Convert VOB to CAVS — Free Online Tool
Convert VOB files from DVD-Video discs into CAVS format, transcoding the MPEG-2 video stream to H.264 (libx264) and the AC-3 audio to AAC. This is useful for repurposing DVD content into a more compressed, broadcast-oriented container aligned with Chinese digital media standards.
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FFmpeg Command
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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
VOB files contain multiplexed MPEG-2 video and AC-3 (Dolby Digital) audio as used on DVD-Video discs. During this conversion, FFmpeg fully decodes the MPEG-2 video stream and re-encodes it using the libx264 encoder, applying H.264 compression at CRF 23 — a visually efficient quality level that significantly reduces file size compared to MPEG-2. The AC-3 audio track is simultaneously decoded and re-encoded as AAC at 128k bitrate. Because CAVS does not support subtitle streams, DVD subtitle tracks (typically stored as bitmap-based VOB subtitles) are dropped entirely. Multiple audio tracks present in the VOB are also reduced to a single AAC stream. The result is a self-contained CAVS file with modern video compression but without the DVD-specific extras.
What Each Flag Does
| Flag | What it does |
|---|---|
ffmpeg
|
Invokes the FFmpeg binary, the open-source multimedia processing engine that handles all demuxing, decoding, encoding, and muxing for this VOB-to-CAVS conversion. |
-i input.vob
|
Specifies the input VOB file. FFmpeg automatically detects the MPEG-2 program stream container, identifies the MPEG-2 video track and AC-3 audio track, and also reads any VOBSUB subtitle streams and navigation packets present in the DVD VOB structure. |
-c:v libx264
|
Instructs FFmpeg to re-encode the MPEG-2 video stream using the libx264 H.264 encoder. This is required because MPEG-2 is not a valid video codec for the CAVS container, so a full decode-and-reencode of every frame takes place. |
-c:a aac
|
Transcodes the AC-3 Dolby Digital audio from the VOB into AAC using FFmpeg's built-in AAC encoder. AAC is the only audio codec supported in this CAVS output, so the AC-3 surround audio must be fully decoded and re-encoded rather than stream-copied. |
-crf 23
|
Sets the Constant Rate Factor for libx264 to 23, which is the default quality level. For typical DVD-quality MPEG-2 sources this produces H.264 output that is visually close to the original while delivering a substantially smaller file size than the source VOB. |
-b:a 128k
|
Sets the AAC audio bitrate to 128 kilobits per second. This is adequate for stereo audio derived from DVD AC-3 tracks and balances quality against file size; increase to 192k or 256k if the source has dense surround content being downmixed. |
output.cavs
|
Defines the output filename and tells FFmpeg to wrap the H.264 video and AAC audio into a CAVS container. The .cavs extension triggers FFmpeg's CAVS muxer, which structures the output according to the Chinese Audio Video Standard container format. |
Common Use Cases
- Preparing DVD-ripped VOB content for distribution or archiving within Chinese broadcasting or media pipelines that require CAVS-compatible files.
- Reducing the large file sizes of MPEG-2-encoded VOB files for storage, since H.264 at CRF 23 can deliver comparable visual quality at roughly half the bitrate of typical DVD MPEG-2 streams.
- Converting personal DVD library rips into a more compressed format for devices or software that support CAVS playback but struggle with raw VOB MPEG-2.
- Re-encoding VOB footage from older DVD camcorders or authoring projects into a modern codec for use in video editing timelines that accept CAVS/H.264.
- Stripping the multi-track audio, menu data, and subtitle complexity out of a VOB file to produce a clean single-stream video file for simple playback or review.
- Transcoding DVD training or instructional content originally authored as VOB into a leaner format for upload or sharing on platforms with CAVS format support.
Frequently Asked Questions
Yes, this is a lossy-to-lossy transcode, so some generational quality loss is unavoidable. However, H.264 encoded by libx264 at CRF 23 is generally considered visually transparent for most DVD-quality MPEG-2 sources, which typically run at 4–8 Mbps. In practice, the CAVS output often looks comparable to the VOB source at a significantly smaller file size, so the perceptible quality difference is minimal for standard-definition DVD content.
The AC-3 audio track is fully decoded and re-encoded as AAC at 128k bitrate. AAC at 128k is efficient and suitable for stereo content, but if your VOB contains a 5.1 surround AC-3 track, the channel layout will be preserved during encoding only if FFmpeg's AAC encoder handles the downmix correctly — you may want to explicitly add '-ac 2' to the command if you intend stereo output. The Dolby Digital surround metadata and any secondary audio tracks present in the VOB are discarded.
No. CAVS does not support subtitle streams, so all subtitle tracks — including the bitmap-based VOB subtitle streams (VOBSUB) common on DVDs — are dropped during conversion. If you need subtitles, you would need to either burn them into the video stream using FFmpeg's subtitles filter before outputting to CAVS, or export them separately as an SRT or SUP file in a prior step.
FFmpeg can concatenate multiple VOB files from the same title using its concat demuxer or by using the DVD virtual filesystem. The simplest approach is to concatenate them on the command line: 'ffmpeg -i "concat:VTS_01_1.VOB|VTS_01_2.VOB|VTS_01_3.VOB" -c:v libx264 -c:a aac -crf 23 -b:a 128k output.cavs'. Alternatively, tools like MakeMKV can first merge the VOB title into a single file, which you then pass to this conversion. Processing the full disc at once avoids chapter-boundary glitches that can appear when converting individual VOB segments.
The '-crf 23' flag controls H.264 quality using Constant Rate Factor. Lower values mean higher quality and larger files — CRF 18 is often considered visually lossless for most sources, while CRF 28 gives smaller files with more visible compression. For archiving DVD content you care about, CRF 18–20 is a safer choice. For casual viewing or space-constrained situations, CRF 26–28 is acceptable. The valid range for libx264 is 0 (lossless) to 51 (worst quality).
The .cavs extension signals that the file conforms to the Chinese Audio Video Standard, a national broadcasting format developed in China as an alternative to H.264/AVC. In practice, the video stream inside is encoded with libx264 (standard H.264), so VLC, FFmpeg, and most modern media players on Windows, macOS, and Linux can play the file. However, niche or embedded devices that expect strict CAVS-specific codec compliance (AVS1/AVS2) may not recognize the container or codec, as the file uses H.264 rather than a native AVS codec.
Technical Notes
VOB files are tightly coupled to the DVD-Video specification: they carry MPEG-2 video (typically 720x480 for NTSC or 720x576 for PAL) at variable bitrates up to 9.8 Mbps, along with AC-3, DTS, or LPCM audio, bitmap-based VOBSUB subtitles, and navigation packets (NAV packs) interspersed in the stream. FFmpeg handles VOB demuxing well but the '-f vob' flag may be needed to force correct format detection when the file lacks the standard extension or comes from a renamed rip. The libx264 encoder used here does not produce native AVS (Chinese Audio Video Standard) bitstream — CAVS in FFmpeg's context uses libx264 as its video backend, so the output is H.264 video inside a CAVS container rather than true AVS1-encoded video. Metadata such as DVD title, chapter markers, and disc region information is not preserved in the output. The pixel aspect ratio (DAR/SAR) flags embedded in the MPEG-2 stream for anamorphic widescreen DVDs should be respected by libx264 automatically, but you may want to verify the output aspect ratio if the source is a non-standard anamorphic encode. Files over 1GB should be processed using the desktop FFmpeg command shown on this page, as browser-based WebAssembly processing has memory constraints for very large VOB files.