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.
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.
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.
Related
I receive raw H.264 NALUs from an IP camera (via Live555) and I want to decode them using hardware because FFmpeg is great but it's too slow (the camera sensor is large).
The only solution I see is to write the NALUs to some movie container file such as MPEG-4, and then read and decode that file using an AVAssetReader.
Am I off in the weeds? Is anyone having success decoding H.264 NALUs from a stream? Does anyone have any tips for writing NALUs to an MPEG-4 file? Other ideas?
Like Matt mentioned, there is no direct access to Apple's H264 decoder.
However, I have had success with ffmpeg and h264 decoding. Like you mentioned, I have built ffmpeg with LGPL I was able to decode H264 streams all the way to real-time HD stream with no latency on both ipad and iphone. Nothing fancy is required from ffmpeg, you can find bunch of standard decoding c++ code that will work just fine on iOS. Also, in my case H264 NALUs were delivered via RTP/RTSP in real-time.
Also, if I was you I would run your app through xcode instruments to truly see where you bottleneck is, but I would be highly surprised it is in ffmpeg decoding step.. Hopefully this info helps.
Unfortunately, you cannot do this at present. Feel free to file a radar with Apple about wanting this sort of access to the hardware decoder. It'll certainly be resolved as a duplicate :-). I assume it is for licensing reasons why they can't give this sort of access to the hardware codec.
So, you're going to have to use a software decoder. Please be aware that if you're going to ship to the App Store then you need something with a non-GPL license (unless you want to open source your app as well).
On iOS, is it possible to get the user's audio stream in a decompressed format? For example, the MP3 is returned as a WAV that can be used for audio analysis? I'm relatively new to the iOS platform, and I remember seeing that this wasn't possible in older iOS versions. I read that iOS 4 brought in some advanced APIs but I'm not sure where I can find documentations/samples for these.
If you don't mind using API for iOS 4.1 and above, you could try using the AVAssetReader class and friends. In this similar question you have a full example on how to extract video frames. I would expect the same to work for audio, and the nice thing is that the reader deals with all the details of decompression. You can even do composition with AVComposition to merge several streams.
These classes are part of the AVFramework, which allows not only reading but also creating your own content.
Apple has an OpenAL example at http://developer.apple.com/library/mac/#samplecode/OpenALExample/Introduction/Intro.html where Scene.m should interest you.
The Apple documentation has this picture where the Core Audio framework clearly shows that it gives you MP3 out. It also states that you can access audio units in a more radical way if you so need.
The same Core Audio document gives also some information about using MIDI if it may help you.
Edit:
You're in luck today.
In this example an audio file is loaded and fed into an AudioUnit graph. You could fairly easily write an AudioUnit of your own to put into this graph and which analyzes the PCM stream as you see fit. You can even do it in the callback function, although that's probably not a good idea because callbacks are encouraged to be as simple as possible.
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:
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.
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.
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.
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.
I'm looking for a way (doesn't need to be app-store save!!) to get ahold of video-streaming-relevant debugging information.
What I'm trying to do, is to write an application that opens a video stream and displays information like:
framerate
bitrate audio / video
etc etc.
codec information
basically i want to display as much information for any given stream.
Thanks for any information in advance,
best regards
sam
Even though you tagged your question with MPMoviePlayerController, that class probably isn't going to help you out very much. First of all, there's a limited amount of information you can access from it at a high level, certainly nothing about codecs and audio bitrate. And even if the class does store this type of information somehow, your app would be disqualified from being in the iTunes App Store if you access non-public methods or properties.
Secondly, MPMoviePlayerController only supports a limited number of codecs itself, namely the ones that can be decoded in hardware on the iPhone/iPad (H.264 baseline and MPEG-4 videos).
Anyways, a good option could be FFMpeg for the iPhone. Getting the information you need seems to be much more straightforward this way; check out this blog post for a nice tutorial for using the libraries.
I'm not sure about the potential legal issues concerning distributing such a program in the App Store, but if you statically link it with your binary that would at least satisfy Apple... you'll have to check the FFMpeg Legal Site for their end.
Using FFMPEG, Live555, JSON
Not sure how it works but if you look at the source files at http://github.com/dropcam/dropcam_for_iphone you can see that they are using a combination of open source projects like FFMPEG, Live555, JSON etc. Using Wireshark to sniff the packets sent from one of the public cameras that's available to view with the free "Dropcam For Iphone App" at the App Store, I was able to confirm that the iphone was receiving H264 video via RTP/RTSP/RTCP and even RTMPT which looks like maybe some of the stream is tunneled?
Maybe someone could take a look at the open source files and explain how they got RTSP to work on the iphone.
Thanks for the info TinC0ils. After digging a little deeper I'v read that they have modified the Axis camera with custom firmware to limit the streaming to just a single 320x240 H264 feed, to better provide a consistent quality video over different networks and, as you point out, be less of a draw on the phone's hardware etc. My interest was driven by a desire to use my iphone to view live video and audio from a couple of IP cameras that I own without the jerkiness of MJPEG or the inherent latency that is involved with "http live streaming". I think Dropcam have done an excellent job with their hardware/software combo, I just don't need any new hardware at the moment.
Oh yeah, I almost forgot the reason of this post RTSP PROTOCOL DOES WORK ON THE IPHONE!
They are using open source projects to receive the frames and decoding in software instead of using hardware decoders. This will work, however, this runs counter to Apple's requirement that you use their HTTP Streaming. It will also require greater CPU resources such that it doesn't decode video at the desired fps/resolution on older devices and/or decrease battery life compared to HTTP streaming.