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• FFmpeg "Non-monotonous DTS in output stream" error when processing video from Safari's MediaRecorder

  17 juillet 2024, par Hackermon

  I'm recording a video stream in Safari with MediaRecorder, then sending it to a remote server which then uses ffmpeg to reencode the video. When reencoding with FFmpeg, I get a lot of warnings and the final video is broken, frame are glitching and out of sync but the audio sounds fine.

  


  Here's my MediaRecorder script :

  


  const camera = await navigator.mediaDevices.getUserMedia({ audio: true, video: true });
const recorder = new MediaRecorder(camera, {
        mimeType: 'video/mp4', // Safari only supports MP4
        bitsPerSecond: 1_000_000,
});

recorder.ondataavailable = async ({ data: blob }) => {
        // open contents in new tab
        var fileURL = URL.createObjectURL(file);
         window.open(fileURL, '_blank');
};

recorder.start();
setTimeout(() => recorder.stop(), 5000);


  


  I download the video blob from Safari and use this command to reencode it :

  


  ffmpeg -i ./blob.mp4 -preset ultrafast -strict -2 -threads 10 -c copy ./output.mp4


  


  Logs :

  


  ffmpeg version 4.2.7-0ubuntu0.1 Copyright (c) 2000-2022 the FFmpeg developers
  built with gcc 9 (Ubuntu 9.4.0-1ubuntu1~20.04.1)
  configuration: --prefix=/usr --extra-version=0ubuntu0.1 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-avresample --disable-filter=resample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-nvenc --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
  libavutil      56. 31.100 / 56. 31.100
  libavcodec     58. 54.100 / 58. 54.100
  libavformat    58. 29.100 / 58. 29.100
  libavdevice    58.  8.100 / 58.  8.100
  libavfilter     7. 57.100 /  7. 57.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  5.100 /  5.  5.100
  libswresample   3.  5.100 /  3.  5.100
  libpostproc    55.  5.100 / 55.  5.100
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x559826616000] DTS 29 < 313 out of order
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from './chunk1.mp4':
  Metadata:
    major_brand     : iso5
    minor_version   : 1
    compatible_brands: isomiso5hlsf
    creation_time   : 2024-07-17T14:30:47.000000Z
  Duration: 00:00:01.00, start: 0.000000, bitrate: 3937 kb/s
    Stream #0:0(und): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p(progressive), 640x480 [SAR 1:1 DAR 4:3], 6218 kb/s, 33.36 fps, 600 tbr, 600 tbn, 1200 tbc (default)
    Metadata:
      creation_time   : 2024-07-17T14:30:47.000000Z
      handler_name    : Core Media Video
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 420 kb/s (default)
    Metadata:
      creation_time   : 2024-07-17T14:30:47.000000Z
      handler_name    : Core Media Audio
File './safari3.mp4' already exists. Overwrite ? [y/N] Output #0, mp4, to './safari3.mp4':
  Metadata:
    major_brand     : iso5
    minor_version   : 1
    compatible_brands: isomiso5hlsf
    encoder         : Lavf58.29.100
    Stream #0:0(und): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p(progressive), 640x480 [SAR 1:1 DAR 4:3], q=2-31, 6218 kb/s, 33.36 fps, 600 tbr, 19200 tbn, 600 tbc (default)
    Metadata:
      creation_time   : 2024-07-17T14:30:47.000000Z
      handler_name    : Core Media Video
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 420 kb/s (default)
    Metadata:
      creation_time   : 2024-07-17T14:30:47.000000Z
      handler_name    : Core Media Audio
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
[mp4 @ 0x559826644340] Non-monotonous DTS in output stream 0:0; previous: 10016, current: 928; changing to 10017. This may result in incorrect timestamps in the output file.
[mp4 @ 0x559826644340] Non-monotonous DTS in output stream 0:0; previous: 10017, current: 1568; changing to 10018. This may result in incorrect timestamps in the output file.
[mp4 @ 0x559826644340] Non-monotonous DTS in output stream 0:0; previous: 10018, current: 2208; changing to 10019. This may result in incorrect timestamps in the output file.
...x100
frame=  126 fps=0.0 q=-1.0 Lsize=     479kB time=00:00:00.97 bitrate=4026.2kbits/s speed= 130x    
video:425kB audio:51kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.652696%


  


  Not sure what's happening or how to fix it. This issue only happens in Safari, videos from Chrome are perfectly fine.

