将iphone相机直播到媒体服务器的最佳方式是什么？

Question

According to this What Techniques Are Best To Live Stream iPhone Video Camera Data To a Computer? is possible to get compressed data from iphone camera, but as I've been reading in the AVFoundation reference you only get uncompressed data.

So the questions are:

1) How to get compressed frames and audio from iPhone's camera?

2) Encoding uncompressed frames with ffmpeg's API is fast enough for real-time streaming?

Any help will be really appreciated.

Thanks.

Answer 1

You most likely already know....

1) How to get compressed frames and audio from iPhone's camera?

You can not do this. The AVFoundation API has prevented this from every angle. I even tried named pipes, and some other sneaky unix foo. No such luck. You have no choice but to write it to file. In your linked post a user suggest setting up the callback to deliver encoded frames. As far as I am aware this is not possible for H.264 streams. The capture delegate will deliver images encoded in a specific pixel format. It is the Movie Writers and AVAssetWriter that do the encoding.

2) Encoding uncompressed frames with ffmpeg's API is fast enough for real-time streaming?

Yes it is. However, you will have to use libx264 which gets you into GPL territory. That is not exactly compatible with the app store.

I would suggest using AVFoundation and AVAssetWriter for efficiency reasons.

Answer 2

I agree with Steve. I'd add that on trying with Apple's API, you're going to have to do some seriously nasty hacking. AVAssetWriter by default spends a second before spilling its buffer to file. I haven't found a way to change that with settings. The way around that seems to be to force small file writes and file close with the use of multiple AVAssetWriters. But then that introduces lots of overhead. It's not pretty.

Definitely file a new feature request with Apple (if you're an iOS developer). The more of us that do, the more likely they'll add some sort of writer that can write to a buffer and/or to a stream.

One addition I'd make to what Steve said on the x264 GPL issue is that I think you can get a commercial license for that which is better than GPL, but of course costs you money. But that means you could still use it and get pretty OK results, and not have to open up your own app source. Not as good as an augmented Apple API using their hardware codecs, but not bad.