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• How do I calculate optimal dimensions and bitrate for displaying a video on an iPhone ?

  6 février 2020, par wachutu

  I’m currently developing a mobile app that will have a library of 2-5 minute videos (approx 100 in total) and going through the process of determining which versions of the videos to have ready to serve to different mobile devices. In my research, I have noticed that there is a lot of room to play with video settings such as dimensions and bitrate.

  As a first test, I am attempting to find the minimum video size I can deliver to an iPhone XS with dimensions 1125x2436 without losing any noticeable quality. I started by scaling the video to 1125x2436 and creating versions with 5 different bitrates ranging from 500kbps-4400kbps. I noticed that at 1500kbps, the video looks great and the size is cut 1/3 so that was a good start.

  Then after doing some reading, I saw that in adaptive bitrate scenarios Apple recommends delivering video of lower bitrate AND lower resolution. So in my next test I just cut both in half - scaled to 562x1218 and bitrate at 750kbps and noticed the video also looked great on the iPhone. So 1125x2436 at 750kbps looks bad, but 562x1218 at 750kbps looks great on the same device. To some extent this makes sense to me as you need less bits to fill a smaller screen but what I’m not understanding is how the scaling plays a factor. Shouldn’t it essentially pixelate because the resolution is 1/2 of the iPhone dimensions ? And at a higher level, is there a somewhat concrete way to figure out this optimal resolution / bitrate balance given the dimensions of a device ? We want to most modern smartphones (iPhone 6 and later, Samsung Galaxy, etc.) so we need to be prepared for a range of dimensions (aspect ratios 9:16 or 6:13).

• Creating iPhone compatible video with ffmpeg from an image and MP3 file

  22 février 2020, par Gracie

  I have the following command that I have used to create an MP4 video file from an image and an MP3 file, it plays fine in a Chrome browser on desktop and on an Android phone - but it doesn’t work on an iPhone 10. Do I need some extra codec or setting to make this compatible for iPhone ? Should I be converting this into a MPEG file instead for wider compatibility ?

  ffmpeg -loop 1 -i 6f4aa5dfefc4dd32186f41315ad9d1e2-0.png -i "music.mp3" -c:v libx264 -tune stillimage -c:a aac -b:a 192k -pix_fmt yuv420p -shortest aa-image0.mp4

  Here are the ffprobe details for the input MP3 file used to create the MP4 video and also the ffprobe for that output file :

  Input #0, wav, from 'download0.mp3':
  
    Duration: 00:00:35.94, bitrate: 384 kb/s
  
      Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 24000 Hz, 1 channels, s16, 384 kb/s

  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'aa-image0.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      encoder         : Lavf58.22.100
  
    Duration: 00:00:38.76, start: 0.000000, bitrate: 505 kb/s
  
      Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 2664x1498 [SAR 1:1 DAR 1332:749], 367 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
  
      Metadata:
  
        handler_name    : VideoHandler
  
      Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, mono, fltp, 138 kb/s (default)
  
      Metadata:
  
        handler_name    : SoundHandler

  The video seems to play on the iPhone, but the audio seems to start/stop constantly. Like it is a streaming issue (even though it is not). Maybe an MP3 encoding issue when I created the video ?

  Here are the test files I have used and created (any iPhone users will likely find the MP4 will not play the audio in the video properly) :

  https://ffmpeg-iphone-issue.netlify.com/tesla.jpg

  https://ffmpeg-iphone-issue.netlify.com/tesla.mp3

  https://ffmpeg-iphone-issue.netlify.com/tesla.mp4 (OUTPUT - Created from the 2 files above)

  ---

  In summary, two FFmpeg commands are required :

  1) Used to create iPhone/iOS compatible videos in FFmpeg from an image and MP3 (A slight modification to the command at the top of the page)

  and

  2) An FFmpeg command that could be used to fix or re-encode the video above so that it works on iPhone (A new command incorporating the parts so it works with iPhone and then to rebuild and fix the "broken" video. In a similar fashion to this video where he fixes a broken video https://www.youtube.com/watch?v=2FhmbKKh6mc [command in Youtube description])

• Converting Quicktime (.mov ) from iPhone to mp4

  24 mars 2020, par user3094755

  On iPhones running iOS 11, if a video is pre-recorded and uploaded I get the following errors :- ( ie, the video is recoded on the iPhone and then uploaded as an attachment ).

  $ ./ffmpeg -i .mov -vcodec h264 -acodec mp4 test-output.mp4
  
  FFmpeg version CVS, Copyright (c) 2000-2004 Fabrice Bellard
  
  Mac OSX universal build for ffmpegX
  
    configuration:  --enable-memalign-hack --enable-mp3lame --enable-gpl --disable-vhook --disable-ffplay --disable-ffserver --enable-a52 --enable-xvid --enable-faac --enable-faad --enable-amr_nb --enable-amr_wb --enable-pthreads --enable-x264 
  
    libavutil version: 49.0.0
  
    libavcodec version: 51.9.0
  
    libavformat version: 50.4.0
  
    built on Apr 15 2006 04:58:19, gcc: 4.0.1 (Apple Computer, Inc. build 5250)
  
  [mov,mp4,m4a,3gp,3g2,mj2 @ 0x5597b8]mov: header not found !!! (err:0, moov:0, mdat:0) pos:3189455560
  
  .mov: Error while opening file
  
  $

  If the video is recorded and then transferred to a Desktop uploaded and then converted it works OK.

  If I use a ‘live’ recording then all is OK.

  I found this…

  https://www.howtogeek.com/327689/how-to-make-your-iphone-use-jpg-and-mp4-files-instead-of-heif-and-hevc/

  Which seems to suggest iOS 11 will use different formats, but this appears to make no difference whatever the settings are for ‘High Efficiency / Most Compatible’.

  Any ideas ?