MultitudEnc

What is MultitudEnc?

MultitudEnc is a free app by BrainCrash soft. It was born mainly to convert multi-channel audio of video files to stereo. There are many tools for video encoding, but I didn't find one that pleased me to convert just audio... so I made my own. With this tool, you can encode the audio to stereo while leaving the video untouched. This will make the process much faster than re-encoding the whole video. The app is built with WPF and C#, and uses FFmpeg under the hood for all media processing tasks.

Why would you want to do this? (Multi channel to stereo)

Saving space (multichannel takes up more storage)
Improved compatibility (e.g. mobile viewing, streaming compatibility)
Reduced bandwidth usage
Preserving the original video quality while optimizing audio for stereo listening
Maybe you don't care about the extra channels because you're only listening on stereo equipment.

While at it I added some additional features like

Video encoding options
Partial file name replacement
Audio tracks Metadata editing
Options to remove audio tracks (like a language you don't want)

FFmpeg Setup

MultitudEnc is basically a frontend for FFmpeg. You must have FFmpeg available for the app to work. Choose one of the two methods below.

Option A System PATH Recommended

Go to ffmpeg.org/download.html
Download the latest Windows build (gyan.dev or BtbN)
Extract, you only need the bin\ folder
Open Start → "Edit the system environment variables"
Click Environment Variables, edit Path under System Variables
Add the full path to C:\ffmpeg\bin
Click OK and restart the app

Option B Portable Easyest

No PATH changes needed. Place the executables next to the app:

📁 MultitudEnc\

✓ MultitudEnc.exe

✓ ffmpeg.exe

✓ ffprobe.exe

(other app files…)

Both ffmpeg.exe and ffprobe.exe are required.

Verify FFmpeg: Open Command Prompt and run ffmpeg -version. If you see version info, you're ready.

How to Use

Add Files - Drag & Drop

Drag any number of video files (MKV, MP4, AVI, MOV…) onto the drop zone at the top of the app window. The zone highlights in amber when you hover over it. You can drop multiple files at once, each becomes its own collapsible File Card.

Duplicate files are silently ignored. Remove a single file with the ✕ button on its card, or use Clear All to start over.

Review & Select Audio Tracks

Each File Card auto-scans the file with ffprobe and lists all audio tracks. Every track is checked by default, uncheck the ones you don't need.

Track Columns

✓ Include track in output

[LANG] Language tag (ENG, SPA, FRE, UND…)

[CODEC] Source codec (AC3, DTS, EAC3…)

[BR] Bitrate or VBR

[CH] Channel layout (5.1, 7.1, 2.0…)

Track Title Field

The editable text box sets the title metadata tag written into the output stream. ENG → "English" and other common languages are auto-filled. Edit freely before encoding.

Configure Audio Options

In the Audio panel, toggle encoding and set output quality:

Encode Audio

When checked, selected tracks are re-encoded to AAC. When unchecked, all audio is stream-copied lossless.

Bitrate

Target bitrate per output track (e.g. 192k, 256k).

To Stereo

Downmixes surround sound (5.1, 7.1…) to 2-channel stereo using -ac 2. Safe for all channel layouts.

Configure Video Options

In the Video panel, choose between stream-copying (fast) or full re-encoding:

Encode Video

Uncheck to copy the video track unchanged (much faster). Check to re-encode with the settings below.

Encoder

CPU: libx264, libx265 or NVIDIA GPU: h264_nvenc, hevc_nvenc. NVENC requires an NVIDIA GPU (GTX 900+ / RTX).

Preset

CPU: ultrafast → placebo (slower = better quality). NVENC: p1 (fastest) → p7. The preset list rebuilds automatically when you switch encoder.

CRF / CQ

Quality slider. CPU: lower CRF = better (18 is near-lossless). NVENC: CQ works the same direction (20–28 typical).

VBV (optional)

VBV Maxrate and Bufsize cap peak bitrate for streaming or device compatibility (e.g. 8M / 16M). Leave blank to skip.

10-Bit

Enables 10-bit pixel format: yuv420p10le (CPU) or p010le (NVENC). Useful for HDR or high-fidelity encodes.

Set Output Filename Rules

The Output Naming panel controls how output files are named. Outputs are always saved in the same folder as the source file.

Find / Replace

String replacement on the base filename (without extension). Example: Find .BluRay → Replace with nothing to strip a release tag.

Suffix

Appended to every output filename before the extension. Use something like _stereo or _enc to avoid overwriting the source.

Warning: If the resulting output name matches the input file, the original will be overwritten. FFmpeg runs with -y. Always add a suffix when unsure.

Process & Monitor Progress

Hit PROCESS to start. Jobs run sequentially with real-time feedback:

Status Bar

Shows current filename, per-file %, and overall queue %.

Cancel

Stops after the current job. Any partially-written output file is automatically deleted to prevent corruption.

Tips & Notes

Safe Downmix

The -ac 2 flag handles all channel layouts (5.1, 7.1, mono…) safely using FFmpeg's built-in matrix mixing. Already-stereo tracks are passed through with no quality loss.

Multi-Track Files

Files with multiple audio tracks (e.g. English + Spanish) work great. Uncheck unwanted tracks, rename the ones you keep, they'll all be encoded and tagged in the output.

NVENC Notes

NVENC requires an NVIDIA GPU (GTX 900+ / RTX series). CQ controls quality like CRF. VBV fields map to -maxrate / -bufsize for NVENC, and to -x265-params / -x264-params for CPU encoders.

Nothing to Encode?

If both Encode Audio and Encode Video are disabled, PROCESS will show a warning and refuse to start. Enable at least one pass before processing.

A note on AAC audio bitrates

When re-encoding audio to AAC, the bitrate shown in tools like MediaInfo may not match the one you selected. This is not a bug in this tool. It is a known limitation of how FFmpeg's AAC encoder works: it targets the requested bitrate but operates in a variable mode internally, and the container may carry over the original stream's declared bitrate rather than the re-encoded one.

In practice, the audio quality will reflect your chosen bitrate. If accurate bitrate reporting matters for your workflow, consider using AC3 instead, which encodes in true constant bitrate mode and reports correctly in MediaInfo.