I am currently in the research and prototyping stages of a project to develop a native iOS app (Swift 3) that includes a multi-channel audio player (multiple stereo MP3 files). I have found very limited information online, particularly written in Swift 3, so thought as I continue my research I would pose a question here.
Regarding frameworks it seems clear from what I've looked at so far that AVFoundation is going to do the job. It's not too low level and has a good set of functionality. It has support for playing multiple audio files with AVAudioPlayer. I am planning to start prototyping something with this soon.
But I am new to Swift and to iOS development with its huge number of libraries, so I'm wondering if I'm missing anything, if I'm on the right track here. Any answers with general information and thoughts on this will be up-voted. For an accepted answer some sample outline code using an appropriate framework, AVFoundation or a justified alternative.
If no answer is forthcoming I will post my own code when I get there.
Specifically I need from two to ten input channels, from MP3 files within the project resources, each with their own gain that can be individually adjusted, and then all of these mixed, maintaining their stereo channels, to a single output (the device) with a master gain. Some of the tracks need to loop, others not. The tracks need to be accurately synchronised. This is just for info and outline code would be fine covering the important points.
Research Notes and Resources
Apple: AVFoundation
A collection of resources relating to AVFoundation.
Apple: AVFoundation Programming Guide
This document seems encouraging at first, but actually only deals with video. It says:
There are two facets to the AVFoundation framework—APIs related to video and APIs related just to audio. The older audio-related classes provide easy ways to deal with audio. They are described in the Multimedia Programming Guide, not in this document.
The "Multimedia Programming Guide" which is also mentioned elsewhere at Apple in relation to this, is never linked and Google results point to not found pages on the Apple site. It seems to have disappeared.
Rudi Strahl: Mixing Multiple Audio Tracks with AVFoundation
Compares using AVComposition to using multiple AVPlayers. Example code is Objective-C. Not sure how the AVPlayers are mixed in the second solution. Perhaps with AVAudioMix. Currently looking at this. The article talks a little about it but doesn't deliver any specifics.
Audio Session Programming Guide
This document looks at AVAudioSession which provides supporting functionality:
AVAudioSession gives you control your app’s audio behavior. You can:
Select the appropriate input and output routes for your app
Determine how your app integrates audio from other apps
Handle interruptions from other apps
Automatically configure audio for the type of app your are creating
Techotopia: Playing Audio on iOS 10 using AVAudioPlayer
Some useful information on using AVAudioPlayer.
Stack Overflow: Playing a Sound with AVAudioPlayer
Basic Swift code for playing a sound. Some answers include a little extra functionality.
Hacking with Swift: How to Play Sounds Using AVAudioPlayer
Again, covers the basics.
Sweet Tutos: How To Play Sounds Files And Manage Duration Progress – AVAudioPlayer Tutorial
Updated to Swift 3. Some useful info.
Xamarin: Playing Sound with AVAudioPlayer
Written in Swift 2, I think.
Apple Video: WWDC 2013 Moving to AV Kit and AV Foundation
While not directly related, I found the first 30 minutes of this video introducing developers to AV Kit and AV Foundation in OS X 10 provides a useful overview of the technology.
I was working on the same problem, best what I could do it is, to transcode media content to be playing using avplayer, here is a draft, maybe it can help.
Related
I'm trying to find a way to get the average power level for a channel, that comes out from the audio played in the embedded video. I'm using YouTube's iOS helper library for embedding the video https://developers.google.com/youtube/v3/guides/ios_youtube_helper
A lot of the answers I've found in StackOverflow refer to AVAudioPlayer, but that's not my case. I also looked in the docs of AudioKit framework to find something that can give the output level of the current audio, but I couldn't find anything related, maybe I missed something over there. I also looked in EZAudio framework even tough it's deprecated, and I also couldn't find something that relates to my case.
My direction of thinking was to find a way to get the actual level that's coming out from the device, but I found one answer in SO that's saying this is not allowed in iOS, although he didn't mention any source for this statement.
https://stackoverflow.com/a/12664340/4711172
So, any help would be much appreciated.
The iOS security sandbox blocks apps from seeing the device's digital audio output stream, or any other app's internal audio output (unless explicitly shared, e.g. inter-app audio, etc.) (when using Apple App store permitted public APIs.)
(Just a guess, but this was possibly and originally implemented in iOS to prevent apps from capturing samples of DRM'd music and/or recording phone call conversations.)
Might be a bit off/weird, but just in case -
Have you considered closing a loop? Meaning - record the incoming audio using 'AVAudioRecorder' and get the audio levels from there?.
See Apple's documentation for AVAudioRecorder (in the overview they're specifying: "Obtain input audio-level data that you can use to provide level metering")
AVAudioRecorder documentation
I would like to modulate the signal from the mic input with a sine wave at 200HZ (FM only). Anyone know of any good tutorials/articles that will help get me started?
Any info is very welcome
Thanks
I suggest you start here Audio File Stream Services Reference
Here you can also find some basic tutorials: Getting Started with Audio & Video.
Especially the SpeakHere example app could be interesting
Hope that helps you
The standard way to do audio processing in iOS or OSX is Core Audio. Here's Apple's overview of the framework.
However, Core Audio has a reputation of being very difficult to learn, especially if you don't have experience with C. If you're still wanting to learn Core Audio, then this book is the way to go: Learning Core Audio.
There are simpler ways to work with audio on iOS and OSX, one of them being AudioKit, which was developed specifically so developers can quickly prototype audio without having to deal with lower-level memory management, buffers, and pointer arithmetic.
