],
+            "subs": [t.id for t in tracks.subtitles],
+        }
+
+
+class Harness(dl):
+    def __getattr__(self, name: str) -> None:
+        # every optional dl attribute (tmdb ids, cdm, vaults, ...) reads as unset
+        return None
+
+
+class FakeService:
+    """One episode per entry; ``ad`` adds a descriptive track, ``forced`` a forced subtitle."""
+
+    def __init__(self, episodes: dict[int, dict[str, bool]]) -> None:
+        self.episodes = episodes
+        self.session = None
+
+    def authenticate(self, cookies: Any = None, credential: Any = None) -> None:
+        pass
+
+    def get_titles_cached(self) -> Series:
+        return Series(
+            Episode(id_=f"show-s01-e{n:03}", service=FakeService, title="Show", season=1, number=n, language="en")
+            for n in self.episodes
+        )
+
+    def get_tracks(self, title: Episode) -> Tracks:
+        kinds = self.episodes[title.number]
+        tracks = Tracks()
+        tracks.add(Video(id_="v", url="https://x/v", language="en", codec=Video.Codec.AVC, range_=Video.Range.SDR))
+        tracks.add(Audio(id_="a", url="https://x/a", language="en", codec=Audio.Codec.AAC, bitrate=128_000))
+        if kinds.get("ad"):
+            tracks.add(
+                Audio(id_="ad", url="https://x/ad", language="en", codec=Audio.Codec.AAC, bitrate=1, descriptive=True)
+            )
+        tracks.add(Subtitle(id_="s", url="https://x/s", language="en", codec=Subtitle.Codec.WebVTT))
+        if kinds.get("forced"):
+            tracks.add(Subtitle(id_="sf", url="https://x/sf", language="en", codec=Subtitle.Codec.WebVTT, forced=True))
+        return tracks
+
+    def get_chapters(self, title: Episode) -> list:
+        return []
+
+    def __getattr__(self, name: str) -> Any:
+        if name.startswith("on_"):
+            # the event hooks (on_track_downloaded, ...) the loop subscribes
+            return lambda *a, **k: None
+        raise AttributeError(name)
+
+
+def run(monkeypatch: pytest.MonkeyPatch, caplog: pytest.LogCaptureFixture, episodes: dict, **flags: Any) -> Any:
+    """Return the Selected ids, the exit code, or None for a run that completes."""
+    monkeypatch.setattr(Tracks, "tree", lambda self, *a, **k: (_ for _ in ()).throw(Selected(self)))
+    cmd = Harness.__new__(Harness)
+    cmd.log = logging.getLogger("test_kind_only")
+    cmd.service = "FAKE"
+    cmd.tmdb_searched = True
+    cmd.completed_files = []
+    kwargs: dict[str, Any] = {}
+    for name, param in inspect.signature(dl.result).parameters.items():
+        if name in DEFAULT_DOWNLOAD_PARAMS:
+            kwargs[name] = DEFAULT_DOWNLOAD_PARAMS[name]
+        elif name not in ("self", "service"):
+            kwargs[name] = None if param.default is inspect.Parameter.empty else param.default
+    kwargs.update(quality=[], vcodec=[], acodec=[], range_=[], wanted=[], cdm_only=None, downloads=1)
+    kwargs.update(flags)
+    caplog.set_level(logging.WARNING, logger="test_kind_only")
+    try:
+        cmd.result(cast(Service, FakeService(episodes)), **kwargs)
+    except Selected as sel:
+        return sel.ids
+    except SystemExit as exc:
+        return exc.code
+    return None
+
+
+def test_ado_keeps_the_descriptive_track_and_the_other_types(
+    monkeypatch: pytest.MonkeyPatch, caplog: pytest.LogCaptureFixture
+) -> None:
+    ids = run(monkeypatch, caplog, {1: {"ad": True, "forced": True}}, audio_description_only=True)
+    assert ids == {"video": ["v"], "audio": ["ad"], "subs": ["s"]}
+
+
+def test_fso_keeps_the_forced_track_and_the_other_types(
+    monkeypatch: pytest.MonkeyPatch, caplog: pytest.LogCaptureFixture
+) -> None:
+    ids = run(monkeypatch, caplog, {1: {"ad": True, "forced": True}}, forced_subs_only=True)
+    assert ids == {"video": ["v"], "audio": ["a"], "subs": ["sf"]}
+
+
+def test_only_flags_with_their_type_flags_give_a_single_kind(
+    monkeypatch: pytest.MonkeyPatch, caplog: pytest.LogCaptureFixture
+) -> None:
+    ids = run(monkeypatch, caplog, {1: {"ad": True, "forced": True}}, audio_description_only=True, audio_only=True)
+    assert ids == {"video": [], "audio": ["ad"], "subs": []}
+    ids = run(monkeypatch, caplog, {1: {"ad": True, "forced": True}}, forced_subs_only=True, subs_only=True)
+    assert ids == {"video": [], "audio": [], "subs": ["sf"]}
+
+
+@pytest.mark.parametrize("flag", ["audio_description_only", "forced_subs_only"])
+def test_a_single_title_with_no_such_track_exits(
+    monkeypatch: pytest.MonkeyPatch, caplog: pytest.LogCaptureFixture, flag: str
+) -> None:
+    assert run(monkeypatch, caplog, {1: {}}, **{flag: True}) == 1
+    assert "Skipping" not in caplog.text
+
+
+def test_a_multi_title_run_skips_the_title_and_continues(
+    monkeypatch: pytest.MonkeyPatch, caplog: pytest.LogCaptureFixture
+) -> None:
+    ids = run(monkeypatch, caplog, {1: {}, 2: {"ad": True}}, audio_description_only=True)
+    assert ids["audio"] == ["ad"]
+    assert "Skipping Show S01E01" in caplog.text
+
+
+def test_a_multi_title_run_with_every_title_skipped_completes(
+    monkeypatch: pytest.MonkeyPatch, caplog: pytest.LogCaptureFixture
+) -> None:
+    assert run(monkeypatch, caplog, {1: {}, 2: {}}, forced_subs_only=True) is None
+    assert caplog.text.count("Skipping Show S01E") == 2

