I wish to export a sound recording on iOS from an app into some kind of format that's suitable to be sent over email. Since this leaves a compressed format this leaves out uncompressed wav, and leaves a choice of mp3, ogg, m4a..
What readily available libraries (or even APIs) are available in iOS to do this task?
AVFoundation will do the job for you. In particular, you should look at AVExportSession, which is explicity written for encoding pcm into mp3 or m4a. Sorry, no ogg here. This stuff was available since iOS4.
Related
I'm working on an app that will play several audio files. I have gotten that to work, having no trouble. But I'm not sure what file format to use. Right now I am using .wav and one .mp3. Is there a file type that is recommended? I don't know how the app is packaged for the App Store; should the audio be compressed or uncompressed?
Thank you!
It depends on what you're trying to accomplish.
Personally, I favor compression unless quality is an issue. Mp3s, while lossy is my preferred default. It's a standard file type, easy to work with, it can be high quality and iPhone/iOS is efficient at decoding.
However, if you need higher quality, AAC or uncompressed can be better. It's also possible for an mp3 to take a fraction of a second before it starts to play due to decoding. That may or may not be an issue if your audio is tied to a UI event.
An app bundle is the most common way of packaging the executable code(though not the only way.)
I will recommend you to read the following to know about how the bundle structure is.
https://developer.apple.com/library/ios/documentation/CoreFoundation/Conceptual/CFBundles/BundleTypes/BundleTypes.html#//apple_ref/doc/uid/10000123i-CH101-SW1
With regards to the audio file format, There is no favourite as such for apple. You can find the preferred list of audio formats as:
https://developer.apple.com/library/ios/documentation/AudioVideo/Conceptual/MultimediaPG/UsingAudio/UsingAudio.html#//apple_ref/doc/uid/TP40009767-CH2-SW9
Hope this solves your problems.
Problem:
To get an iOS app that streams video accepted into the app store, we need to have a HLS version.
What’s the problem?
Android does not support HLS well, and for other reasons, we need to store MP4 and HLS files of the same content.
What’s the difference between MP4 and HLS and why do you need to store both?
MP4 is a container that stores H.264 video and AAC audio for best compatibility in HTML 5 browsers – jsvideo players often have flash fallback if the browser does not support MP4 video in HTML 5 that use the same MP4 file, but played through flash.
HLS is a protocol where text files (.m3u8) contain references to playlists, which themselves reference .ts files (or m2ts), which are mpeg-2 transport streams, not to be confused with mpeg-2 video. The .ts files are containers for the same H.264 video and AAC audio.
Why am I complaining?
It takes time to create the HLS files and playlists from the MP4 files
(Most importantly) We are now storing twice as much data on S3
Why should I care? If your S3 bill is $10K per month for storing both MP4 and HLS, now it is only $5K. Or put another way, if you are paying $100K for storing data in MP4, it would cost $200K to store the same content in both MP4 and HLS.
What do I want?
I want to store only the .ts files and serve both desktop users, iOS users, and Android users with that single file.
Is it possible?
Doesn’t HLS require 5-10 second .ts segments instead of one big file?
As of IETF draft 7, and version 4 of the protocol, HLS supports the tag EXT-X-BYTERANGE which allows you to specify a media segment as a byte range (subrange) of a larger URL.
Are .ts files compatible with HTML5 video?
Apparently not. They are a different container than MP4, yet contain the same video and audio content. Worth looking into how to store the raw video/audio data once and simply using the correct containers when necessary. If JS video players can convert HTML 5 MP4 files into Flash video on the fly if the browser does not support HTML 5 MP4, then why not be able to do the same with M2TS data?
I might be ignorant on some level, but maybe someone can shed some light on this issue, and possibly present a solution.
There currently is no good solution.
A little background.
