fix: yt-dlp im temporären Verzeichnis ausführen (Streudatei „3“)

yt-dlp ruft zur Prüfung „ffmpeg -bsfs“ auf; das System-ffmpeg 6.1.1
(Ubuntu) legt dabei eine leere Datei „3“ im Arbeitsverzeichnis an.
yt-dlp läuft jetzt in einem temporären Verzeichnis mit absolutem
Zielpfad, die Datei verschwindet mit dem Verzeichnis.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/conftest.py

@@ -12,13 +12,15 @@ def fake_yt_dlp():
     """Factory for a subprocess.run stand-in.
 
     It answers the info request with `info` and writes `vtt` where yt-dlp would
-    write the subtitle file. `run.calls` records every command.
+    write the subtitle file. `run.calls` records every command, `run.cwds` the
+    working directories.
     """
     def make(info, vtt="WEBVTT\n", write=True, fail_download=False):
-        calls = []
+        calls, cwds = [], []
 
-        def run(command, capture_output, text):
+        def run(command, capture_output, text, cwd=None):
             calls.append(command)
+            cwds.append(cwd)
             if "--dump-single-json" in command:
                 return subprocess.CompletedProcess(command, 0, json.dumps(info), "")
             if fail_download:
@@ -32,6 +34,7 @@ def fake_yt_dlp():
             return subprocess.CompletedProcess(command, 0, "", "")
 
         run.calls = calls
+        run.cwds = cwds
         return run
 
     return make

tests/test_yt_untertitel.py

@@ -1,6 +1,7 @@
 """Tests for yt_untertitel.py; yt-dlp is always replaced by fakes (no network)."""
 import subprocess
 import sys
+from pathlib import Path
 
 import pytest
 
@@ -67,6 +68,19 @@ def test_main_downloads_auto_original(fake_yt_dlp, tmp_path, monkeypatch, capsys
     assert "vtt2txt.py -i" in out
 
 
+def test_yt_dlp_runs_in_temporary_directory(fake_yt_dlp, tmp_path, monkeypatch):
+    # ffmpeg -bsfs, called by yt-dlp, leaves a file "3" in its working directory
+    run = fake_yt_dlp(AUTO_ONLY)
+    monkeypatch.setattr(yt.subprocess, "run", run)
+    monkeypatch.chdir(tmp_path)
+    run_main(monkeypatch, "-u", URL, "-n", "Rede")
+
+    assert all(cwd is not None and Path(cwd) != tmp_path for cwd in run.cwds)
+    template = run.calls[1][run.calls[1].index("-o") + 1]
+    assert template == f"{tmp_path / 'Rede'}.%(ext)s"
+    assert (tmp_path / "Rede.de-orig.vtt").is_file()
+
+
 def test_main_prefers_manual_and_defaults_to_video_id(fake_yt_dlp, tmp_path, monkeypatch):
     info = dict(AUTO_ONLY, subtitles={"de": []})
     run = fake_yt_dlp(info)
@@ -84,7 +98,7 @@ def test_main_no_matching_track(fake_yt_dlp, tmp_path, monkeypatch):
 
 
 def test_main_info_error(tmp_path, monkeypatch):
-    def run(command, capture_output, text):
+    def run(command, capture_output, text, cwd=None):
         return subprocess.CompletedProcess(command, 1, "", "ERROR: Video unavailable")
 
     monkeypatch.setattr(yt.subprocess, "run", run)

yt_untertitel.py

@@ -6,16 +6,26 @@ import argparse
 import json
 import shutil
 import subprocess
+import tempfile
 
 YT_DLP = "yt-dlp"
 
 
+def run_yt_dlp(arguments):
+    """Run yt-dlp in a temporary working directory.
+
+    yt-dlp calls "ffmpeg -bsfs" to check ffmpeg; some ffmpeg builds (Ubuntu
+    6.1.1) then leave an empty file "3" in the working directory.
+    """
+    with tempfile.TemporaryDirectory() as tmp:
+        return subprocess.run(
+            [YT_DLP, *arguments], capture_output=True, text=True, cwd=tmp
+        )
+
+
 def fetch_info(url):
     """Return the video metadata from yt-dlp, without downloading anything."""
-    result = subprocess.run(
-        [YT_DLP, "--dump-single-json", "--skip-download", "--no-playlist", url],
-        capture_output=True, text=True,
-    )
+    result = run_yt_dlp(["--dump-single-json", "--skip-download", "--no-playlist", url])
     if result.returncode != 0:
         raise SystemExit(f"yt-dlp konnte das Video nicht abrufen:\n{result.stderr.strip()}")
     return json.loads(result.stdout)
@@ -70,14 +80,14 @@ def no_track_message(info, lang):
 
 def download(url, track, is_auto, target_base):
     """Download one subtitle track; yt-dlp writes <target_base>.<track>.vtt."""
-    command = [
-        YT_DLP, "--skip-download", "--no-playlist", "--force-overwrites",
+    result = run_yt_dlp([
+        "--skip-download", "--no-playlist", "--force-overwrites",
         "--write-auto-subs" if is_auto else "--write-subs",
         "--sub-langs", track, "--sub-format", "vtt",
-        "-o", f"{target_base}.%(ext)s",
+        # Absolute, because yt-dlp runs in a temporary directory
+        "-o", f"{Path(target_base).resolve()}.%(ext)s",
         url,
-    ]
-    result = subprocess.run(command, capture_output=True, text=True)
+    ])
     if result.returncode != 0:
         raise SystemExit(f"Download fehlgeschlagen:\n{result.stderr.strip()}")