Alpha Channel in H264?
Flatulent Father Flannigan
app that will provide that functionality. Any ideas?
Ken Maltby
"Flatulent Father Flannigan" <xr...@xt8934hgf02945.com> wrote in message
news:mqdrl.21542$Ws1...@nlpi064.nbdc.sbc.com...
>I would like to encode an alpha channel in H264 streams. I am looking for
>an app that will provide that functionality. Any ideas?
>
>
Is this an SD survailance application? There are hardware overlay
functions that take care of that.
You need to be supplying a great deal more specific data in your
posts.
I know of no situation where H.264 is being used for editing
source, except under duress. An alpha channel effect would
have been applied prior to a conversion to H.264.
You need to explain how your case is otherwise.
Luck;
Ken
Flatulent Father Flannigan
"Ken Maltby" <kma...@sbcglobal.net> wrote in message
news:aaCdnZ69XfngXjDU...@giganews.com...
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 Maltby
Hmm.... Alpha Channel aside, Transparency is a display effect,
you can use transparency when you overlay an image or video
over another image or video so that any portion of the top image
that can be identified as transparent will allow the image or video
below to show through. The "Alpha" or intensity channel provides
for ident of that "transparent" portion of the top image or video to
the display processor so that the amount of transparency of those
portions can be applied and or adjusted.
I guess I just don't see how (or why) you would expect to be
creating such a thing, as something embeded in the encode, at
the point of encoding the video or as a componet of the encoded
video, separate from the initial production/editing of the video.
For most normal people "Alpha Channel" and "Transparancy"
are delt with as effects applyed during editing. They are used
for clips of takes that are used with other clips in the construction
of a scene or effect. Then there is the actual charter of this NG.
Perhaps this is a question for another newsgroup/forum.
Luck;
Ken
Flatulent Father Flannigan
> Hmm.... Alpha Channel aside, Transparency is a display effect,
> you can use transparency when you overlay an image or video
> over another image or video so that any portion of the top image
> that can be identified as transparent will allow the image or video
> below to show through. The "Alpha" or intensity channel provides
> for ident of that "transparent" portion of the top image or video to
> the display processor so that the amount of transparency of those
> portions can be applied and or adjusted.
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.
>
> I guess I just don't see how (or why) you would expect to be
> creating such a thing, as something embeded in the encode, at
> the point of encoding the video or as a componet of the encoded
> video, separate from the initial production/editing of the video.
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.
>
> For most normal people "Alpha Channel" and "Transparancy"
> are delt with as effects applyed during editing. They are used
> for clips of takes that are used with other clips in the construction
> of a scene or effect. Then there is the actual charter of this NG.
>
> Perhaps this is a question for another newsgroup/forum.
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.
>
> Luck;
> Ken
>
>
>
Flatulent Father Flannigan
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
Ken Maltby
If you are "implementing the alpha compositing feature
in hardware" of video then I can't see how it could be
anything other than "a matter for an alternate stream or
parallel stream". What you seem to be talking about
was a common feature for broadcast mixing boards.
The MPEG4 container format specification includes
overlay stream(s) for use with H.264, perhaps that
would be a way to approach this.
http://www.digitalpreservation.gov/formats/fdd/fdd000155.shtml
Parts 11, 14 and 15 mostly.
Luck;
Ken
Flatulent Father Flannigan
"Ken Maltby" <kma...@sbcglobal.net> wrote in message
> If you are "implementing the alpha compositing feature
> in hardware" of video then I can't see how it could be
> anything other than "a matter for an alternate stream or
> parallel stream". What you seem to be talking about
> was a common feature for broadcast mixing boards.
pretty much the same thing but the source is a compact data stream from
flash memory.
>
> The MPEG4 container format specification includes
> overlay stream(s) for use with H.264, perhaps that
> would be a way to approach this.
>
> http://www.digitalpreservation.gov/formats/fdd/fdd000155.shtml
>
> Parts 11, 14 and 15 mostly.
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!
>
> Luck;
> Ken
>
>
Ken Maltby
I find for quick scratchpad type efforts, GraphEdit lets you
mess with the streams and the property pages of the codec
and other tools that are commonly available. You might
like Graphstudio, better, they are much the same.
Luck;
Ken
Ken Maltby
http://www.download32.com/directshow-overlay-filter-d60266.html
That's listed as a free one, but look at the prices for those listed below
that one.
You might be interested in what you get with a Google search
of "directshow video filters alpha channel"
Luck;
Ken