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Why are there no [widely supported] video formats that support transparency?

For example, the PNG image format supports transparency, allowing for some interesting effects in websites and documents. What's stopping us from having a video format that supports transparency in the same way?

saurabheights
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  • I thought video already able to do transparency (or similar effect to that) by utilising the green / blue screen background? Of course it is not a straight forward transparency as you need to edit those background and add content into it, but you achieve what you wanted... by having overlapping image? – Darius Apr 26 '14 at 06:25
  • @Darius I mean transparent display. Yes, we can use green-screen effects and whatnot to combine transparent portions of videos, but I'm talking about displaying a video with transparent background content, showing the page or document behind it. –  Apr 26 '14 at 07:30
  • You can include transparency in flash video. That's the way annoying web sites like this one do it: http://totalwebvideo.com/ – stib Apr 27 '14 at 13:39
  • @stib Oh cool I never knew that. It could be used constructively, rather than there though :P –  Apr 27 '14 at 20:13
  • That flash supports this means FLV supports it, and since the OP was asking formats, I thought it worthwhile spelling that out. – John Jun 26 '17 at 09:26

2 Answers2

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But apparently video formats do support transparency.

http://www.digitalrebellion.com/blog/posts/list_of_video_formats_supporting_alpha_channels.html

Maybe too heavy for the web?

File Format Maximum Alpha Bit-Depth
Apple Animation 8-bit
Apple ProRes 4444 16-bit
Avid Meridien Compressed 8-bit
Avid Meridien Uncompressed 8-bit
Cineon 16-bit
DPX 16-bit
Maya IFF 32-bit
OpenEXR 32-bit
PNG 16-bit
RLA 32-bit
RPF 32-bit
SGI 16-bit
SGI RAW 16-bit
Targa (TGA) 8-bit
TIFF 32-bit
Radvylf Programs
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Sambuddha
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    That article says that PNG is also a video format. A quick google search shows that this isn't true. Some of those other video formats may be accurate.. None of them widely supported. As for being too heavy for the web: We're streaming HD. That's around 20+ hd frames per second coming in. No video format is going to be too heavy for the web. The issue may lie in how widely supported the formats are.. Since none of those video formats are supported in many devices, we can't count on any of them to work in a document or web page. –  Apr 26 '14 at 07:35
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    The video codecs that support transparency are intended for post production use, and are high quality, lossless or near lossless. They run at very high bit rates compared to a delivery codec like h.264 - prores 4444 for example runs at 330Mbits per second. That's around 2.5 Gbyte for a minute. So yes, too "heavy" for the web. – stib Apr 27 '14 at 13:26
  • PNG *is* a video codec, but not a container, so you can have a quicktime mov file encoded using png compression (see http://superuser.com/questions/300897/ ) – stib Apr 27 '14 at 13:28
  • @stib Oh, I see, I didn't realize that any video ever got THAT heavy. I was very wrong in that last comment, it seems. Do you know of any attempts to optimize a web-safe video format for transparency besides flash? Flash seems like its future isnt so bright. –  Apr 27 '14 at 20:15
  • prores 4444 is comparitively lightweight compared with say, my Blackmagic camera. It shoots !6-bit raw dng image sequences at 5Mb per frame, or ~ 7.5GB / Minute. But obviously as it's a camera format there's no transparency. Different codecs do different jobs. – stib Apr 28 '14 at 02:32
  • @stib PNG is not a video codec except in the useless trivial sense. It's an image codec, and you can use *all* image codecs to encode videos, because all videos are sequences of images. Besides, said *video format* and so did the OP. So we're indeed talking containers to begin with. – John Jun 26 '17 at 09:21
  • Well, I'll agree to disagree. Given that you can encode a quicktime movie in a mov container with png codec (much loved by VJs apparently) I'd say it's a video codec, but given that it's probably creating a quciktime file containing an image sequence you could say it's not. I *could* argue that's what any all I-frame codec does, but I can't be bothered. Also I didn't realise that "format" = "container" now. To me "format" is the kinda term someone might use if they don't know the difference between codec or container, but I must be mistaken. – stib Jun 27 '17 at 13:11
  • Does MP4 also support alpha channel for pixels in it? – android developer Dec 06 '18 at 13:38
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Because there is little purpose in transparency for most people. If you are watching a video, it doesn't need transparency since your screen can't display it. If a video on a website wants to give the illusion of transparency, it can use the same background colour as the website does. Although common codecs such as MPEG-2 and h.264 don't support transparency, there are ways for those who need it such as series of images.

If we use this video as an example, it utilises an artificial green screen so people can easily import it into video editors with transparency. However, have a peak in the description and a download is available which contains each frame as a PNG as well as a lossless .mov with transparency! PNGs are 30MB, MOV is 174.1MB.
https://youtu.be/rBfMEUiobfE

spacer GIF
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  • Just putting it here kinda as a tl;dr: to use MOV with transparency, one option is to use codec Apple QuickTime Animation (`qtrle` in FFmpeg) and pixel format as `argb` or something like that. Good luck! – Sreenikethan I Nov 15 '20 at 03:54