  


  I've tried various flags :

  


  -fflags +igndts
-bsf:a aac_adtstoasc
-c:v libvpx-vp9 -c:a libopus
etc


  


  None of them seem to fix the issue.

  


• ffmpeg does not respect the -t option and keeps recording [closed]

  21 juillet 2024, par Naman Muley

  The command I use is :

  


   ffmpeg -f avfoundation -framerate 30 -i "2:0" -vcodec libx264 -pix_fmt yuv420p -acodec aac -strict experimental -t 10 ./recordings/tmp.mp4


  


  With the above command, I expect the recording output to stop after 10 seconds. But the ffmpeg command keeps running and does not stop.
Feels like I am missing something basic but I have now spent 3 hours debugging and cannot figure out why.

  


  Usecase :
I need to record my screen's video as well as audio for a specifiable amount of time.

  


  According to the manual, putting -t before -i limits the input recording and putting it after -i limits the output recording. I believe after the -i is the correct way to go.

  


  Output of list devices :

  


   ffmpeg -v verbose -f avfoundation -list_devices true -i ""
ffmpeg version 7.0.1 Copyright (c) 2000-2024 the FFmpeg developers
  built with Apple clang version 15.0.0 (clang-1500.1.0.2.5)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/7.0.1 --enable-shared --enable-pthreads --enable-version3 --cc=clang --host-cflags= --host-ldflags='-Wl,-ld_classic' --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libaribb24 --enable-libbluray --enable-libdav1d --enable-libharfbuzz --enable-libjxl --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librist --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libssh --enable-libsvtav1 --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvmaf --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox --enable-audiotoolbox
  libavutil      59.  8.100 / 59.  8.100
  libavcodec     61.  3.100 / 61.  3.100
  libavformat    61.  1.100 / 61.  1.100
  libavdevice    61.  1.100 / 61.  1.100
  libavfilter    10.  1.100 / 10.  1.100
  libswscale      8.  1.100 /  8.  1.100
  libswresample   5.  1.100 /  5.  1.100
  libpostproc    58.  1.100 / 58.  1.100
[AVFoundation indev @ 0x7fdc48f047c0] AVFoundation video devices:
[AVFoundation indev @ 0x7fdc48f047c0] [0] FaceTime HD Camera (Built-in)
[AVFoundation indev @ 0x7fdc48f047c0] [1] Screwdriver Desk View Camera
[AVFoundation indev @ 0x7fdc48f047c0] [2] Capture screen 0
[AVFoundation indev @ 0x7fdc48f047c0] [3] Capture screen 1
[AVFoundation indev @ 0x7fdc48f047c0] AVFoundation audio devices:
[AVFoundation indev @ 0x7fdc48f047c0] [0] Built-in Microphone
[AVFoundation indev @ 0x7fdc48f047c0] [1] Screwdriver Microphone
[in#0 @ 0x7fdc49904080] Error opening input: Input/output error
Error opening input file .
Error opening input files: Input/output error


  


  

  • I tried using different codecs and pix_fmt options.

  


  • Tried moving the -t before the -i option and after. no change.

  


  


  Works with only audio input :
The below command that records only the audio works out just fine.

  


  ffmpeg -f avfoundation -i ":0" -acodec libmp3lame -t 10 ./recordings/tmp.mp3


  


• Understanding User Flow : Eight Practical Examples for Better UX

  4 octobre 2024, par Daniel Crough — Analytics Tips, UX

  Imagine trying to cook a complex dish without a recipe. You might have all the ingredients, but without a clear sequence of steps, you’re likely to end up with a mess rather than a masterpiece. Similarly, designing a website without understanding user flow is a recipe for confusion and lost conversions.

  User flows—the paths visitors take through your site—are the recipes for digital success. They provide a clear sequence of steps that guide users towards their goals, whether that’s making a purchase, signing up for a newsletter, or finding information. By understanding and optimising these flows, you can create a website that’s not just functional, but delightfully intuitive.

  In this article, we’ll explore seven practical user flow examples and show you how to apply these insights using web analytics tools. Whether you’re new to user experience (UX) design or a seasoned professional, you’ll find valuable takeaways to enhance your digital strategy.

  Read More