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Transparent MP4 and HEVC With Alpha: What Actually Works

By the Charmotion team · Updated

Cover illustration for the guide: Transparent MP4 and HEVC With Alpha: What Actually Works, with Charmotion demo characters

A standard H.264 MP4 can't be transparent, because H.264 has no alpha channel. Transparent video needs a codec that stores alpha: HEVC with alpha (usually in a .mov) for Safari and Apple devices, VP9 WebM for Chrome, Edge and Firefox, or ProRes 4444 for editing. On a Mac, Apple's avconvert turns a ProRes 4444 master into HEVC with alpha.

Key takeaways

  • H.264 MP4 has no alpha; "transparent MP4" usually means HEVC with alpha, or a stacked color-plus-alpha MP4 that needs a special player.
  • Export ProRes 4444 or a PNG sequence from After Effects or Premiere as the transparent master.
  • On macOS, avconvert with an HEVC WithAlpha preset made a working HEVC alpha file in our test; ffmpeg's VideoToolbox output did not open in AVFoundation.
  • ffmpeg 7.1.1 decodes HEVC alpha files without their alpha, so go through ProRes 4444 to make a WebM.
  • On iPhone, transparent regions have been reported to brighten what's behind them; check color tags and test on a device.

Can an MP4 have an alpha channel?

Not with H.264, which is what almost every "MP4" is. H.264 stores color only, so any transparent area becomes a solid color on export.

There are three things people mean by a transparent MP4:

  • HEVC with alpha. Apple's H.265 variant carries a second, alpha layer. Apple introduced playback in iOS 13 and macOS Catalina (WWDC19 session 506). Files are usually QuickTime .mov tagged hvc1.
  • A stacked MP4. Color and a grayscale alpha mask are packed side by side or top and bottom in a normal H.264 frame, and a custom player (a shader, a canvas script or an Android view) recombines them. Masko, for example, lists a "stacked MP4" for Android. It is not transparent in a plain video player.
  • A mislabeled file. Some tools say "transparent MP4" and write a WebM or MOV. Check the codec, not the extension.

For the web, the reliable recipe is two files in one <video> element: HEVC alpha first for Safari, VP9 WebM second for everyone else. The markup is in transparent video on websites.

Why won't After Effects or Media Encoder export a transparent MP4?

Because the format can't hold it. The accepted answer in Adobe's community thread on the question is blunt: "The MP4 file format does not support an Alpha Channel." Other replies note that HEVC can, but that Adobe's own exporters don't write HEVC with alpha.

The alternatives suggested in that thread are what professionals use as a transparent master:

  • QuickTime with ProRes 4444, the usual editing master with alpha.
  • QuickTime Animation or PNG codecs, larger but lossless.
  • A PNG image sequence, one file per frame.
  • VP9 WebM through a third-party exporter or ffmpeg.

Export the master once with "RGB + Alpha" channels, then make the web files from it. Never deliver ProRes 4444 to a web page: it is an editing format and far too large.

How do I make HEVC with alpha (with or without a Mac)?

On a Mac, the dependable route in our October 2026 tests was Apple's own encoder. First make a ProRes 4444 master if you don't have one (here from a transparent WebM), then convert it with avconvert, which ships with macOS and has HEVC presets "WithAlpha":

ffmpeg -c:v libvpx-vp9 -i character.webm -c:v prores_ks -profile:v 4444 -pix_fmt yuva444p10le -an master.mov
avconvert -s master.mov -p PresetHEVCHighestQualityWithAlpha -o character-hevc.mov

Reading the result back through AVFoundation showed 77% transparent pixels, matching the source. Compressor and AVFoundation's AVAssetWriter (codec hevcWithAlpha) use the same system encoder.

A common alternative is ffmpeg's hevc_videotoolbox encoder with -alpha_quality and -tag:v hvc1. In our test with ffmpeg 7.1.1 the files it wrote were larger than the opaque version, suggesting an alpha layer, but AVFoundation refused to open them (error -11801 / -12713). Test any ffmpeg-made HEVC file in Safari before you ship it.

