I am curious as to how to use libVLC to play segments of a clip downloaded over the network. We are developing sort of a P2P program where packets can have several paths to get to the destination. Once it gets there I need to know how to play it. My idea is that it will be placed in a buffer and the player will play the packets in a FIFO manner.
The code I have is a modified version of this tutorial. I know that it can directly receive streams and pretty much play whatever file we give it. However, I don't know how to do it so that I can place a segment of a file (obtained from the packets) into the buffer and let it play.
A lot of my search results in seeing libvlc_video_set_callbacks() but I fail to see how that helps. If it matters, we are only considering MP4 files for now and will expand later.
Related
I'm working on a personal project where the iPhone connects to a server-type application running on a Mac. The iPhone send and receives textual/ASCII data via standard sockets. I now need to stream the microphone from the Mac to the iPhone. I've done some work with AudioServices before but wanted to check my thoughts here before getting too deep.
I'm thinking I can:
1. Create an Audio Queue in the standard Cocoa application on the Mac.
2. In my Audio Queue Callback function, rather than writing it to a file, write it to another socket I open for audio streaming.
3. On the iPhone, receive the raw sampled/encoded audio data from the TCP stream and dump it into an Audio Queue Player which outputs to headphone/speaker.
I know this is no small task and I've greatly simplified what I need to do but could it be as easy as that?
Thanks for any help you can provide,
Stateful
This looks broadly sensible, but you'll almost certainly need to do a few more things:
Buffering. On the "recording" end, you probably don't want to block the audio queue if the buffer is full. On the "playback" end, I don't think you can just pass buffers into the queue (IIRC you'll need to buffer it until you get a callback).
Concurrency. I'm pretty sure AQ callbacks happen on their own thread, so you'll need some sort of locking/barriers around your buffer accesses.
Buffer pools, if memory allocation ends up being a big overhead.
Compression. AQ might be able to give you "IMA4" frames (IMA ADPCM 4:1, or so); I'm not sure if it does hardware MP3 decompression on the iPhone.
Packetization, if e.g. you need to interleave voice chat with text chat.
EDIT: Playback sync (or whatever you're supposed to call it). You need to be able to handle different effective audio clock rates, whether it's due to a change in latency or something else. Skype does it by changing playback speed (with pitch-correction).
EDIT: Packet loss. You might be able to get away with using TCP over a short link, but that depends a lot on the quality of your wireless network. UDP is a minor pain to get right (especially if you have to detect an MTU hole).
Depending on your data rates, it might be worthwhile going for the lower-level (BSD) socket API and potentially even using readv()/writev().
If all you want is an "online radio" service and you don't care about the protocol used, it might be easier to use AVPlayer/MPMoviePlayer to play audio from a URL instead. This involves implementing a server which speaks Apple's HTTP streaming protocol; I believe Apple has some sample code that does this.
I'd like to get real-time video from the iPhone to another device (either desktop browser or another iPhone, e.g. point-to-point).
NOTE: It's not one-to-many, just one-to-one at the moment. Audio can be part of stream or via telephone call on iphone.
There are four ways I can think of...
Capture frames on iPhone, send
frames to mediaserver, have
mediaserver publish realtime video
using host webserver.
Capture frames on iPhone, convert to
images, send to httpserver, have
javascript/AJAX in browser reload
images from server as fast as
possible.
Run httpServer on iPhone, Capture 1 second duration movies on
iPhone, create M3U8 files on iPhone, have the other
user connect directly to httpServer on iPhone for
liveStreaming.
Capture 1 second duration movies on
iPhone, create M3U8 files on iPhone,
send to httpServer, have the other
user connected to the httpServer
for liveStreaming. This is a good answer, has anyone gotten it to work?
Is there a better, more efficient option?
What's the fastest way to get data off the iPhone? Is it ASIHTTPRequest?
Thanks, everyone.