tests/lang_selection/test_required_langs.py

@@ -5,6 +5,7 @@ import inspect
 import pytest
 
 from unshackle.commands.dl import dl
+from unshackle.core.api import download_manager
 from unshackle.core.api.handlers import DEFAULT_DOWNLOAD_PARAMS
 from unshackle.core.utilities import missing_required_langs
 
@@ -102,15 +103,15 @@ def test_api_accepts_the_require_flags():
     )
 
 
-@pytest.mark.parametrize("key", ["require_audio", "require_video"])
-def test_api_reaches_dl_result(key, monkeypatch):
+@pytest.mark.parametrize(
+    "key,default",
+    [("require_audio", []), ("require_video", []), ("audio_description_only", False), ("forced_subs_only", False)],
+)
+def test_api_reaches_dl_result(key, default):
     # download_manager builds the dl.result kwargs by hand, so a missing key is a silent drop
-    import inspect as _inspect
-
-    from unshackle.core.api import download_manager
-
-    source = _inspect.getsource(download_manager)
-    assert f'{key}=params.get("{key}", [])' in source
+    assert DEFAULT_DOWNLOAD_PARAMS[key] == default
+    assert key in inspect.signature(dl.result).parameters
+    assert f'{key}=params.get("{key}", {default!r})' in inspect.getsource(download_manager)
 
 
 @pytest.mark.parametrize(

tests/lang_selection/test_required_langs_gate.py

@@ -48,7 +48,7 @@ class TestGateWiring:
         assert "require_video if keep_videos else []" in self.source
 
     def test_gate_counts_audio_embedded_in_kept_video(self):
-        assert "embedded_audio_langs(title.tracks.videos, keep_videos)" in self.source
+        assert "embedded_audio_langs(title.tracks.videos, keep_videos and not audio_description_only)" in self.source
 
     def test_gate_honours_exact_lang(self):
         assert "missing_required_langs(required, available, title.language, exact=exact_lang)" in self.source

