Video Encoder Utility

Overview

jelly_coder scans a folder for supported videos (.mkv, .mp4, .wmv, .mwv, .avi, .webm) and re-encodes them with size-aware defaults. It keeps subtitles/metadata, flips containers when MP4 constraints are violated, and preserves a mirrored directory tree when you choose not to overwrite in place.

Key capabilities:

• Automatic encoder selection with hardware-first preference (NVENC → QSV → AMF → x264) and explicit backend override flags.
• Height presets (auto, 1080p, 720p, 480p, 360p) with bitrate scaling so smaller outputs also shrink file size.
• Smart audio handling: copies compatible streams, forces stereo when sources are mono or pseudo-mono (e.g., WMV files with only one active channel), and warns about downmixing.
• Hardware fallbacks: if a chosen hardware encoder fails to create a session, the tool transparently repeats the job with libx264 so the batch continues.

Prerequisites

• Windows PowerShell 5.1 (default shell for the repo scripts).
• Python 3.11+ with virtual environment support.
• ffmpeg and ffprobe in PATH.
  • Hardware backends require vendor drivers and an ffmpeg build with NVENC/QSV/AMF enabled.

Installation

python -m venv .venv
.\.venv\Scripts\Activate.ps1
pip install --upgrade pip
pip install -e .

Usage

# Show CLI help
python -m jelly_coder --help

# Reduce a folder, mirror outputs under ./output/<dir>, auto-select backend
python -m jelly_coder D:\media --quality 720p

# Force Intel QSV, enable overwrite, run at debug verbosity
python -m jelly_coder D:\media --backend qsv --overwrite --log-level debug

# Change the display aspect ratio to 16:9
python -m jelly_coder D:\media --aspect 16:9

# Legacy wrapper remains available
python encode_videos.py D:\media

Key Flags

• PATH (positional): Directory scanned recursively for supported video extensions.
• --backend BACKEND: auto (default), nvenc, x264, qsv, or amf.
• --codec CODEC: Hint h264 or hevc; respected when the backend supports it.
• --quality PRESET: Downscale preset (auto, 1080p, 720p, 480p, 360p).
• --aspect W:H: Set the output display aspect ratio (e.g. 16:9, 4:3).
• --max-workers N: Concurrent encodes (default 1; hardware encoders generally behave best at 1).
• --overwrite: Replace sources in place. When omitted, outputs land in ./output/<input-folder>.
• --output PATH: Custom output directory root when not overwriting.
• --log-level LEVEL: info (default), debug, warning, etc.

Output Behavior

• MP4 targets convert SubRip/ASS to mov_text automatically; incompatible streams trigger a fallback to MKV.
• Attached artwork, metadata, and subtitle tracks are propagated.
• When the output is larger than the input, a warning is emitted so you can review or delete the file.
• Audio streams are copied when safe; otherwise they are re-encoded to AAC 192k stereo, duplicating the dominant channel if the source is effectively mono.

Encoder Backends

• Auto: Queries ffmpeg encoders and picks the best available hardware backend (NVENC → QSV → AMF → x264).
• NVENC/QSV/AMF: Uses vendor hardware. Hardware decode fallbacks are attempted before giving up.
• x264: Software-only; always available.
• If a hardware backend exhausts its attempts (e.g., Error creating a MFX session: -9 on QSV), the utility logs a warning and re-runs the encode with libx264 automatically.

Audio Handling

• ffprobe insights drive copy-or-transcode decisions.
• WMV inputs and other stereo tracks with severe channel imbalance trigger a sampling step; if only one channel has meaningful signal, the tool duplicates it so the result plays on both speakers.
• Mono and surround sources are converted to stereo with informative log messages about the change.

Development

• Run python -m pytest and flake8 before committing; coverage is enforced at 100%.
• python -m jelly_coder --help verifies CLI wiring after refactors.
• VS Code launchers in .vscode/launch.json provide ready-to-run debug sessions.

Troubleshooting

• Validate ffmpeg exposes the expected encoders: ffmpeg -hide_banner -encoders | Select-String nvenc.
• Hardware backends may need up-to-date GPU/Media drivers; keep Windows and vendor packages current.
• Delete partial outputs in output/ if you want to re-run without --overwrite.