Capture, encode then stream video from an iPhone to a server

Question

I've got experience with building iOS apps but don't have experience with video. I want to build an iPhone app that streams real time video to a server. Once on the server I will deliver that video to consumers in real time.

I've read quite a bit of material. Can someone let me know if the following is correct and fill in the blanks for me.

1. To record video on the iPhone I should use the AVFoundation classes. When using the AVCaptureSession the delegate method captureOutput:didOutputSampleBuffer::fromConnection I can get access to each frame of video. Now that I have the video frame I need to encode the frame
   
   • I know that the Foundation classes only offer H264 encoding via AVAssetWriter and not via a class that easily supports streaming to a web server. Therefore, I am left with writing the video to a file.
   • I've read other posts that say they can use two AssetWritters to write 10 second blocks then NSStream those 10 second blocks to the server. Can someone explain how to code the use of two AVAssetWriters working together to achieve this. If anyone has code could they please share.

Answer 1

You are correct that the only way to use the hardware encoders on the iPhone is by using the AVAssetWriter class to write the encoded video to a file. Unfortunately the AVAssetWriter does not write the moov atom to the file (which is required to decode the encoded video) until the file is closed.

Thus one way to stream the encoded video to a server would be to write 10 second blocks of video to a file, close it, and send that file to the server. I have read that this method can be used with no gaps in playback caused by the closing and opening of files, though I have not attempted this myself.

I found another way to stream video here.

This example opens 2 AVAssetWriters. Then on the first frame it writes to two files but immediately closes one of the files so the moov atom gets written. Then with the moov atom data the second file can be used as a pipe to get a stream of encoded video data. This example only works for sending video data but it is very clean and easy to understand code that helped me figure out how to deal with many issues with video on the iPhone.