HandBrake can output WebM, but the container accepts only VP8, VP9 or AV1 video and only Vorbis or Opus audio — and it cannot carry soft subtitles at all. Three lines in HandBrake's documentation, and between them they explain nearly every complaint about WebM output: why an ordinary H.264 file has to be re-encoded from scratch, why a subtitle track goes missing, and why the VP9 presets HandBrake does ship are rated "Ultra slow."
One caveat first: HandBrake marks its own containers page as a draft — "This article is a draft and may contain incomplete or incorrect information." What follows is documented behaviour, not a guarantee.
The limits, at a glance
That page describes what HandBrake produces: "HandBrake creates the widely supported container formats MKV and MP4 (sometimes seen as M4V), in addition to the WebM container format, which is subset of MKV." Three containers — and WebM is the narrowest by a wide margin:
| MP4 | MKV | WebM | |
|---|---|---|---|
| Video | H.264, H.265, MPEG-4, MPEG-2, VP9, AV1 | H.264, H.265, MPEG-4, MPEG-2, VP8, VP9, AV1, Theora, FFV1 | VP8, VP9, AV1 |
| Audio | AAC, MP3, AC3, E-AC3, TrueHD, Opus, FLAC, ALAC | AAC, MP3, AC3, E-AC3, TrueHD, Vorbis, Opus, FLAC or ALAC | Vorbis or Opus |
| Soft subtitles | Yes, text | Yes, bitmap (vobsub) or text | No — documented as currently unsupported |
| Hard-burned subtitles | Yes — 1 track only | Yes — 1 track only | Yes |
Every cell in the video and audio rows is taken verbatim from that page's per-container summaries. Two things it does not say matter as much as what it does:
- Chapters and variable frame rate. Both are stated for MP4 and for MKV. The WebM section mentions neither, either way — check the official documentation before assuming they survive.
- Lossless audio. The audio page says HandBrake "supports FLAC and ALAC (both 16 and 24bit) when the output format is MKV or MP4." WebM is not in that condition, and the container page lists only Vorbis and Opus for it.
Why there is no "just rewrap it" option
This is the part that catches people used to remuxing. Changing a container is normally cheap: you lift the existing streams out of one wrapper and drop them into another, with no re-encoding.
That path does not exist for WebM in HandBrake. H.264 is not on WebM's list, and neither is H.265 — so the video in a typical MP4 has to be re-encoded into VP8, VP9 or AV1, a full decode-and-re-encode of every frame.
Audio has the same problem. WebM stores audio "in either Vorbis or Opus formats," so an AAC track — the audio in the default Fast 1080p30 preset, and in every other General and Web preset — gets re-encoded too.
And no preset sidesteps it: HandBrake's official preset tables list only MP4 and MKV outputs. Every preset in the General, Web, Devices, Matroska, Hardware and Production groups produces one or the other.
Why it is so slow
The official presets built on VP9 are the five VP9 Matroska ones — VP9 MKV at 2160p60 4K, 1080p30, 720p30, 576p25 and 480p30. All five carry the same encoding speed rating: "Ultra slow."
That is the slowest label anywhere in HandBrake's official preset tables, and nothing else earns it. The Super HQ presets, built to produce "Very large" files at "Super high" quality, are only rated "Very slow." VP9 is a full step below them.
The codec page backs this up from the other direction. It describes VP9 as offering "Slower encoding compared to x265," and describes x265 itself as "Significantly slower than software H.264/AVC encoders."
Two more documented facts make it worse:
- No hardware encoder is listed for VP9. The codec page names hardware encoders for H.264 (Intel QuickSync, AMD VCE, Nvidia NVENC, MediaFoundation), for H.265 (the same list) and for AV1 (Intel QuickSync, Nvidia NVEnc, AMD VCN). The VP9 entry names none — it appears as VP9 (libvpx), software only. Your GPU does not rescue this encode the way it would an H.265 one.
- No recommended quality range is published for VP9. HandBrake's quality guidance gives RF ranges for x264 and x265, and a separate set for SVT-AV1. For everything else it says only: "For other encoders, start with a value in the middle of the scale, and adjust in small increments as desired." There is no official number to aim at, and the same page warns that quality values are not comparable across encoders — an x264 encode at RF 25 tells you nothing about a VP9 encode at RF 25.
