什么技术最适合将iPhone视频摄像机数据直播到计算机？

Question

I would like to stream video from an iPhone camera to an app running on a Mac. Think sorta like video chat but only one way, from the device to a receiver app (and it's not video chat).

My basic understanding so far:

1. You can use AVFoundation to get 'live' video camera data without saving to a file but it is uncompressed data and thus I'd have to handle compression on my own.
2. There's no built in AVCaptureOutput support for sending to a network location, I'd have to work this bit out on my own.

Am I right about the above or am I already off-track?

Apple Tech Q&A 1702 provides some info on saving off individual frames as images - is this the best way to go about this? Just saving off 30fps and then something like ffmpeg to compress 'em?

There's a lot of discussion of live streaming to the iPhone but far less info on people that are sending live video out. I'm hoping for some broad strokes to get me pointed in the right direction.

Answer 1

You can use AVCaptureVideoDataOutput and a sampleBufferDelegate to capture raw compressed frames, then you just need to stream them over the network. AVFoundation provides an API to encode frames to local video files, but doesn't provide any for streaming to the network. Your best bet is to find a library that streams raw frames over the network. I'd start with ffmpeg; I believe libavformat supports RTSP, look at the ffserver code.

Note that you should configure AVCaptureVideoDataOutput to give you compressed frames, so you avoid having to compress raw video frames without the benefit of hardware encoding.

Answer 2

This depends a lot on your target resolution and what type of frame rate performance you are targeting.

From an abstract point of view, I would probably have a capture thread to fill a buffer directly from AVCaptureOutput, and a communications thread to send and rezero the buffer (padded if need be) to a previously specified host every x milliseconds.

After you accomplish initial data transfer, I would work on achieving 15fps at the lowest resolution, and work my way up until the buffer overflows before the communication thread can transmit which would require balancing image resolution, buffer size (probably dependent on GSM, and soon to be CDMA frame sizes), and finally the maximum rate at which you can transmit that buffer.