There are examples showing both FM synthesis and audio input via the microphone, so you should have everything you need :)
Full disclosure: I am one of the developers of AudioKit.
I'm trying to put together an open source library that allows iOS devices to play files with unsupported containers, as long as the track formats/codecs are supported. e.g.: a Matroska video (MKV) file with an H264 video track and an AAC audio track. I'm making an app that surely could use that functionality and I bet there are many more out there that would benefit from it. Any help you can give (by commenting here or—even better— collaborating with me) is much appreciated. This is where I'm at so far:
I did a bit of research trying to find out how players like AVPlayerHD or Infuse can play non-standard containers and still have hardware acceleration. It seems like they transcode small chunks of the whole video file and play those in sequence instead.
It's a good solution. But if you want to throw that video to an Apple TV, things don't work as planned since the video is actually a bunch of smaller chunks being played as a playlist. This site has way more info, but at its core streaming to Apple TV is essentially a progressive download of the MP4/MPV file being played.
I'm thinking a sort of streaming proxy is the way to go. For the playing side of things, I've been investigating AVSampleBufferDisplayLayer (more info here) as a way of playing the video track. I haven't gotten to audio yet. Things get interesting when you think about the AirPlay side of things: by having a "container proxy", we can make any file look like it has the right container without the file size implications of transcoding.
It seems like GStreamer might be a good starting point for the proxy. I need to read up on it; I've never used it before. Does this approach sound like a good one for a library that could be used for App Store apps?
Thanks!
Finally got some extra time to go over GStreamer. Especially this article about how it is already updated to use the hardware decoding provided by iOS 8. So no need to develop this; GStreamer seems to be the answer.
Thanks!
The 'chucked' solution is no longer necessary in iOS 8. You should simply set up a video decode session and pass in NALUs.
https://developer.apple.com/videos/wwdc/2014/#513
I am developing an architecture for digital audio workstation that works on iOS (mainly, but trying to support OS X too). I'm going slowly through miles of documentation by Apple and references of their frameworks.
I have experience with DSP, but iOS is more new to me and there are so many objects, tutorials (even for older versions of iOS) and different frameworks with different API's. I would just like to make sure I choose the right one on start, or combination of those.
The goals of the architecture are:
Sound track sample access (access samples in files)
iPod library songs
local file songs
songs on remote server
radio stations (infinite length songs)
Effect chaining (multiple equalizers, or pitch & tempo change at the same time)
Multiple channels and mixing (even surround)
Portability
Mac OS X at least
iOS 6+ support (iOS 5 or lower not needed)
Sample access in 32-bit floats, not signed integers.
Easy Objective-C API (DSP and processing done in C++ of course)
Recording, playing
Record to file (codec by choice), or send over network (VoIP)
Playing on different outputs (on Mac) or speakers/headphones on iOS
Changing of volume/mute
Background audio support
Real-time sample processing
Equalizer on any song that is currently played
Real-time sample manipulation
Multi-threading
I hope I did not miss anything, but those are the most important goals.
My research
I have looked through most of the frameworks (not so much in detail though) and here is what I have figured out. Apple lists following frameworks for using Audio on iOS:
Media Player framework
AV Foundation framework
Audio Toolbox framework
Audio Unit framework
OpenAL framework
Media Player and AV Foundation are too high-level API's and do not allow direct sample access. OpenAL on the other side cannot record audio. So that leaves Audio Toolbox and Audio Unit frameworks. Many of the differences are explained here: What's the difference between all these audio frameworks?
As much as I can understand, Audio Toolbox would be the way to go, since MIDI is currently not required. But there is very little information and tutorials on Audio Toolbox for more professional control, such as recording, playing, etc. There is much more on Audio Units though.
My first question: What exactly are Audio Queue Services and what framework they belong to?
And then the final question:
Which framework should be used to be able to achieve most of the desired goals?
You can suggest even mix and match of frameworks, classes, but I ask you kindly, to explain your answer and which classes would you use to achieve a goal in more detail. I encourage highest level API as possible, but as low level as it is needed to achieve the goals. Sample code links are also welcome.
Thank you very much for your help.
Audio Units is the lowest level iOS audio API, and the API that Audio Queues are built upon. And Audio Units will provide an app with the lowest latency, and thus closest to real-time processing possible. It is a C API though, so an app may have to do some of its own audio memory management.
The AVFoundation framework may provide an app with easier access to music library assets.
An app can only process sound from other apps that explicitly publish their audio data, which does not include the Music player app, but does include some of the apps using Apple's Inter-App Audio API, and the 3rd party Audiobus API.
I've read quite a bit both here (Audio Framework in iPhone) and abroad but am still confused as to which Audio Framework to use.
I'm able to get some easier things done, like recording and playing back but I'm looking to the future of the app where I'll be doing more complex things, like managing past recordings (although maybe that's a NSURL bookmark thing) and editing audio.
Right now I'm using AVFoundation but have started reading the docs for Core Audio (and there's also AudioToolbox). I wish there was a developer doc called "Understanding the Different Audio Frameworks and How and When to use them" because, well, the docs are dense and I'm having trouble figuring out which path to go down.
Links to good docs would also be much appreciated!
I recommend you take a look at the recent Learning Core Audio book. The purpose of it was to disambiguate the confusion around audio frameworks on Mac OS and iOS. If you want "good docs", it's well worth getting.
Depending on your requirements, you might also want to consider some of the non-Apple audio frameworks, particularly the MoMu release of STK, which in may respects will be simpler and easier-to-use than Apple's frameworks.