是否可以在iOS中将视频用作GL的纹理? [英] Is it possible using video as texture for GL in iOS?

问题描述

是否可以在iOS中使用视频(预渲染，用H.264压缩)作为GL的纹理?

Is it possible using video (pre-rendered, compressed with H.264) as texture for GL in iOS?

如果可能的话，该怎么做?还有播放质量/帧率或限制吗?

If possible, how to do it? And any playback quality/frame-rate or limitations?

推荐答案

从iOS 4.0开始，您可以使用AVCaptureDeviceInput获取相机作为设备输入，并将其与您设置的任何对象连接到AVCaptureVideoDataOutput作为代表.通过为摄像机设置32bpp BGRA格式，委托对象将以恰好适合立即传送到glTexImage2D(或glTexSubImage2D的完美格式)从摄像机接收每个帧(如果设备不支持不供电的话).两种纹理；我认为MBX设备属于此类).

As of iOS 4.0, you can use AVCaptureDeviceInput to get the camera as a device input and connect it to a AVCaptureVideoDataOutput with any object you like set as the delegate. By setting a 32bpp BGRA format for the camera, the delegate object will receive each frame from the camera in a format just perfect for handing immediately to glTexImage2D (or glTexSubImage2D if the device doesn't support non-power-of-two textures; I think the MBX devices fall into this category).

有一堆帧大小和帧速率选项；猜测您将不得不根据您要使用GPU的数量进行调整.我发现一个完全琐碎的场景，只有带纹理的四边形显示最新的帧，仅当新帧到达iPhone 4时才重绘，该场景能够显示该设备的最大720p 24fps提要，而不会出现任何明显的延迟.除此以外，我还没有进行更全面的基准测试，因此希望其他人可以提供建议.

There are a bunch of frame size and frame rate options; at a guess you'll have to tweak those depending on how much else you want to use the GPU for. I found that a completely trivial scene with just a textured quad showing the latest frame, redrawn only exactly when a new frame arrives on an iPhone 4, was able to display that device's maximum 720p 24fps feed without any noticeable lag. I haven't performed any more thorough benchmarking than that, so hopefully someone else can advise.

原则上，根据API，帧可以在扫描线之间返回一些内存中的填充，这意味着在将内容发布到GL之前需要对内容进行一些改组，因此您需要为此实现代码路径.实际上，纯粹凭经验来讲，似乎当前版本的iOS绝不会以这种形式返回图像，因此这实际上并不是性能问题.

In principle, per the API, frames can come back with some in-memory padding between scanlines, which would mean some shuffling of contents before posting off to GL so you do need to implement a code path for that. In practice, speaking purely empirically, it appears that the current version of iOS never returns images in that form so it isn't really a performance issue.

现在已经非常接近三年了.在此期间，苹果公司发布了iOS 5、6和7.在5中，他们引入了CVOpenGLESTexture和CVOpenGLESTextureCache，它们现在是将视频从捕获设备传输到OpenGL的明智方法. Apple在此处提供示例代码，RippleViewController.m中特别有趣的部分，特别是setupAVCapture和captureOutput:didOutputSampleBuffer:fromConnection: —参见196-329行.可悲的是，条款和条件阻止了此处代码的重复而不附加整个项目，但分步设置为:

it's now very close to three years later. In the interim Apple has released iOS 5, 6 and 7. With 5 they introduced CVOpenGLESTexture and CVOpenGLESTextureCache, which are now the smart way to pipe video from a capture device into OpenGL. Apple supplies sample code here, from which the particularly interesting parts are in RippleViewController.m, specifically its setupAVCapture and captureOutput:didOutputSampleBuffer:fromConnection: — see lines 196–329. Sadly the terms and conditions prevent a duplication of the code here without attaching the whole project but the step-by-step setup is:

1. 创建一个CVOpenGLESTextureCacheCreate和一个AVCaptureSession;
2. 为视频获取合适的AVCaptureDevice；
3. 使用该捕获设备创建一个AVCaptureDeviceInput；
4. 附加一个AVCaptureVideoDataOutput并告诉它调用您作为样本缓冲区委托.

1. create a CVOpenGLESTextureCacheCreate and an AVCaptureSession;
2. grab a suitable AVCaptureDevice for video;
3. create an AVCaptureDeviceInput with that capture device;
4. attach an AVCaptureVideoDataOutput and tell it to call you as a sample buffer delegate.

在收到每个样本缓冲区后:

Upon receiving each sample buffer:

1. 从中获取CVImageBufferRef；
2. 使用CVOpenGLESTextureCacheCreateTextureFromImage从CV图像缓冲区获取Y和UV CVOpenGLESTextureRef；
3. 从CV OpenGLES纹理引用中获取纹理目标和名称以进行绑定；
4. 在着色器中组合亮度和色度.

1. get the CVImageBufferRef from it;
2. use CVOpenGLESTextureCacheCreateTextureFromImage to get Y and UV CVOpenGLESTextureRefs from the CV image buffer;
3. get texture targets and names from the CV OpenGLES texture refs in order to bind them;
4. combine luminance and chrominance in your shader.

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