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• Getting accurate time from FFMPeg with Objective C (Audio Queue Services)

  2 avril 2012, par Winston

  My iPhone app plays an audio file using FFMPeg.

  I'm getting the elapsed time (to show to user) from the playing audio (in minutes and seconds after converting from microseconds, given by FFMPeg) like so :

  AudioTimeStamp currentTimeStamp;
  
  AudioQueueGetCurrentTime (audioQueue, NULL, &currentTimeStamp, NULL);
  
  
  
  getFFMPEGtime = currentTimeStamp.mSampleTime/self.basicAudioDescription.mSampleRate;
  
  
  
  self.currentAudioTime = [NSString stringWithFormat: @"%02d:%02d",
  
                              (int) getFFMPEGtime / (int)60000000,
  
                              (int) ((getFFMPEGtime % 60000000)/1000000)];

  Everything works fine, but when I scrub back or forward to play another portion of the song, the elapsed time will go back to zero, no matter the current position. The timer will always zero out.

  I know I'm suposed to do some math to keep track of the old time and the new time, maybe constructing another clock or so, perhaps implementing another callback function, etc... I'm not sure what way I should go.

  My questions are :

  1) What's the best approach to keep track of the elapsed time when going back/forward in a song, avoiding the clock to always going back to zero ?

  2) Should I look deeply into FFMPeg functions or should I stick with Objective-C and Cocoa Touch for solving this problem ?

  Please, I need some advices/ideas from experienced programmers. I'm stuck. Thanks beforehand !

• How can I fix choppy ffmpeg RTP streaming over wifi ?

  19 décembre 2015, par awidgery

  I have a Raspberry Pi, with a USB mic and a WiFi dongle dongle connected.

  I’m trying to stream audio only from the Pi, with the intention of receiving the stream over wifi to a custom iOS mobile app using VLCKit. I’m using ffmpeg on the Pi as I need a reasonably low (<2s) latency for this project, and using Icecast/Darkice gave around 15s latency.

  The code executed on the Pi is :

  ffmpeg -f alsa -i plughw:1,0 -acodec libmp3lame -ab 128k -ac 1 -ar 44100  -f rtp rtp://234.5.5.5:1234

  On the Pi end I have a device playing (Christmas !) music constantly into the USB mic for testing purposes. The Pi is only connected by WiFi - not ethernet.

  For testing receiving the stream, I’m using VLC (on a Macbook/iPhone).

  When the Mac is connected through Ethernet, the stream works fine, as you can see here :

  https://goo.gl/photos/HZgNh7z4HgaqHBaP7

  However, when the Mac is connected via WiFi, the stream is choppy, as you can see here :

  https://goo.gl/photos/qjAVH6djqS9Jbvmh6

  You can also see a ping trace from the Mac to the Pi, and the VLC stats. As you can see there doesn’t seem to be a correlation between either of these and the choppiness.

  I’ve tried the VLC iOS app and the choppiness is the same as the Mac on WiFi.

  How can I decrease/remove this chop, even if doing so increases latency a bit ?

• avformat/mov : Add support for exporting Video Extension Usage info

  30 mai 2024, par Derek Buitenhuis

  avformat/mov : Add support for exporting Video Extension Usage info
  This box is provided by files created by the Apple Vision Pro, as well
  
  as the iPhone 15+ when capture for Vision Pro is enabled.
  The boxes are a mix of things documented by Apple in some PDFs, their
  
  API docs, and reverse engineering. Ideally we will have a real spec
  
  one day.
  Links :
  
    * https://developer.apple.com/av-foundation/Stereo-Video-ISOBMFF-Extensions.pdf
  
    * https://developer.apple.com/documentation/videotoolbox/kvtcompressionpropertykey_horizontaldisparityadjustment
  
    * https://developer.apple.com/documentation/videotoolbox/kvtcompressionpropertykey_stereocamerabaseline
  
    * https://developer.apple.com/documentation/videotoolbox/kvtcompressionpropertykey_heroeye
  Signed-off-by : Derek Buitenhuis <derek.buitenhuis@gmail.com>
  

  • [DH] libavformat/mov.c