unshackle/commands/dl.py

@@ -93,6 +93,7 @@ from unshackle.core.utilities import (
     is_close_match,
     is_exact_match,
     keep_forced_subtitle,
+    kind_only_conflict,
     log_event,
     missing_required_langs,
     partition_exclusions,
@@ -756,6 +757,13 @@ class dl:
         help="Subtitle languages that must exist. The title fails if one is missing. -sl still decides what to keep.",
     )
     @click.option("-fs", "--forced-subs", is_flag=True, default=False, help="Include forced subtitle tracks.")
+    @click.option(
+        "-fso",
+        "--forced-subs-only",
+        is_flag=True,
+        default=False,
+        help="Download forced subtitle tracks and no other subtitle tracks.",
+    )
     @click.option(
         "-fsl",
         "--forced-s-lang",
@@ -882,6 +890,13 @@ class dl:
         help="Do not download or mux attachments (cover art, subtitle fonts, and files the service attaches).",
     )
     @click.option("-ad", "--audio-description", is_flag=True, default=False, help="Download audio description tracks.")
+    @click.option(
+        "-ado",
+        "--audio-description-only",
+        is_flag=True,
+        default=False,
+        help="Download audio description tracks and no standard audio tracks.",
+    )
     @click.option(
         "--slow",
         type=SLOW_DELAY_RANGE,
@@ -1523,6 +1538,7 @@ class dl:
         require_video: list[str],
         require_subs: list[str],
         forced_subs: bool,
+        forced_subs_only: bool,
         forced_s_lang: list[str],
         exact_lang: bool,
         sub_format: Optional[Union[Subtitle.Codec, str]],
@@ -1537,6 +1553,7 @@ class dl:
         no_video: bool,
         no_attachments: bool,
         audio_description: bool,
+        audio_description_only: bool,
         slow: Optional[tuple[int, int]],
         list_: bool,
         list_titles: bool,
@@ -1639,7 +1656,27 @@ class dl:
                 if excludes and name in parent_params:
                     parent_params[name] = includes
 
-        if forced_s_lang or fsl_excl:
+        conflict = kind_only_conflict(
+            {
+                "audio_description_only": audio_description_only,
+                "forced_subs_only": forced_subs_only,
+                "no_audio": no_audio,
+                "no_subs": no_subs,
+                "video_only": video_only,
+                "audio_only": audio_only,
+                "subs_only": subs_only,
+                "chapters_only": chapters_only,
+            }
+        )
+        if conflict:
+            first, second = (f"--{name.replace('_', '-')}" for name in conflict)
+            self.log.error(f"{first} cannot be used with {second}: {second} drops the tracks that {first} selects.")
+            sys.exit(1)
+
+        if audio_description_only:
+            audio_description = True
+
+        if forced_s_lang or fsl_excl or forced_subs_only:
             # services read forced_subs from raw ctx params, so the implication must be pushed there too
             forced_subs = True
             if "all" in forced_s_lang:
@@ -2044,6 +2081,27 @@ class dl:
         post_script_last: dict[Any, dict[Path, dict[str, str]]] = {}
         post_script_folders: list[Path] = []
         post_script_sample: dict[str, str] = {}
+        wanted_total = sum(post_script_pending.values())
+
+        def settle_post_script_group(title: Any) -> None:
+            """Count one title of its group as done; send the season event after the last one."""
+            group_key = post_script_group(title)
+            post_script_pending[group_key] = post_script_pending.get(group_key, 1) - 1
+            if post_script_pending[group_key] <= 0:
+                for folder, context in post_script_last.get(group_key, {}).items():
+                    dispatch("success", "season", season_context(context, folder), postscript)
+
+        def skip_title(title: Any, reason: str) -> None:
+            """Skip a title that has no track of the kind an only flag selects.
+
+            A run with one title stops instead, because it has nothing else to download.
+            """
+            if wanted_total <= 1:
+                self.log.error(reason)
+                sys.exit(1)
+            self.log.warning(f"{reason} Skipping {title}")
+            if not no_mux:
+                settle_post_script_group(title)
 
         for i, title in enumerate(titles):
             v_lang, a_lang, s_lang, range_ = base_selection
@@ -2316,13 +2374,14 @@ class dl:
                 (
                     "audio",
                     require_audio if keep_audio else [],
-                    [a.language for a in title.tracks.audio] + embedded_audio_langs(title.tracks.videos, keep_videos),
+                    [a.language for a in title.tracks.audio if a.descriptive or not audio_description_only]
+                    + embedded_audio_langs(title.tracks.videos, keep_videos and not audio_description_only),
                 ),
                 ("video", require_video if keep_videos else [], [v.language for v in title.tracks.videos]),
                 (
                     "subtitle",
                     require_subs if keep_subtitles else [],
-                    [t.language for t in title.tracks.subtitles],
+                    [t.language for t in title.tracks.subtitles if t.forced or not forced_subs_only],
                 ),
             ):
                 missing_required = missing_required_langs(required, available, title.language, exact=exact_lang)
@@ -2749,7 +2808,17 @@ class dl:
                                 fsl_excl_r, [t.language for t in title.tracks.subtitles if t.forced], exact_lang
                             )
                             title.tracks.select_subtitles(lambda x: not (x.forced and str(x.language) in drop))
+                        if forced_subs_only:
+                            title.tracks.select_subtitles(lambda x: x.forced)
+                            if not title.tracks.subtitles:
+                                skip_title(title, "There's no forced subtitle track for the selected languages.")
+                                continue
 
