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• Mobile Camera live audio/video streaming and encoding

  7 juin 2015, par Strikecounter2

  I know this question has been asked a couple of times, but I still haven’t found the right answer for my question.

  I would like to code an app that is able to live-stream audio and video while the content is being recorded and then uploaded to a server. I’d prefer to have my own back-end using Parse, because I want a high scalability. I know that the video has to be encoded to a h.264 codec and the audio to an AAC codec, but I don’t know how to achieve this. I have heard of the FFmpeg framework, but I am not sure if I would violate their license if I distribute my app or even sell it to somebody else.
  I would then like to receive the stream from the server to open it on the iPhone/android phone.

  They key requirements would be :

  • Low Latency
  • About 24 fps
  • Audio/Video in sync
  • No buffering while watching

  I would like to use Swift as a programming language, but if there is no way to use a swift-wrapper for any frameworks I would focus on Objective-C too.

  I am willing to learn everything that is needed, but I don’t know where to start.

• How do I upscale an iOS App Preview video to 1080 x 1920 ?

  30 août 2016, par Benjamin Thiel

  I just captured a video of my new app running on an iPhone 6 using QuickTime Player and a Lightning cable. Afterwards I created an App Preview project in iMovie, exported it and could successfully upload it to iTunes Connect.

  Apple requires developers to upload App Previews in different resolutions dependent on screen size, namely :

  • iPhone 5(S) : 1080 x 1920 or 640 x 1136
  • iPhone 6 : 750 x 1334 (what I have)
  • iPhone 6+ : 1080 x 1920

  Obviously, 1080 x 1920 is killing two birds with one stone. I know that upscaling isn’t the perfect solution, but it’s meeting my needs. Since I don’t own a 6+, another recording session won’t do the trick.

  Unfortunately, iTunes Connect is extremely picky about what to accept. Here’s what I tried, to no avail :

  • Handbrake, iMovie, QuickTime do not support upscaling
  • MPEG Streamclip
  • ffmpeg -i input.mp4 -acodec copy -vf scale=1080:1920 output.mp4

  Strangely enough, iTunes Connect keeps complaining about the wrong resolution when I try to upload the output.mp4 of ffmpeg.

• What is the bitrate of my audio file based on ffmpeg output ?

  21 avril 2015, par blueether

  Is it the 40kb/s under Format, or is it the 16kb/s under Stream ? What is the relationship between the Format and the Stream ?
  The below output is for a file generated using Core Audio on an iphone, with an Audio Unit. The output format was specified by an AudioStreamBasicDescription descriptor

  Updated :
  Output from ffprobe -v error -show_format -show_streams 123_1429602551009.051025.m4a :

  [STREAM]
  
  index=0
  
  codec_name=aac
  
  codec_long_name=AAC (Advanced Audio Coding)
  
  profile=LC
  
  codec_type=audio
  
  codec_time_base=1/8000
  
  codec_tag_string=mp4a
  
  codec_tag=0x6134706d
  
  sample_fmt=fltp
  
  sample_rate=8000
  
  channels=1
  
  channel_layout=mono
  
  bits_per_sample=0
  
  id=N/A
  
  r_frame_rate=0/0
  
  avg_frame_rate=0/0
  
  time_base=1/8000
  
  start_pts=0
  
  start_time=0.000000
  
  duration_ts=43008
  
  duration=5.376000
  
  bit_rate=16501
  
  max_bit_rate=N/A
  
  bits_per_raw_sample=N/A
  
  nb_frames=42
  
  nb_read_frames=N/A
  
  nb_read_packets=N/A
  
  DISPOSITION:default=1
  
  DISPOSITION:dub=0
  
  DISPOSITION:original=0
  
  DISPOSITION:comment=0
  
  DISPOSITION:lyrics=0
  
  DISPOSITION:karaoke=0
  
  DISPOSITION:forced=0
  
  DISPOSITION:hearing_impaired=0
  
  DISPOSITION:visual_impaired=0
  
  DISPOSITION:clean_effects=0
  
  DISPOSITION:attached_pic=0
  
  TAG:creation_time=1970-04-16 22:36:01
  
  TAG:language=eng
  
  [/STREAM]
  
  [FORMAT]
  
  filename=123_1429602551009.051025.m4a
  
  nb_streams=1
  
  nb_programs=0
  
  format_name=mov,mp4,m4a,3gp,3g2,mj2
  
  format_long_name=QuickTime / MOV
  
  start_time=0.000000
  
  duration=5.376000
  
  size=27473
  
  bit_rate=40882
  
  probe_score=100
  
  TAG:major_brand=M4A
  
  TAG:minor_version=0
  
  TAG:compatible_brands=M4A mp42isom
  
  TAG:creation_time=1970-04-16 22:36:01
  
  TAG:iTunSMPB= 00000000 00000840 00000361 0000000000009C5F 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
  
  [/FORMAT]