Alpha Channel in H264?

I would like to encode an alpha channel in H264 streams. I am looking for an
app that will provide that functionality. Any ideas?

 

Ken..

I would like to ENCODE alpha data in H264 streams.

Yes.. an alpha channel would have to be appplied prior to conversion. Assume
I have that covered..

So.. the question I asked was whether anyone knows of any encoders that will
accept alpha encoded data such as ANY 32 bit image format and convert it to
single bit or grayscale encoded alpha (transparency) as part of the H264
encode. My application requires a transparency channel in H264 encode. None
of my NLEs offer a solution so prior to coding our own I thought someone may
already know of an encoder which will implement this feature of H264. I
haven't thoroughly gone through the Quicktime Pro stuff yet.. the solution
may be there but we shy away from QT in any of our commercial workflow..

Of course I am not using H264 for editing source. Just curious. .. how did
you get that from my question?

For the record I am developing content for our hardware device which will
have a modified H264 decoder that will extract and use the alpha channel.

Thanks

nao

 

Ken.. I am a compositor! TV, Features.. I know what an alpha channel is..
I've been using them since their inception in targa files for what.. 20
years now..

transparency isn't a display effect. It is a method of combining two images
with proportionate, opacity determined on a per-pixel basis. It has nothing
to do with display or displays.

H264 provides for an alpha channel. Most encoders don't provide an interface
for it. I thought someone may know of a high end implementation which allows
for that part of the spec to be implemented.

I am a 3d Animator / Compositor / VFX supervisor. I know alpha compositing
inside and out. It is an essential part of every comp. But I am
implementing the alpha compositing feature in hardware and since the H264
format allows for alpha I ought to be able to create content with that in
mind. Problem is.. I don't see it in any of the encoder implementations here
in Premiere, FCP, or the other apps I normally use for post. So.. I may have
to create an app to feed an H264 encoder to provide the interface to the
alpha part of the stream.

I thought someone may be aware of a method. I think it is an appropriate
question for a desktop video forum.

But perhaps this is a matter for an alternate stream or parallel stream in
MPEG4 or H264.

Thanks though.

nap.

 

maybe there is a more standard way to do this. .. at least for my
preliminary tests with the hardware I have..

Suppose you had to create a MPEG or H264 stream with a pair of images for
each frame. How would you go about that?

I was thinking that I could write an app to prepare the frame data anyway I
want it.. for instance,

If I was working with SD res I might make a frame sequence that was
1440x480. The left half of the frame would be the color data and the right
half would be a grayscale or binary image representing the alpha channel.. I
suppose that would work fine and It would't really require any code from
me.. given that I can encode any frame size I want to.. within limits of
course.

I own DVD authoring apps like Encore and DVD Studio but I never use them..

How would you folks do that?

thanks..

nap

 

pretty much the same thing but the source is a compact data stream from
flash memory.

yes.. 'overlay streams' could be used I think.. the images I am overlaying
come from another video stream. So in the MPEG stream I need the color data
and the transparency data on a per frame basis.

I didn't see parts 11.14 or 15 in that doc.. I will look a little deeper
into the spec. . .

I wonder what apps would create those overlay streams, from my frame seqs or
quicktimes or whatever, that we can get our hands on ?


Thanks Ken!