Video streaming used to require custom protocols such as RTP/RTMP/RTSP etc. These protocols work fine except, we were basically building two separate networks. One HTTP based for standard web traffic, and the other one. The idea came along to split video into little chunks and serve them to the player over HTTP. This way we do not need special servers/software and we could take advantage of the giant HTTP CDNs that were being built. In addition. because the video was split into chunks, we can can encode the same video into different qualities/file sizes. Then the player can choose the best quality video for its current bandwidth. This was the perfect solution for mobile because of the constant changing network conditions. Several competing standard were developed. Move networks was the first to market [citation needed]. The design was copied by Microsoft (Smooth Streaming) and Apple (HTTP Live streaming aka HLS). Microsoft is phasing out smooth streaming in favor of DASH. DASH looks like it will become the default streaming solution of the future. Except, because of its design-by-comity approach, it has basically been stuck in comity for a few years. Now, in those few years, Apple sold Millions of IOS devices. So HLS can not just be discontinued. Why doesn't everyone just use HLS then? I can think of three reasons 1) Its Apples standard, and people are haters. 2) Transport streams are a complicate file format. and 3) Transport streams a patent encumbered. MP4 is not patent encumbered but it also does not have the adaptive abilities. This make user experience poor on 2G networks. The only network supported by the iPhone 1. Also AT&T at the time did not want full bitrate video streamed over there woefully inadequate celular network. HLS was the compromise. All of this predates HTML5. So the video tag was not even considered in its design.
Addressing your points:
1) It takes time to create the HLS files and playlists from the MP4
files
This is a programing website, Automate it.
2) We are now storing twice as much data on S3
[sic] I want to store only the .ts files and serve both desktop users,
iOS users, and Android users with that single file.
You and me both man :).
Possible solutions.
1) What is specifically wrong with Androids implementation? (except for lack of in older devices)
2) JW player can play HLS (Not sure about on android)
3) Server side transmux on demand.
Doesn’t HLS require 5-10 second .ts segments instead of one big file?
You can do byte-ranges, but you need to make sure all devices you are interested in support it.
If JS video players can convert HTML 5 MP4 files into Flash video on
the fly if the browser does not support HTML 5 MP4, then why not be
able to do the same with M2TS data?
They don't convert. Flash natively supports mp4. It is possible to convert TS in AS3/JS. I have done it. JW player can convert TS in browser. video.js may be able to as well.
I'm creating an AAC encoded m4a file from raw PCM samples for streaming purposes. I'm using AAC hardware encoding provided in this example. iPhoneExtAudioFileConvertTest
Now I would really want to add metadata such as album artwork and titles.
As I understand m4a or mp4 containers are MPEG-4 Part 14. So the specified metadata format is XMP. However I do not know the good tool for working with XMP metadata. Any ideas?
I'm aware of Adobe XMP SDK, but it seems quite heavyweight, maybe there is a better solution for iOS. I mean, I doubt that it's possible to do in AVFoundation, as XMP is Adobe technology, but maybe someone wrote a nice library especially for this purpose.
I don't know in what terms you think XMP SDK to be a heavyweight.But I can assure you that it hardly takes 15 mins to download, compile and start using the SDK.
You could start by editing one of the Samples(Modify) that come with XMP SDK and then use the snippet inside your application.
On an ios device, can AVAssetReaderOutput be told to only use software-based decoders (i.e. kAppleSoftwareAudioCodecManufacturer rather than kAppleHardwareAudioCodecManufacturer)?
I see that this is possible using Audio Format Services in AudioToolbox, but I don't see how to carry this over to AVFoundation.
The reason for this is that I'd like to decode compressed audio from the itunes library while iPodMusicPlayer is playing - since hardware-assisted decoding does not support simultaneous decoding of multiple songs, my app will need to use software decoding (right?)
I'd rather not do the software decoding as a 2-step process (i.e. export compressed file to app sandbox, then open that using AudioToolbox).
Well, although I haven't found a way to specify the software decoder in AVFoundation, I ended up working around this by reading each track of the compressed song file with an AVAssetReaderTrackOutput, then passing the compressed buffers to an AudioConverterRef.
how can i change the constant bitrate(CBR) of mp3 files ? (such as 64kbps - 128kbps - 192kbps)
BASS is a good library for sound handling.
It includes wrappers for Delphi.
Reencoding involves decoding the MP3 files, then encode in a different bitrate.
BASS can natively decode MP3 files and streams.
BASS has encoder-wrappers for various encodings (using external encoders) for instance using LAME for MP3 encoding (the easiest is to pick download a precompiled Lame Bundle).
BASS licensing is free for non-commercial use.
They have a great forum for support.
--jeroen
You need to re-encode the mp3. Since I know of no good mp3 codec written in Delphi you'll need a wrapper around a c library such as lame.
If you have access to the original audio-data (Wave, FLAC,...) then you better encode from the lossless to the new bit-rate since chaining lossy encodes reduces the quality.
You might also need to look into the mp3 licensing terms. Some kinds of usage are free, but you need to pay for others.