Sending raw frames or individual images will never work well enough for you (because of the amount of data and number of frames). Nor can you reasonably serve anything from the phone (WWAN networks have all sorts of firewalls). You'll need to encode the video, and stream it to a server, most likely over a standard streaming format (RTSP, RTMP). There is an H.264 encoder chip on the iPhone >= 3GS. The problem is that it is not stream oriented. That is, it outputs the metadata required to parse the video last. This leaves you with a few options.
Get the raw data and use FFmpeg to encode on the phone (will use a ton of CPU and battery).
Write your own parser for the H.264/AAC output (very hard)
Record and process in chunks (will add latency equal to the length of the chunks, and drop around 1/4 second of video between each chunk as you start and stop the sessions).
"Record and process in chunks (will add latency equal to the length of the chunks, and drop around 1/4 second of video between each chunk as you start and stop the sessions)."
I have just wrote such a code, but it is quite possible to eliminate such a gap by overlapping two AVAssetWriters. Since it uses the hardware encoder, I strongly recommend this approach.
We have similar needs; to be more specific, we want to implement streaming video & audio between an iOS device and a web UI. The goal is to enable high-quality video discussions between participants using these platforms. We did some research on how to implement this:
We decided to use OpenTok and managed to pretty quickly implement a proof-of-concept style video chat between an iPad and a website using the OpenTok getting started guide. There's also a PhoneGap plugin for OpenTok, which is handy for us as we are not doing native iOS.
Liblinphone also seemed to be a potential solution, but we didn't investigate further.
iDoubs also came up, but again, we felt OpenTok was the most promising one for our needs and thus didn't look at iDoubs in more detail.
I want to be able to (live) stream the frames/video FROM the iPhone camera to the internet. I've seen in a Thread (streaming video FROM an iPhone) that it's possible using AVCaptureSession's beginConfiguration and commitConfiguration. But I don't know how to start designing this task. There are already a lot of tutorials about how to stream video TO the iPhone, and it is not actually what I am searching for.
Could you guys give me any ideas which could help me further?
That's a tricky one. You should be able to do it, but it won't be easy.
One way that wouldn't be live (not answering your need, but worth mentioning) is to capture from the camera and save it to a video file. see the AV Foundation Guide on how to do that. Once saved you can then use the HTTP Live Streaming segmenter to generate the proper segments. Apple has applications for Mac OSX, but there's an open source version as well that you could adapt for iOS. On top of that, you'd also have to run an http server to serve those segments. Lots of http servers out there you could adapt.
But to do it live, first as you have already found, you need to collect frames from the camera. Once you have those you want to convert them to h.264. For that you want ffmpeg. Basically you shove the images to ffmpeg's AVPicture, making a stream. Then you'd need to manage that stream so that the live streaming segmenter recognized it as a live streaming h.264 device. I'm not sure how to do that, and it sounds like some serious work. Once you've done that, then you need to have an http server, serving that stream.
What might actually be easier would be to use an RTP/RTSP based stream instead. That approach is covered by open source versions of RTP and ffmpeg supports that fully. It's not http live streaming, but it will work well enough.
I can get individual frames from the iPhone's cameras just fine. what I need is a way to package them up with sound for streaming to the server. Sending the files once I have them isn't much of an issue. Its the generation of the files for streaming that I am having problems with. I've been trying to get FFMpeg to work without much luck.
Anyone have any ideas on how I can pull this off? I would like a known working API or instructions on getting FFMpeg to compile properly in an iPhone app.
You could divide your recording to separate files with a length of say, 10sec, then send them separately. If you use AVCaptureSession's beginConfiguration and commitConfiguration methods to batch your output change you shouldn't drop any frames between the files. This has many advantages over frame by frame upload:
The files can be directly used for HTTP live streaming without any server side processing.
The gap between data transfers allow the antennas to sleep in between if the connection is fast enough, saving battery life.
Conversely, if the connection is slow so upload is slower than recording, managing delayed upload of a set of files is much easier than a stream of bytes.
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.