Convert WTV to M4B — Free Online Tool
Convert WTV recorded TV files from Windows Media Center into M4B audiobook format, extracting and re-encoding the audio track to AAC inside an MPEG-4 container with chapter and bookmarking support. This is ideal for repurposing documentary, lecture, or spoken-word broadcast recordings into a portable audiobook you can listen to on any Apple or podcast-compatible device.
to
FFmpeg Command
Copy this command to run the same conversion locally with FFmpeg on your desktop. Download FFmpeg
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Note: Browser-based encoding uses approximate quality targets. For precise CRF compression, copy the FFmpeg command above and run it on your desktop.
Estimated output:
Conversion Complete!
DownloadHow It Works
WTV files are Windows Media Center DVR recordings that typically contain a video stream (often H.264) alongside one or more AAC or AC-3 audio tracks, plus broadcast metadata. Since M4B is a pure audio format, the video stream is completely discarded during this conversion — only the primary audio track is extracted and re-encoded to AAC at 128k bitrate. The output is wrapped in an MPEG-4 container with the -movflags +faststart optimization, which relocates the file's moov atom to the beginning of the file for fast playback start and streaming. Any embedded broadcast metadata from the WTV container (such as episode titles or channel info) is not automatically carried over, as M4B uses its own ID3-style tag structure.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg tool. In the browser-based version of this tool, FFmpeg.wasm (a WebAssembly port) runs this command entirely in your browser without uploading your WTV file to any server. |
-i input.wtv
|
Specifies the input file — your WTV Windows Media Center recording. FFmpeg reads the ASF-based container and identifies all available streams, including video, audio, and any embedded subtitle or metadata tracks. |
-c:a aac
|
Sets the audio codec to AAC (Advanced Audio Coding), which is the required codec for M4B files and the standard for Apple audiobook and podcast playback. Any audio in the WTV file — whether AC-3, MP2, or already-AAC — is re-encoded to AAC. |
-b:a 128k
|
Sets the AAC audio bitrate to 128 kilobits per second, a widely accepted quality level for spoken-word broadcast content such as documentaries, lectures, and news programs. You can raise this to 192k or 256k for recordings with significant music content. |
-movflags +faststart
|
Moves the MPEG-4 moov atom (the file's index and metadata) to the beginning of the output M4B file. This is essential for M4B audiobooks that will be streamed or hosted online, as podcast apps and audio players can begin playback immediately without buffering the entire file. |
output.m4b
|
Specifies the output filename with the .m4b extension. The M4B extension signals to Apple devices, iTunes, and podcast apps that this is an audiobook-type file with playback position bookmarking enabled, distinguishing it from a plain .m4a audio file. |
Common Use Cases
- Convert a recorded documentary or educational TV broadcast into an M4B audiobook to listen to during a commute without needing the video
- Repurpose a recorded lecture or talk show captured via Windows Media Center into a podcast-compatible M4B file for playback in Apple Podcasts or Overcast
- Archive the audio commentary track from a recorded sports broadcast as a bookmarkable M4B so you can resume listening after pausing
- Extract the audio from a recorded radio program that was broadcast over digital TV and saved as a WTV file, converting it to the standard audiobook format for long-term storage
- Prepare a recorded interview or panel discussion from a TV capture card into an M4B file that supports chapter markers, allowing listeners to navigate between segments
Frequently Asked Questions
No — M4B is a strictly audio-only format and cannot contain a video stream. During this conversion, the entire video track from your WTV file is dropped and only the primary audio track is extracted and re-encoded. If preserving the video is important to you, consider converting to MP4 or MKV instead.
By default, FFmpeg selects the first audio track it identifies in the WTV container, which is typically the primary broadcast language track. M4B does not support multiple audio tracks, so only one stream can be included in the output. If you need a specific audio track, you can add the -map 0:a:1 flag to the command to select the second audio stream (index 1), for example.
There is some quality loss because the audio is being re-encoded to AAC at 128k bitrate, regardless of the source audio codec in the WTV file. If the original WTV recording already used AAC, this means a second generation of lossy compression is applied. For spoken-word content like documentaries or lectures, 128k AAC is generally transparent and the quality difference is negligible. For music-heavy content, you may want to increase the bitrate to 192k or 256k.
Change the -b:a 128k value to a higher bitrate such as -b:a 192k or -b:a 256k. For example: ffmpeg -i input.wtv -c:a aac -b:a 192k -movflags +faststart output.m4b. Higher bitrates produce better audio fidelity and larger files. For most spoken-word broadcast content, 128k is sufficient, but 192k is a good choice if the original recording includes music or sound effects.
M4B supports chapters natively, but the FFmpeg command shown here does not automatically generate chapters from the WTV file because WTV does not store chapter data. To add chapters, you would need to supply a separate FFmpeg chapter metadata file using the -i chapters.txt input and -map_metadata flags. Tools like mp4chaps or chapter editing in iTunes can also add chapters to the M4B after conversion.
Yes. On Windows, you can use a batch script: for %f in (*.wtv) do ffmpeg -i "%f" -c:a aac -b:a 128k -movflags +faststart "%~nf.m4b". On Linux or macOS, use: for f in *.wtv; do ffmpeg -i "$f" -c:a aac -b:a 128k -movflags +faststart "${f%.wtv}.m4b"; done. This processes each WTV file in the current directory and outputs a correspondingly named M4B file.
Technical Notes
WTV is a proprietary Microsoft container built on the Advanced Systems Format (ASF) and used exclusively by Windows Vista/7/8/10 Media Center. It supports multiple audio tracks, subtitles, and rich broadcast metadata including program titles, channel names, and recording timestamps — none of which map cleanly to M4B's ID3-style tag system and are therefore lost in this conversion. The audio in WTV recordings varies depending on the broadcast source: North American ATSC broadcasts typically use AC-3 (Dolby Digital), while some recordings may already contain AAC. In both cases, FFmpeg re-encodes to AAC for M4B compatibility. The -movflags +faststart flag is particularly important for M4B files intended for streaming or podcast hosting, as it ensures the metadata index is at the start of the file rather than the end, allowing players to begin playback without downloading the entire file. Note that M4B files produced this way will be recognized as audiobooks by iTunes and Apple Books, and Apple devices will remember playback position automatically.