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I have a sequence of PNG-images with transparency which I want to convert to an FLV video with transparency.

So far I have been using ffmpeg to create FLVs (vp6a), but it doesn't seem to support alpha channels.

The only software I found so far is Adobe After Effects, but it is too pricey. And then there is Adobe Flash Media Encoder, but it can only encode live from devices and not from file.

So is there an open source alternative that can create FLVs with alpha channels?

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AviDemux, open first Image via "File"->"Open", add following images via "File"->"Append...".

Choose "Sorenson Spark" in Video, "FLV" in Format. Configure your settings, play with filter, then Save as Video, and you're done!

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thanks, but it doesnt seems as if sorenson spark supports alpha channels. i would like to encode in VP6a. – clamp Aug 31 '10 at 8:36
So install/incorporate the VP6a codec and use AviDemux. – Grumpy ol' bear Aug 31 '10 at 8:40
ok, but the only version of vp6a i found is commercial. do you know of an open source/free alternative of it? – clamp Aug 31 '10 at 8:48

In a browser, you can display an FLV with alpha channel with just changing some parameters.
See the following article for an example: Alpha Video and HTML: How did they do that?

If you are looking for software to do that, I don't know of any good open-source solution, but there is a low-budget commercial alternative : Moyea Flash Video MX Pro ($99.95), with a free trial for checking it out. You can watch a demo video tutorial here.


The K-Lite Codec Pack is said in the Codec Guide to contain all the flavors of the VP6 codec : VP60, VP61, VP62, VP6A, VP6F.

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thanks, but i am looking for a free tool that can create FLVs with alpha channel (VP6a codec) – clamp Aug 31 '10 at 8:27
@clamp: Then go ahead and download VP6 from Google bought On2 Technologies and released it to the public. Actually, there are also VP7 and VP8, but I haven't looked into them. VP6 sounds good enough from the description. – harrymc Aug 31 '10 at 14:43
thanks, but i am looking for VP6a, the one that supports alpha channels. (video with transparency) – clamp Sep 1 '10 at 8:20
@clamp: See my edit. I am also not sure that the link in my comment doesn't also contain vp6a. – harrymc Sep 1 '10 at 9:34
The K-Lite Codec pack is mostly for decoding, and only does encoding to a small number of formats. I don't believe VP6a is one of those. – Simon East May 13 '11 at 5:30

I found these:

  • FLV Converter

  • FFmpeg this is supposedly an open source software

  • on2 This supposedly has a cheap version that you can purchase.

I'm not too familiar with flv so i hope this can guide you in the right direction.

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thanks, but ffmpeg is what i am using so far already, but it cannot encode in VP6 or VP6a, just h263 which doesnt support alpha. – clamp Aug 31 '10 at 8:29

VP6a encoding is pretty new and therefore only supported in commercial products like Adobe After Effects and Sorensen Squeeze.

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