+                if keep_audio and audio_description_only:
+                    title.tracks.select_audio(lambda x: x.descriptive)
+                    if not title.tracks.audio:
+                        skip_title(title, "There's no audio description track.")
+                        continue
                 # might have no audio tracks if part of the video, e.g. transport stream hls
                 if keep_audio and len(title.tracks.audio) > 0:
                     if not audio_description:
@@ -2818,7 +2887,10 @@ class dl:
                         if a_orig_token in audio_languages:
                             a_orig_token = None
 
-                        embedded_langs = embedded_audio_langs(title.tracks.videos, keep_videos)
+                        embedded_langs = embedded_audio_langs(
+                            title.tracks.videos, keep_videos and not audio_description_only
+                        )
+                        audio_noun = "audio description tracks" if audio_description_only else "audio tracks"
 
                         if not any(tok in processed_lang for tok in ("best", "all")):
                             missing_a_langs = find_missing_langs(
@@ -2832,17 +2904,17 @@ class dl:
                                     remaining = [tok for tok in processed_lang if tok not in missing_a_langs]
                                     if remaining:
                                         self.log.warning(
-                                            f"{missing_str} not found in audio tracks, "
+                                            f"{missing_str} not found in {audio_noun}, "
                                             f"continuing with: {as_requested(remaining, a_orig_token)}"
                                         )
                                         processed_lang = remaining
                                     else:
                                         self.log.error(
-                                            f"{missing_str} not found in audio tracks and no fallback available"
+                                            f"{missing_str} not found in {audio_noun} and no fallback available"
                                         )
                                         sys.exit(1)
                                 else:
-                                    self.log.error(missing_str + " not found in audio tracks")
+                                    self.log.error(f"{missing_str} not found in {audio_noun}")
                                     sys.exit(1)
 
                         title.tracks.audio = select_best_audio(
@@ -3700,11 +3772,7 @@ class dl:
                             post_script_folders.append(final_path.parent)
 
                 if not no_mux:
-                    group_key = post_script_group(title)
-                    post_script_pending[group_key] = post_script_pending.get(group_key, 1) - 1
-                    if post_script_pending[group_key] <= 0:
-                        for folder, context in post_script_last.get(group_key, {}).items():
-                            dispatch("success", "season", season_context(context, folder), postscript)
+                    settle_post_script_group(title)
 
                 title_dl_time = time_elapsed_since(dl_start_time)
                 downloaded_label = "Track" if isinstance(title, Song) else "Title"

unshackle/core/api/download_manager.py

@@ -601,6 +601,7 @@ def perform_download(
                 require_video=params.get("require_video", []),
                 require_subs=params.get("require_subs", []),
                 forced_subs=ctx.params["forced_subs"],
+                forced_subs_only=params.get("forced_subs_only", False),
                 forced_s_lang=params.get("forced_s_lang", []),
                 exact_lang=params.get("exact_lang", False),
                 sub_format=params.get("sub_format"),
@@ -615,6 +616,7 @@ def perform_download(
                 no_video=params.get("no_video", False),
                 no_attachments=params.get("no_attachments", False),
                 audio_description=params.get("audio_description", False),
+                audio_description_only=params.get("audio_description_only", False),
                 slow=params.get("slow", None),
                 list_=False,
                 list_titles=False,