So: the slowest encoder in the table, on CPU only, with no published target value to calibrate against.
What to do instead
If WebM is genuinely required — an embed target, a site that rejects MP4 — and you just need the file, you do not have to run a VP9 encode on your laptop at all.
Try it right here
Runs in your browser. Your file is not uploaded anywhere.
That runs in this browser tab: the file is read from disk, converted locally, handed back, never uploaded. Going the other direction is WebM to MP4, and MP4 to WebM is the same converter without the article around it.
If you are in HandBrake because you want a smaller file rather than specifically a WebM one, reconsider the target. H.265 is described as offering "higher quality encodes and smaller file sizes" than H.264, and AV1 — the successor to VP9 — is the one WebM-legal codec with both hardware encoders and published RF ranges. Choose the container for the codec you want, not the codec for the container.
Gotchas specific to WebM
VP8 is accepted but abandoned. WebM's codec list includes VP8, and HandBrake's deprecated-presets table shows what happened to the presets that used it: VP8 MKV 1080p30, 720p30, 576p30 and 480p30 are all listed with a replacement of "None" and the note "Obsolete. AV1 is the successor to VP9, which is the successor to VP8." If you are choosing a codec today, VP8 is not the one.
Subtitles can only be burned in. The subtitles page is unambiguous: "Soft subtitles are currently unsupported in the WebM container." That leaves hard burn, which HandBrake defines as subtitles "written on top of the image permanently." Burn-in has its own documented cap, and it is not WebM-specific: for MP4 and for MKV alike the subtitles page states "you can only burn 1 subtitle track into the video." No separate figure is published for WebM, so check the official documentation before assuming you can stack more than one. If you need captions a viewer can toggle, WebM is the wrong container and you want MKV or MP4 instead.
WebM as an input is fine. These restrictions are about output only. HandBrake's source-formats page says it "can open web videos in FLV, WEBM, MP4, and many other formats."
Preset resolutions are ceilings, not targets. If you start from a VP9 MKV preset before switching containers, remember what the names mean: higher resolution video "will be downscaled to a maximum resolution," and higher frame rates "will be peak limited to a maximum frame rate." A 480p source under a 1080p30 preset is not upscaled — more on that in why HandBrake changed my resolution.
FAQ
Can HandBrake export WebM? Yes. HandBrake's containers page lists WebM alongside MP4 and MKV as a format it creates. The limits are on what can go inside it: VP8, VP9 or AV1 video, Vorbis or Opus audio, and no soft subtitles.
Why is HandBrake WebM encoding so slow? Because the WebM-legal software codecs are slow ones. All five official VP9 presets are labelled "Ultra slow," the slowest rating in HandBrake's preset tables, and the codec page calls VP9 slower than x265, which it in turn calls significantly slower than software H.264. No hardware encoder is listed for VP9, so there is no GPU shortcut.
Can I convert MP4 to WebM in HandBrake without re-encoding? No. WebM accepts only VP8, VP9 and AV1 video, and a typical MP4 holds H.264 or H.265 — neither is on the list, so the video must be re-encoded rather than rewrapped. The same applies to AAC audio, which WebM cannot store.
Why did my subtitles disappear from the WebM file? WebM cannot hold soft subtitle tracks. HandBrake's documentation states plainly that "Soft subtitles are currently unsupported in the WebM container," leaving hard burn-in as the only route — and that writes them into the picture permanently. Note the burn-in cap the same page gives for MP4 and MKV: "you can only burn 1 subtitle track into the video."
What RF value should I use for VP9 in HandBrake? HandBrake does not publish one. Its recommended RF ranges cover x264, x265 and SVT-AV1 only; for other encoders the guidance is to start in the middle of the scale and adjust in small steps. Do not carry an x264 number over — the page is explicit that quality values are not comparable between encoders.
Is there a WebM preset in HandBrake? HandBrake's official preset tables list only MP4 and MKV outputs. The nearest thing is a VP9 MKV preset, which gets you a WebM-legal codec but not the container.
Container capabilities, preset speed ratings and codec notes cited from HandBrake's official documentation, checked 23 September 2026. HandBrake marks its containers page as a draft, so verify against the current page before relying on it. More limits explained in the limits archive; the browser-based converters are listed under all Clapr tools.
