Codec which support also Alpha-Channel

[krieger2005]

I'm searching for a codec which support Alpha-Channel. I know, there are some out there, Logarith, Huffyuv....

The Problem is that those are all lossless Codecs. I don't need a lossless codec since for me the quality of, for example MJPEG with Quantizer of 1 or 2 (from FFDShow) give good results while the filesize is smaller. In the past a have done two clips, one of the clip it self and another on of the alpha-channel. But then you must bring them every time you need the clip together.

So my general Question is, is there a codec which support Alpha-Channel-Processing while does not return such big Filesizes. Stay in RGB-Colorspace is not necessary (but i don't think there is no codec in YUV-Colorspace with Alpha-Channel-Support).

[communist]

Non that I'm aware of.. but you could try PNG image series ;)

[mpucoder]

There are a number of MJPEG + Alpha codecs, try Google (http://www.google.com/search?hl=en&q=%2Bmjpeg+%2Balpha), This site (http://www.free-codecs.com/download/ACE_Mega_CoDecS_Pack.htm) looks interesting

[krieger2005]

Thanks for your answers. For PNG image series i don't think thus could give you smaller sized videos that Logarith gives. But i have not tried it yet.

For MJPEG (thanks for that hint. i never know of a hybrid MJPEG-Codec) : I have read somewhere that there are differences in quality, even with Quanticizer of 1, for different MJPEG Codecs. Since those MJPEG Codec are rare used (and not tested for the quality-loss) i'm affraid in loss of to much quality.

How about an MPEG4-Format? In the past i don't used them for HQ-Backups because the blacks looked often littlebit greenish. Does something change here?

[unmei]

You probably would not want a lossy alpha channel. Since if the alpha is a bit off, you will have dirt of "undefined color" in areas that are possibly way off the actual content region. Unless the alpha compression takes care to have all completely opaque and all completely transparent alpha values really lossless and only code the alpha value lossy if it is somewhere in-between. And no, i don't know a codec that does this.

[krieger2005]

@unmei: You are right. I have compressed before some clips with MJPEG and don't saw such Problems... However, i get the chance to try Quicktime Pro. There are two Compression-Methods which i found good: H264 and JPEG2000. The JPEG2000 one support also Alpha-Channel and give nice results.

The results a littlebit smoother than the uncompressed source. I will try some other filters since i don't own Quicktime Pro...

Maybe someone else have an other idea? Has anybody experinces in using H264-Codec of Quicktime?

[HyperHacker]

You probably would not want a lossy alpha channel. Since if the alpha is a bit off, you will have dirt of "undefined color" in areas that are possibly way off the actual content region. Unless the alpha compression takes care to have all completely opaque and all completely transparent alpha values really lossless and only code the alpha value lossy if it is somewhere in-between. And no, i don't know a codec that does this.
Or even just use lossless alpha, but with only maybe 3 bits of it.

[krieger2005]

Or even just use lossless alpha, but with only maybe 3 bits of it.

This is not a option for me. I decided now to use the two-file technique (one file for the video, the second one for the alpha-channel) since there seems nothing out what have a good compression-ration and support also alpha-channel.

Artifacts on alpha-channel are too small at thus quality-settings i use. So i don't see here a problem.

I think now about which compresser i should take. The files should exist for future editing. So when i compress it now it will be compressed after using in the editing software again. Thus it should stay in good quality.

Since AVC gives atm the best compression-ratios i think to use it. I made some test-files compressing with x264 (-> mp4) (before with the internal H264-Codec of ffdshow -> avi) with following settings: 1-pass, quantizer: with quant=13 for normal video and quant=9 for alpha-channel.

The results looks good but since i have no expirince with h.264 i would like to hear what you all think. Is this ok, what settings whould you use or wouldn't you use h.264 for archivate of videos. What codec then?

[foxyshadis]

If you don't have a lot of noise you need to keep, want to maximize your lossy quality-to-compression ratio, and don't mind slower decoding and having to use mp4 editing tools later, then avc is a great choice. I would advise against attempting to edit it in any way in avi, you'd be better off rewriting it to a b-frameless xvid or lossless format beforehand. Whatever the merits of avc-in-avi for viewing, it simply is not suitible for non-linear-editing with b-frames, and probably too slow for comfortable use. (Thus xvid or lossless.)

[krieger2005]

Thank you foxyshadis and all the others who helped me.