unshackle/core/api/handlers.py

@@ -33,7 +33,7 @@ from unshackle.core.proxies.resolve import initialize_proxy_providers, resolve_p
 from unshackle.core.services import Services
 from unshackle.core.titles import Episode, Movie, Song, Title_T
 from unshackle.core.tracks import Audio, Subtitle, Tracks, Video
-from unshackle.core.utilities import declared_kwargs
+from unshackle.core.utilities import declared_kwargs, kind_only_conflict
 from unshackle.core.utils.click_types import AUDIO_CODEC_LIST, SUBTITLE_CODEC, VIDEO_CODEC_LIST
 from unshackle.core.utils.collections import ci_get
 from unshackle.core.utils.redact import REDACTED, URL_USERINFO_RE, redact_all, redact_secrets, redact_text
@@ -64,6 +64,7 @@ DEFAULT_DOWNLOAD_PARAMS = {
     "require_video": [],
     "require_subs": [],
     "forced_subs": False,
+    "forced_subs_only": False,
     "forced_s_lang": [],
     "exact_lang": False,
     "sub_format": None,
@@ -77,6 +78,7 @@ DEFAULT_DOWNLOAD_PARAMS = {
     "no_video": False,
     "no_attachments": False,
     "audio_description": False,
+    "audio_description_only": False,
     "slow": None,
     "split_audio": None,
     "skip_dl": False,
@@ -1925,6 +1927,13 @@ def validate_download_parameters(data: Dict[str, Any]) -> Optional[str]:
         return "Cannot use both no_subs and subs_only"
     if data.get("no_audio") and data.get("audio_only"):
         return "Cannot use both no_audio and audio_only"
+    conflict = kind_only_conflict(data)
+    if conflict:
+        return f"Cannot use both {conflict[0]} and {conflict[1]}"
+
+    for key, default in DEFAULT_DOWNLOAD_PARAMS.items():
+        if isinstance(default, bool) and data.get(key) is not None and not isinstance(data[key], bool):
+            return f"{key} must be a boolean"
 
     for key in ("require_audio", "require_video", "require_subs"):
         value = data.get(key)

unshackle/core/api/routes.py

@@ -895,6 +895,9 @@ async def download(request: web.Request) -> web.Response:
               forced_subs:
                 type: boolean
                 description: Include forced subtitle tracks (default - false)
+              forced_subs_only:
+                type: boolean
+                description: Download forced subtitle tracks and no other subtitle tracks, implies forced_subs (default - false)
               forced_s_lang:
                 type: array
                 items:
@@ -936,6 +939,9 @@ async def download(request: web.Request) -> web.Response:
               audio_description:
                 type: boolean
                 description: Download audio description tracks (default - false)
+              audio_description_only:
+                type: boolean
+                description: Download audio description tracks and no standard audio tracks (default - false)
               slow:
                 oneOf:
                   - type: boolean

unshackle/core/manifests/dash.py

@@ -1209,7 +1209,7 @@ class DASH:
                 ("urn:mpeg:dash:role:2011", "descriptive"),
                 ("urn:tva:metadata:cs:AudioPurposeCS:2007", "1"),
             )
-            for x in adaptation_set.findall("Accessibility")
+            for x in (*adaptation_set.findall("Accessibility"), *adaptation_set.findall("Role"))
         )
 
     @staticmethod

unshackle/core/utilities.py

@@ -17,7 +17,7 @@ from collections import defaultdict
 from datetime import datetime, timezone
 from pathlib import Path
 from types import ModuleType
-from typing import Any, Callable, Optional, Sequence, Union
+from typing import Any, Callable, Mapping, Optional, Sequence, Union
 from urllib.parse import ParseResult, urlparse
 from uuid import uuid4
 
@@ -235,6 +235,29 @@ def keep_forced_subtitle(
     return match_func(language, forced_s_lang)
 
 
+def kind_only_conflict(params: Mapping[str, Any]) -> Optional[tuple[str, str]]:
+    """
+    Return the first (kind-only flag, flag that drops its track type) pair that are both set.
+
+    The ``*_only`` track-type flags combine, so another one only drops the kind-only
+    flag's track type when its own ``*_only`` flag is not set as well.
+    """
+    for flag, own_only, no_flag in (
+        ("audio_description_only", "audio_only", "no_audio"),
+        ("forced_subs_only", "subs_only", "no_subs"),
+    ):
+        if not params.get(flag):
+            continue
+        if params.get(no_flag):
+            return flag, no_flag
+        if params.get(own_only):
+            continue
+        for other in ("video_only", "audio_only", "subs_only", "chapters_only"):
+            if params.get(other):
+                return flag, other
+    return None
+
+
 def embedded_audio_langs(videos: Sequence[Any], keep_videos: bool) -> list[str]:
     """
     Return the audio languages carried inside video tracks rather than beside them.