best way to create video from html5 animation

问题:

I wanted to make a short intro for a video podcast. Being a geeky web developer and not already having access to or knowledge of animation tools, I thought I might take a stab at doing the intro using various html5 techniques. The problem is, how do I turn that into a video clip I can easily drop into iMovie?

If I have to, I think this can be accomplished if I only use canvas by exporting a png every frame using getImageData. The only drawback is that I'm limited to just canvas. I was hoping to use the whole range of new html5/css3/svg techniques. I don't need this functionality to work for general web use, just for myself, so I'd be happy for anything that requires installation etc. to make it work.

If I have to, I guess I can probably use a video screen capture tool, but I was hoping for a complete open source chain.

In the end, I expect I'll be creating a series of pngs and using ffmpeg to put them together, I was just hoping to figure out a great way of doing this in an automated, open source way.

Update I just wanted to clarify that what I'm basically trying to do is use HTML5 instead of something like flash, but I'm not trying to serve it to other people on the internet, I want to convert it to video, and it never needs to leave my computer, which is actually a mac, not a Linux server. If flash can do it, why not html, right? That seems to be what people are trying to claim. The problem is, I can take a SWF and convert it to standard video, but how do you do that with javascript or CSS3 animations? Obviously a screen capture tool can sort of do the job, but those are usually low frame rate, and can't be run programmatically to my knowledge.

The closest sort of thing I can think of that isn't a screenshot tool would be something like webkit2png, only instead of a single png, it would take 60 pngs per second. At some point, I might actually try to implement exactly that, but I wanted to see if anyone else had something good.

Example So I actually just did an intro using the built in iMovie title cards. This is a good example of roughly the sort of thing I would like to do. Should actually be fairly straightforward with a little CSS3 animation work. What I have isn't bad, but I would like to use custom graphics, with better font/layout control.

回答1:

There is a tutorial with the code using both javascript and PHP to create a video from your canvas animation. The program save frame by frame of your canvas animation like in a movie, and then you can convert this stack of frames to a specific video format with the codec of your choice.

Code from the linked page.

(function () {
    var canvas = document.getElementById('c'),
        c = canvas.getContext('2d'),
        w = canvas.width, h = canvas.height,
        p = [], clr, n = 200;

    clr = [ 'red', 'green', 'blue', 'yellow', 'purple' ];

    for (var i = 0; i < n; i++) {
        // generate particle with random initial velocity, radius, and color
        p.push({
            x: w/2,
            y: h/2,
            vx: Math.random()*12-6,
            vy: Math.random()*12-6,
            r: Math.random()*4+3,
            clr: Math.floor(Math.random()*clr.length)
        });
    }

    function frame() {
        // cover the canvas with 50% opacity (creates fading trails)
        c.fillStyle = 'rgba(0,0,0,0.5)';
        c.fillRect(0, 0, w, h);

        for (var i = 0; i < n; i++) {
            // reduce velocity to 99%
            p[i].vx *= 0.99;
            p[i].vy *= 0.99;

            // adjust position by the current velocity
            p[i].x += p[i].vx;
            p[i].y += p[i].vy;

            // detect collisions with the edges
            if (p[i].x < p[i].r || p[i].x > w-p[i].r) {
                // reverse velocity (direction)
                p[i].vx = -p[i].vx;
                // adjust position again (in case it already passed the edge)
                p[i].x += p[i].vx;
            }
            // see above
            if (p[i].y < p[i].r || p[i].y > h-p[i].r) {
                p[i].vy = -p[i].vy;
                p[i].y += p[i].vy;
            }

            // draw the circle at the new postion
            c.fillStyle = clr[p[i].clr]; // set color
            c.beginPath();
            c.arc(p[i].x, p[i].y, p[i].r, 0, Math.PI*2, false);
            c.fill();
        }
    }

    // execute frame() every 30 ms
    setInterval(frame, 30);
}());

回答2:

Well Techsmith Snagit captures in AVI, or their premium application camtasia ( generates a Flash video and a web page launcher) would work. Why not simply create a Powerpoint slide of the features you want to touch on and use a HTML set of pages of actual demos you want to illustrate in depth. This is the approach I am taking.

回答3:

So far the best thing I've found so far that won't require me to write c code is using Titanium for desktop. It features a takeScreenshot function available from javascript code. The takeScreenshot function gets a screenshot of the entire desktop, but it should be easy to automate cropping that down. With a plethora of javascript animation libraries out there, I should be able to hack in ways of getting a screenshot at every frame, even if it can't happen in real-time.

While I won't be able to use CSS animations, this is probably the most flexible solution anyway, given that anything I can do with CSS animations I can do with javascript, and I'll have more control over frame rate, etc.

Additionally, this should allow me to use all things the browser is capable of, combining html/css/js/svg/canvas.

回答4:

You are right in my opinion the best way to do it is to create images from the canvas's data and then compile all those images into a video via a module (fluent-ffmpeg for example, which is a node js package). It's pretty easy but be careful of the FPS (frame rate) if you create those images as fast as you can you may change the fps of your video, for example if you use recursively requestAnimationFrame() you will be at 60fps. So, instead of reading a html5 video you should set the time each 1/30s (for example if you want a 30fps video) and create a image from the currentTime until the end of the video. And if you have not only one canvas, if you apply animations on your video via multiple canvas you could create a new empty canvas and draw all canvas's data on it to create only one image instead of one image for each canvas.

Cheers from france

回答5:

I had worked on a tool that does something similar to your requirements. It basically uses cutycapt (or any other tool to convert HTML with CSS into image) and takes series of screenshot depending on the frame rate required.

For that to work, the animations should be purely CSS animations and the tool interpolates the intermediate frame's CSS properties by parsing the CSS.

https://github.com/bpsagar/css2video

I'm not sure if the tool is complete, let me know if you are interested.

回答6:

I have done in the past through online site. I had uploaded html5 animation to the site http://html5animationtogif.com and got the animated GIF file. After that, I uploaded my gif file to https://cloudconvert.com/gif-to-mp4 and got the MP4 file. This was my way to convert html5 animation to MP4. Not sure this was a best way. But it worked for me. Hope this answer helps.

回答7:

How about recording the screen with something like http://danicsoft.com/software/copernicus/ ?