update yt-dlp to prefer ffmpeg for vod downloads

[Zibbp]

• Prefer FFmpeg for Twitch HLS/VOD downloads to handle playlist discontinuities reliably.
• Preserve configured yt-dlp options while preventing them from overriding the application’s temporary output path.

[coderabbitai]

Walkthrough

The Twitch download path now filters configured yt-dlp arguments, centralizes argument construction, prefers FFmpeg for HLS handling, preserves the application-owned output path, and verifies argument ordering.

Changes

Twitch download argument handling

Layer / File(s)	Summary
Filter configured yt-dlp arguments internal/exec/exec.go, internal/exec/exec_test.go	Configured yt-dlp arguments are trimmed, empty values are removed, and output or path options are excluded. The test covers multiple option forms.
Centralize Twitch arguments and validate ordering internal/exec/exec.go, internal/exec/exec_test.go	A helper builds default Twitch yt-dlp arguments with MP4 output, progress, certificate, and FFmpeg-preferred HLS options. The download path uses the helper and appends configured arguments after the defaults. The test verifies FFmpeg preference and argument ordering.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 inconclusive)

Check name	Status	Explanation	Resolution
Description check	❓ Inconclusive	No pull request description was provided, so its relevance to the changeset cannot be assessed.	Add a concise description that explains the FFmpeg preference, argument filtering, and related regression tests.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly summarizes the primary change: configuring yt-dlp to prefer FFmpeg for Twitch VOD downloads.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ffmpeg-hls

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@internal/exec/exec.go`:
- Around line 76-79: Trim whitespace from each token in the configArgs loop
before appending it to args, and use the trimmed value for both the empty check
and append. Preserve skipping empty tokens while ensuring CreateCommand receives
normalized arguments.
- Around line 74-80: Update argument construction in the exec flow so
user-supplied config.Parameters.YtDlpVideo arguments cannot override
video.TmpVideoDownloadPath. Reject output-changing options, including
-o/--output and --paths (with their value forms), before appending arguments, or
otherwise ensure these options are excluded while preserving all other custom
arguments. Keep the application-owned output option authoritative.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 9c54ae4d-19b6-4a5d-96c9-857757746c8b

📥 Commits

Reviewing files that changed from the base of the PR and between 90a05a1 and f2cd508.

📒 Files selected for processing (2)

• internal/exec/exec.go
• internal/exec/exec_test.go