CAVS to VOB Converter

CAVS to VOB — Wrapping a Bare AVS Stream in a DVD Program Stream

A .cavs file is a raw Chinese AVS video bitstream — AVS1-P2, the JiZhun profile, which ffmpeg's own decoder identifies as "Chinese AVS (Audio Video Standard) (AVS1-P2, JiZhun profile)". It is picture data with nothing around it: no container, no index, no audio, no duration. A .vob is the opposite kind of thing — an MPEG-2 Program Stream, the packetised form DVD-Video discs store their content in.

The conversion is therefore a re-encode into a stream a DVD authoring tool can read. Two things need saying up front, because both catch people out: the output is silent, since a raw AVS stream never carried a sound track, and a single .vob is not a DVD, since a real disc is a folder structure rather than one file. Everything below assumes DVD authoring is why you are here, because it almost always is.

How to Convert CAVS to VOB

1. Upload Your CAVS File: Drag the .cavs onto the page or click "+ Add Files". Several raw streams can queue and run with the same settings.
2. Leave Video Codec on MPEG-2: The dropdown offers MPEG-1 and MPEG-2, with MPEG-2 pre-selected. MPEG-2 is what DVD-Video is built on; MPEG-1 will mux into the program stream but belongs to the Video CD era.
3. Choose the Audio Codec for Your Disc Standard: The list is AC3, DTS (DCA), MP2 and MP3, and it opens on MP2. That default is fine for a PAL/SECAM disc and wrong for an NTSC one — see the table below.
4. Set Video resolution and Trim, Then Convert: Video resolution opens on Keep original; DVD authoring almost always wants an explicit 720x480 or 720x576 instead. Trim opens on "Unchanged" and takes a Time Range. Click Convert. Files are uploaded over an encrypted connection, converted on our servers and deleted automatically after a few hours — no sign-up, no watermark, never shared or made public.

What DVD-Video Actually Requires

The output is a valid MPEG-2 Program Stream — we checked the bytes, and it opens with the pack-start code 00 00 01 BA, exactly as a program stream should. Whether an authoring tool or a set-top player accepts it depends on choices you make on this page:

The audio rows come from the DVD-Video specification's own requirement that a 525/60 disc must carry PCM or Dolby Digital on at least one track, while a 625/50 disc may use MPEG audio instead (DVD FAQ, audio details). Since a raw .cavs has no sound in it at all, this only matters if you intend to lay audio in afterwards — but the codec you pick here is what the file declares, so pick the one your target disc standard allows.

MPEG-2 Rate Control: What Moves the Output and What Does Not

The File Compression group shows six modes, and on MPEG-2 they do not all behave the way their names suggest. MPEG-2 has no constant-quality mode of the kind H.264 has, so the two quality modes are converted into a bitrate before the encoder runs:

• Constant Quality and Constraint Quality hand the encoder a quality number it cannot use. The value is accepted and then discarded, and the encode falls back to a minimum bitrate derived from the output resolution. Moving the slider changes nothing.
• Quality Preset, Specific file size, Constant Bitrate and Variable Bitrate all resolve to a bitrate, which MPEG-2 does understand — but each is raised to that same resolution floor if it falls below it.

The floor is worth knowing, because it is the reason a "make it small" request can come back larger than you asked:

So on this page the honest quality lever is resolution, not the quality slider. For a 720x480 encode, the floor of 2 Mbps is comfortably below what DVD-Video allows anyway — a ten-second 720x480 test encode with AC-3 audio came to 2,877,440 bytes, an overall rate of about 2.3 Mbps. If you want the slider to do something, switch Video Codec to MPEG-1, which does use a quantiser; it is not a DVD-friendly choice, but the control is real there.

The Silence Is the Source, Not the Conversion

There is no audio step on this route because there is nothing to extract. In Chinese broadcast and optical-media workflows the picture was encoded as its own AVS elementary stream and the sound travelled as a separate stream, the two being muxed together only later into a combined container. Whoever demuxed your file kept the video and discarded the rest.

The same absence explains a second oddity: a bare elementary stream carries no duration, no bitrate and no frame-rate declaration of its own, so a probe returns nothing for any of them and the demuxer falls back to an assumed rate. That is why size-targeting modes have so little to work with on this page, and another reason to reach for an explicit resolution and bitrate rather than a percentage or a preset.

If you need the soundtrack, convert the container the stream was demuxed from — the MP4, MKV or transport stream — rather than the orphaned .cavs.