Without a Mac, options are thinner. FFmpeg 8.0's changelog adds "libx265 alpha layer encoding," which can produce HEVC with an alpha layer on Windows and Linux; we have not verified that Safari plays its output, so test on an iPhone before relying on it. Otherwise, encode on a Mac (a cloud Mac works) or use a tool that delivers the MOV for you.

Can I play HEVC with alpha on Windows?

You can usually play the video, but don't expect to see the transparency. Windows plays HEVC only with Microsoft's paid HEVC Video Extensions (US$0.99 in the US Store listing in October 2026) or a player that bundles its own decoder. Chrome and Firefox on Windows don't render HEVC alpha as transparent, which is why the web recipe pairs it with a WebM.

To check what a file really contains without a Mac, open it in our free Transparent Video Checker, which reads the file's alpha flags and tests decoding in your browser. To preview the transparency on Windows, make a WebM from it (next section).

How do I convert a MOV with alpha to WebM?

It depends on the codec inside the MOV.

ProRes 4444 MOV: ffmpeg reads its alpha directly.

ffmpeg -i master.mov -c:v libvpx-vp9 -pix_fmt yuva420p -b:v 0 -crf 30 -an character.webm

HEVC alpha MOV: ffmpeg 7.1.1 decodes only the color layer. In our test, frames decoded from a verified HEVC alpha file had 0% transparent pixels, and ffprobe reported yuv420p. Convert to ProRes 4444 with Apple's decoder first, then encode the WebM:

avconvert -s character-hevc.mov -p PresetAppleProRes4444LPCM -o prores.mov
ffmpeg -i prores.mov -c:v libvpx-vp9 -pix_fmt yuva420p -b:v 0 -crf 30 -an character.webm

That route produced a WebM with alpha_mode=1 and 76% transparent pixels. The yuva420p pixel format is what keeps alpha in the WebM; without it, libvpx-vp9 writes an opaque file. When you later decode that WebM with ffmpeg, put -c:v libvpx-vp9 before -i, or the alpha disappears again.

Why does my transparent video look washed out on iPhone?

It's a reported, unresolved issue rather than a documented behavior. In an Apple Developer Forums thread from October 2024, a developer wrote that on iPhone and iPad "the transparent parts of the video act almost like an 'overlay', making everything behind it a lot brighter," and that the effect got worse at lower screen brightness. The same files looked right on Mac, Windows and Android.

The only Apple reply asked which color space the file used and pointed to Safari's Web Inspector, where the Media panel of a selected <video> shows the color information Safari parsed. No fix was confirmed in the thread.

What to do in practice:

  • Export with explicit, standard color tags (BT.709 for SDR) and compare them with what Web Inspector reports.
  • Test on a real iPhone at low and high brightness, over your actual page background.
  • If a small character must look exact, consider drawing it live instead: a Rive or Lottie file renders on a transparent canvas with no video compositing.

Can I skip the encoding steps?

If you start from a character, mascot or logo image, yes. Charmotion's paid plans (from $20/month) deliver each animation as both a VP9-alpha WebM and an HEVC-alpha MOV at 1080×1080, encoded with Apple's AVFoundation, so the files already pair correctly in a <video> element.

Frequently asked questions

Is a stacked MP4 the same as a transparent MP4?

No. A stacked MP4 is an ordinary opaque H.264 video with the color image and a black-and-white alpha mask packed into one frame. It looks transparent only in a player that recombines the two halves, such as a custom shader or Android view. In a normal player you see both halves.

Why does ffprobe show yuv420p for my HEVC alpha video?

Because ffmpeg reads only the base color layer of Apple's HEVC with alpha; the alpha is stored as a separate layer. In our test with ffmpeg 7.1.1, decoded frames had no transparency at all. Check the file in Safari or AVFoundation instead, or convert it to ProRes 4444 with avconvert first.

Can I make HEVC with alpha in Premiere Pro?

Not directly, according to replies in Adobe's community forum. Export ProRes 4444 with alpha from Premiere or After Effects, then convert it to HEVC with alpha on a Mac with avconvert, Compressor or AVFoundation.

Quick answers from this guide

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