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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).

• How to export audio from a iPhone video file with FFmpeg ?

  11 janvier 2020, par DanScripter

  UPDATE 1 the problem resides in the input read-stream. (check below)

  I am using fluent-ffmpeg (version : 2.1.2) to get a .mp3 file out of a video file that I input as a stream .createReadStream(). I output the file as a .pipe to a remoteWriteStream.

  ffmpeg -i pipe:0 -vn -f mp3 -acodec mp3 -movflags frag_keyframe+empty_moov pipe:1

  This works fine with .mp4, .webm and .mov (codec : prores) files.

  But it somehow does not want to work with a .mov out of an iPhone 11. FFmpeg is not giving me any error when running above code. It creates the .mp3 file but the size is just 152 B and it is not playable.

  I ffprobed the iPhone .mov files it returns this :

  "{ streams: 
  
     [ { index: 0,
  
         codec_name: 'hevc',
  
         codec_long_name: 'H.265 / HEVC (High Efficiency Video Coding)',
  
         profile: 'Main',
  
         codec_type: 'video',
  
         codec_time_base: '1111/33300',
  
         codec_tag_string: 'hvc1',
  
         codec_tag: '0x31637668',
  
         width: 1920,
  
         height: 1080,
  
         coded_width: 1920,
  
         coded_height: 1088,
  
         has_b_frames: 2,
  
         sample_aspect_ratio: '0:1',
  
         display_aspect_ratio: '0:1',
  
         pix_fmt: 'yuv420p',
  
         level: 120,
  
         color_range: 'tv',
  
         color_space: 'bt709',
  
         color_transfer: 'bt709',
  
         color_primaries: 'bt709',
  
         chroma_location: 'unspecified',
  
         field_order: 'unknown',
  
         timecode: 'N/A',
  
         refs: 1,
  
         id: 'N/A',
  
         r_frame_rate: '30000/1001',
  
         avg_frame_rate: '33300/1111',
  
         time_base: '1/600',
  
         start_pts: 'N/A',
  
         start_time: 'N/A',
  
         duration_ts: 6666,
  
         duration: 11.11,
  
         bit_rate: 7611708,
  
         max_bit_rate: 'N/A',
  
         bits_per_raw_sample: 'N/A',
  
         nb_frames: 333,
  
         nb_read_frames: 'N/A',
  
         nb_read_packets: 'N/A',
  
         tags: [Object],
  
         disposition: [Object] },
  
       { index: 1,
  
         codec_name: 'aac',
  
         codec_long_name: 'AAC (Advanced Audio Coding)',
  
         profile: 'unknown',
  
         codec_type: 'audio',
  
         codec_time_base: '1/44100',
  
         codec_tag_string: 'mp4a',
  
         codec_tag: '0x6134706d',
  
         sample_fmt: 'fltp',
  
         sample_rate: 44100,
  
         channels: 2,
  
         channel_layout: 'stereo',
  
         bits_per_sample: 0,
  
         id: 'N/A',
  
         r_frame_rate: '0/0',
  
         avg_frame_rate: '0/0',
  
         time_base: '1/44100',
  
         start_pts: 'N/A',
  
         start_time: 'N/A',
  
         duration_ts: 489951,
  
         duration: 11.11,
  
         bit_rate: 135091,
  
         max_bit_rate: 192000,
  
         bits_per_raw_sample: 'N/A',
  
         nb_frames: 481,
  
         nb_read_frames: 'N/A',
  
         nb_read_packets: 'N/A',
  
         tags: [Object],
  
         disposition: [Object] },
  
       { index: 2,
  
         codec_name: 'unknown',
  
         codec_long_name: 'unknown',
  
         profile: 'unknown',
  
         codec_type: 'data',
  
         codec_tag_string: 'mebx',
  
         codec_tag: '0x7862656d',
  
         id: 'N/A',
  
         r_frame_rate: '0/0',
  
         avg_frame_rate: '0/0',
  
         time_base: '1/600',
  
         start_pts: 'N/A',
  
         start_time: 'N/A',
  
         duration_ts: 6666,
  
         duration: 11.11,
  
         bit_rate: 2670,
  
         max_bit_rate: 'N/A',
  
         bits_per_raw_sample: 'N/A',
  
         nb_frames: 38,
  
         nb_read_frames: 'N/A',
  
         nb_read_packets: 'N/A',
  
         tags: [Object],
  
