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• How to deal with cv::VideoCapture decode errors ?

  24 février 2016, par George Profenza

  I’m streaming H264 content from an IP camera using the VideoCapture from OpenCV (compiled with ffmpeg support).

  So far things work ok, but every once in a while I get decoding errors (from ffmpeg I presume) :

  [h264 @ 0x103006400] mb_type 137 in I slice too large at 26 10
  
  [h264 @ 0x103006400] error while decoding MB 26 10
  
  [h264 @ 0x103006400] negative number of zero coeffs at 25 5
  
  [h264 @ 0x103006400] error while decoding MB 25 5
  
  [h264 @ 0x103006400] cbp too large (421) at 35 13
  
  [h264 @ 0x103006400] error while decoding MB 35 13
  
  [h264 @ 0x103006400] mb_type 121 in P slice too large at 20 3
  
  [h264 @ 0x103006400] error decoding MB 20 3

  These messages show up in the console. Is there any clean way to listen to these ? I’d like to skip processing the glitchy frames.

  Any hints/tips ?

• How to build and link FFMPEG to iOS ?

  30 juin 2015, par Alexander Tkachenko

  all !

  I know, there are a lot of questions here about FFMPEG on iOS, but no one answer is appropriate for my case :(
  Something strange happens each case when I am trying to link FFMPEG in my project, so please, help me !

  My task is to write video-chat application for iOS, that uses RTMP-protocol for publishing and reading video-stream to/from custom Flash Media Server.

  I decided to use rtmplib, free open-source library for streaming FLV video over RTMP, as it is the only appropriate library.

  Many problem appeared when I began research of it, but later I understood how it should work.

  Now I can read live stream of FLV video(from url) and send it back to channel, with the help of my application.

  My trouble now is in sending video FROM Camera.
  Basic operations sequence, as I understood, should be the following :

  1. Using AVFoundation, with the help of sequence (Device-AVCaptureSession-AVVideoDataOutput-> AVAssetWriter) I write this to a file(If you need, I can describe this flow more detailed, but in the context of question it is not important). This flow is necessary to make hardware-accelerated conversion of live video from the camera into H.264 codec. But it is in MOV container format. (This is completed step)

  2. I read this temporary file with each sample written, and obtain the stream of bytes of video-data, (H.264 encoded, in QuickTime container). (this is allready completed step)

  3. I need to convert videodata from QuickTime container format to FLV. And it all in real-time.(packet - by - packet)

  4. If i will have the packets of video-data, contained in FLV container format, I will be able to send packets over RTMP using rtmplib.

  Now, the most complicated part for me, is step 3.

  I think, I need to use ffmpeg lib to this conversion (libavformat). I even found the source code, showing how to decode h.264 data packets from MOV file (looking in libavformat, i found that it is possible to extract this packets even from byte stream, which is more appropriate for me). And having this completed, I will need to encode packets into FLV(using ffmpeg or manually, in a way of adding FLV-headers to h.264 packets, it is not problem and is easy, if I am correct).

  FFMPEG has great documentation and is very powerfull library, and I think, there won’t be a problem to use it. BUT the problem here is that I can not got it working in iOS project.

  I have spend 3 days reading documentation, stackoverflow and googling the answer on the question "How to build FFMPEG for iOS" and I think, my PM is gonna fire me if I will spend one more week on trying to compile this library :))

  I tried to use many different build-scripts and configure files, but when I build FFMPEG, i Got libavformat, libavcodec, etc. for x86 architecture (even when I specify armv6 arch in build-script). (I use "lipo -info libavcodec.a" to show architectures)

  So I cannot build this sources, and decided to find prebuilt FFMPEG, that is build for architecture armv7, armv6, i386.

  I have downloaded iOS Comm Lib from MidnightCoders from github, and it contains example of usage FFMPEG, it contains prebuilt .a files of avcodec,avformat and another FFMPEG libraries.

  I check their architecture :

  iMac-2:MediaLibiOS root# lipo -info libavformat.a
  
  Architectures in the fat file: libavformat.a are: armv6 armv7 i386 

  And I found that it is appropriate for me !
  When I tried to add this libraries and headers to xCode project, It compiles fine(and I even have no warnings like "Library is compiled for another architecture"), and I can use structures from headers, but when I am trying to call C-function from libavformat (av_register_all()), the compiler show me error message "Symbol(s) not found for architecture armv7 : av_register_all".

  I thought, that maybe there are no symbols in lib, and tried to show them :

  root# nm -arch armv6 libavformat.a | grep av_register_all
  
  00000000 T _av_register_all

  Now I am stuck here, I don’t understand, why xCode can not see this symbols, and can not move forward.

  Please, correct me if I am wrong in the understanding of flow for publishing RTMP-stream from iOS, and help me in building and linking FFMPEG for iOS.

  I have iPhone 5.1. SDK and xCode 4.2.

• Truly live streaming to Android/iPhone

  4 juillet 2012, par Tsaukpaetra

  I have spent quite a while (past week) trying this to little avail. However, what I want seems completely unheard of. So far, I have reviewed recommendations available through google, which include encoding a static file into multiple static files in different formats, creating a playlist that hosts static files in an m3u8 file (files which get added to the playlist as streaming continues).
  I have also seen ideas involving rtmp, rtsp etc which are completely out of the question because of their incompatibility.
  Ideally, I would have one webpage that would link to the stream (http://server/video.mp4) and/or show it in a webpage (via the video tag). With that in mind, the most likely format would be h264+aac in mp4 container.

  Unfortunately, (and probably because the file has no duration metadata) it does not work. I can use a desktop player (such as VLC) to open the stream and play it, but my iPhone and Android both give their respective "Can't be played" messages.

  I don't think the problem is caused by the devices' ability to stream, for I have made a streaming shoutcast server work just fine (mp3 only).

  Currently, the closest I have become is using the following setup on my win32 machine :

  FFMPEG Command: : ffmpeg -f dshow -i video="Logitech Webcam 200":audio="Microphone (Webcam 200)" -b:v 180k -bt 240k -vcodec libx264 -tune zerolatency -profile:v baseline -preset ultrafast -r 10 -strict -2 -acodec aac -ac 2 -ar 48000 -ab 32k -f flv "udp ://127.0.0.1:1234"

  VLC: : Stream from udp ://127.0.0.1:1234 to http:// :8080/video.mp4 (No Transcoding), basically just to convert the UDP stream into an http-accessible stream.

  Any hints or suggestions would be warmly welcomed !