Common Errors and How to Fix Them

• "The VOB is silent" — expected. The raw AVS stream had no audio. Add it in your authoring application, or go back to the container the stream came out of.
• "My authoring software will not import it" — check the frame size first. Set Width x Height to 720x480 for a 525/60 disc or 720x576 for a 625/50 one; most tools reject anything else outright or force a re-encode of their own.
• "The file is bigger than I asked for" — you hit the MPEG-2 minimum-bitrate floor for the output resolution. Reduce the resolution rather than the bitrate; that is the change that actually shrinks the file.
• "Moving the quality slider does nothing" — correct, on MPEG-2. The value is discarded and a bitrate is used instead. Use a bitrate mode, or switch to MPEG-1 if you specifically want a quantiser.
• "The upload is rejected or the decode fails" — the file may be AVS2 or AVS3 rather than AVS1. They share a family name and nothing else: our decoder covers AVS1-P2 JiZhun, and a raw AVS2 stream is a different codec entirely. Convert it from its original container instead.
• "There are comb lines through motion" — the source was interlaced broadcast material and no deinterlacing is applied anywhere in the pipeline. Deinterlace in an editor.

Frequently Asked Questions

Is the VOB I get a DVD I can burn?

Not on its own. A DVD-Video disc is a VIDEO_TS folder containing .VOB payload files alongside .IFO navigation files and .BUP backups, with the whole thing indexed so a player can find titles, chapters and menus. This page produces the payload — a valid MPEG-2 Program Stream — and nothing else. Feed it to an authoring application, which builds the folder structure and writes the navigation files around it.

Why is the output silent when my source clearly had sound?

Your source almost certainly did not. A .cavs file is a video elementary stream with no container around it, and elementary streams carry one kind of data only. If the material originally had audio, that audio was a separate stream, and it was left behind when the video was demuxed. Nothing on this page can recover it. Convert the original container instead, or lay the audio in during authoring.

Which audio codec should I pick if there is no audio anyway?

It still matters, because it is what the file declares and what an authoring tool inspects. Choose AC3 if the disc will be 525/60 (NTSC), where the specification requires PCM or Dolby Digital on at least one track. MP2 — the pre-selected value — is legal on 625/50 (PAL/SECAM) discs but not sufficient on NTSC ones. DTS is permitted as an additional track on both but never as the only one.

What is AVS1, and how is it different from AVS2 or AVS3?

AVS1 is the first generation of China's national Audio Video Standard, roughly contemporary with and comparable to H.264 in ambition. What a .cavs file normally contains is AVS1-P2 in the JiZhun profile, which is what our decoder handles. AVS2 and AVS3 are later, separate codecs in the same national programme — closer to HEVC and to AV1 respectively — and they are not backward-compatible bitstreams. A file with a .cavs extension that actually holds AVS2 will not decode here.

Why does the quality slider do nothing on MPEG-2?

Because MPEG-2 has no constant-quality mode to receive it. When you select Constant Quality or Constraint Quality on an MPEG-2 encode, the number is handed to a codec that cannot use it, so the pipeline falls back to a bitrate derived from the output resolution. The controls that do work are the bitrate ones and, above all, the resolution. Switching Video Codec to MPEG-1 gives you a genuine quantiser, but MPEG-1 is a Video CD-era choice rather than a DVD one.

What frame size should I use?

Whatever your disc standard specifies, entered explicitly. Set Width x Height to 720x480 for a 525/60 disc or 720x576 for a 625/50 one. Do not rely on the Preset Resolutions list for this: it sets the height only and lets the width follow the source's aspect ratio, which will not give you 720 across. Note also that any rescale flattens the source's pixel aspect to square, which matters because DVD frames are anamorphic — set the pixel dimensions the standard asks for and let the authoring tool declare the display aspect.

Can I convert just part of the stream?

Yes. Switch Trim from "Unchanged" and enter a Start time and Duration in seconds or as HH:MM:SS.sss. Bear in mind that a raw elementary stream has no index, so seeking into the middle of a long one means decoding up to that point — it works, but it is not instant. The Video Cutter accepts .cavs if you would rather cut visually.

Would MPEG-2 in a different container suit me better?

Possibly. If the destination is not a DVD authoring tool but simply "something that plays MPEG-2", CAVS to MPEG-2 writes the same codec into an MPEG program stream under a plainer name, which some software prefers. And if the goal is a file you can actually watch, share or edit, CAVS to MP4 is a far better destination — H.264 is smaller, sharper at the same size and understood by everything.

How long are my files kept?

Your .cavs is uploaded over an encrypted connection, decoded and re-encoded on our servers, and both it and the VOB output are deleted automatically after a few hours. Nothing is shared or made public and no account is required. Because MPEG-2 output is bulky by modern standards, expect the VOB to be considerably larger than the AVS stream you uploaded.