         disposition: [Object] },
  
       { index: 3,
  
         codec_name: 'unknown',
  
         codec_long_name: 'unknown',
  
         profile: 'unknown',
  
         codec_type: 'data',
  
         codec_tag_string: 'mebx',
  
         codec_tag: '0x7862656d',
  
         id: 'N/A',
  
         r_frame_rate: '0/0',
  
         avg_frame_rate: '0/0',
  
         time_base: '1/600',
  
         start_pts: 'N/A',
  
         start_time: 'N/A',
  
         duration_ts: 6666,
  
         duration: 11.11,
  
         bit_rate: 7,
  
         max_bit_rate: 'N/A',
  
         bits_per_raw_sample: 'N/A',
  
         nb_frames: 1,
  
         nb_read_frames: 'N/A',
  
         nb_read_packets: 'N/A',
  
         tags: [Object],
  
         disposition: [Object] },
  
       { index: 4,
  
         codec_name: 'unknown',
  
         codec_long_name: 'unknown',
  
         profile: 'unknown',
  
         codec_type: 'data',
  
         codec_tag_string: 'mebx',
  
         codec_tag: '0x7862656d',
  
         id: 'N/A',
  
         r_frame_rate: '0/0',
  
         avg_frame_rate: '0/0',
  
         time_base: '1/600',
  
         start_pts: 'N/A',
  
         start_time: 'N/A',
  
         duration_ts: 6666,
  
         duration: 11.11,
  
         bit_rate: 18117,
  
         max_bit_rate: 'N/A',
  
         bits_per_raw_sample: 'N/A',
  
         nb_frames: 333,
  
         nb_read_frames: 'N/A',
  
         nb_read_packets: 'N/A',
  
         tags: [Object],
  
         disposition: [Object] } ],
  
    format: 
  
     { filename: 'pipe:0',
  
       nb_streams: 5,
  
       nb_programs: 0,
  
       format_name: 'mov,mp4,m4a,3gp,3g2,mj2',
  
       format_long_name: 'QuickTime / MOV',
  
       start_time: 'N/A',
  
       duration: 11.11,
  
       size: 'N/A',
  
       bit_rate: 'N/A',
  
       probe_score: 100,
  
       tags: 
  
        { major_brand: 'qt  ',
  
          minor_version: '0',
  
          compatible_brands: 'qt  ',
  
          creation_time: '2020-01-11T12:33:36.000000Z',
  
          'com.apple.quicktime.make': 'Apple',
  
          'com.apple.quicktime.model': 'iPhone 11',
  
          'com.apple.quicktime.software': '13.3',
  
          'com.apple.quicktime.creationdate': '2020-01-11T13:33:36+0100' } },
  
    chapters: [] }" 

  The created .mp3 file results in a undefined.

  I already tried to take the .mov re-encode it to an .mp4 via ffmpeg and then try the above code to get the .mp3 - still does not work.

  Any advice how I can make this work ?

  thanks !

  ---

  UPDATE 1
  The problem resides in the input stream ! When I download the file to the local machine and input it as as a local file, not as a read stream, it works perfectly.

  I am creating the stream from a google cloud bucket like this :

  const myBucket = storage.bucket('myBucket');
  
  const remoteReadStream = myBucket.file(file).createReadStream();

  Since this code is perfectly working with all other codecs, what maybe the issue while creating the read stream from the google cloud from a h265 file ?

• How to deal ffplay being too slow playing iPhone's videos ?

  8 janvier 2020, par Mikhail T.

  Trying to play a 3840x2160 video recorded by an iPhone 7 (@30fps), I get frequent pauses — in the video, music keeps playing.

  



  This happens both in firefox and when ffplay is invoked to play the file directly — from command-line. The CPU is a dual E6700 @3.20GHz — not super fast, but it should be able to play smoothly, shouldn't it ? Video is Intel's "series 4" integrated chipset — again, not a speed-daemon, but it should be adequate... Support for Intel's VA API is included.

  



  I build ffmpeg-4.1 from source using FreeBSD port. As you can see, the port has a maddening amount of options — including several different ones for the 264-codec.

  



  Any suggestions for improving the decoding speed to the point, where it is watchable by a human ? Thank you !