plugins.twitch: add --twitch-supported-codecs

Add the temporary `--twitch-supported-codecs` plugin argument
for being able to set the client's video codec preference.

Set the default value to "h264" to ensure that no compatibility
issues arise on clients without AV1/HEVC decode capabilities.

src/streamlink/plugins/twitch.py

@@ -204,18 +204,26 @@ def __init__(self, *args, disable_ads: bool = False, low_latency: bool = False,
 
 
 class UsherService:
-    def __init__(self, session):
+    _SUPPORTED_CODECS = "h264", "h265", "av1"
+
+    def __init__(self, session: Streamlink, supported_codecs: Optional[str] = None):
         self.session = session
+        self.supported_codecs = ",".join(sorted({
+            codec for codec in (supported_codecs or "").split(",") if codec in self._SUPPORTED_CODECS
+        })) or self._SUPPORTED_CODECS[0]
 
     def _create_url(self, endpoint, **extra_params):
         url = f"https://usher.ttvnw.net{endpoint}"
         params = {
+            "platform": "web",
             "player": "twitchweb",
             "p": int(random() * 999999),
             "type": "any",
             "allow_source": "true",
             "allow_audio_only": "true",
             "allow_spectre": "false",
+            "playlist_include_framerate": "true",
+            "supported_codecs": self.supported_codecs,
         }
         params.update(extra_params)
 
@@ -652,6 +660,17 @@ def decode_client_integrity_token(data: str, schema: Optional[validate.Schema] =
         Regular streams can cause buffering issues with this option enabled due to the reduced --hls-live-edge value.
     """,
 )
+@pluginargument(
+    "supported-codecs",
+    help="""
+        A comma-separated list of codec names which signals Twitch the client's stream codec preference.
+        Which streams and which codecs are available depends on the specific channel and broadcast.
+
+        Default is "h264".
+
+        Supported codecs are "h264", "h265", "av1". Set to "h264,h265,av1" to enable all codecs.
+    """,
+)
 @pluginargument(
     "api-header",
     metavar="KEY=VALUE",
@@ -719,7 +738,10 @@ def __init__(self, *args, **kwargs):
             api_header=self.get_option("api-header"),
             access_token_param=self.get_option("access-token-param"),
         )
-        self.usher = UsherService(session=self.session)
+        self.usher = UsherService(
+            session=self.session,
+            supported_codecs=self.get_option("supported-codecs"),
+        )
 
         def method_factory(parent_method):
             def inner():

tests/plugins/test_twitch.py

@@ -10,7 +10,14 @@
 from streamlink import Streamlink
 from streamlink.exceptions import NoStreamsError, PluginError
 from streamlink.options import Options
-from streamlink.plugins.twitch import Twitch, TwitchAPI, TwitchHLSStream, TwitchHLSStreamReader, TwitchHLSStreamWriter
+from streamlink.plugins.twitch import (
+    Twitch,
+    TwitchAPI,
+    TwitchHLSStream,
+    TwitchHLSStreamReader,
+    TwitchHLSStreamWriter,
+    UsherService,
+)
 from tests.mixins.stream_hls import EventedHLSStreamWriter, Playlist, Segment as _Segment, Tag, TestMixinStreamHLS
 from tests.plugins import PluginCanHandleUrl
 from tests.resources import text
@@ -397,6 +404,21 @@ def test_hls_low_latency_no_ads_reload_time(self):
         assert self.thread.reader.worker.playlist_reload_time == pytest.approx(23 / 3)
 
 
+@pytest.mark.parametrize(("supported_codecs", "expected"), [
+    pytest.param(None, "h264", id="Default"),
+    pytest.param("foo", "h264", id="Invalid"),
+    pytest.param("h264", "h264", id="h264"),
+    pytest.param("h265", "h265", id="h265"),
+    pytest.param("av1", "av1", id="av1"),
+    pytest.param("h264,av1", "av1,h264", id="h264,av1"),
+    pytest.param("h264,h265,av1", "av1,h264,h265", id="h264,h265,av1"),
+    pytest.param("h264,h264,h265,h265,av1,av1,foo", "av1,h264,h265", id="duplicates+invalid"),
+])
+def test_supported_codecs(session: Streamlink, supported_codecs: str, expected: str):
+    usher_service = UsherService(session=session, supported_codecs=supported_codecs)
+    assert usher_service.supported_codecs == expected
+
+
 class TestTwitchAPIAccessToken:
     @pytest.fixture(autouse=True)
     def _client_integrity_token(self, monkeypatch: pytest.MonkeyPatch):