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• Record D3.js whiteboard animation as mp4 audio and video

  9 août 2015, par Jin Ng

  I have a whiteboard/hand sketching app written with D3.js svg path elements. These elements are grouped into scenes with their own mp3 audio.

  Multiple scenes with their animated svg paths are played according to a timeline, with the audio running perfectly.

  So the end result is like a whiteboard animated movie. This works well within the app. How can i record the whole animation as a mp4 file ?

  I would like to run this entirely on the client side. I have looked at ffmpeg but prefer not to do a desktop install for this web app.

  I looked into using chrome tab extension but it only works on chrome browser.

  What other options do I have ?

• Video recorded from a webcam using FFmpeg is desynchronizing in iOS native player

  11 mars 2021, par Luuudo

  Objective

  


  I am trying to record a video (duration ≈ 1min to 4hours) from a webcam plugged into a PC. Then play just after the end of the recording the video on an Ipad connected to the same network as the PC.

  


  To do this I'm trying to record the video using ffmpeg (the detailed command I use is below). Then I serve the video that's on the PC to the Ipad via a Java server (The server works well with other videos so I don't think the problem is here).

  


  Problem

  


  When I play the video on the IPad native player, for example in Safari, the sound is going faster than the video and therefore it's desynchronizing from the video. If I request a certain time the video and audio re-sync then the audio is desynchronizing again while playing.

  


  

  • The video when played on VLC on the PC or on Firefox by requesting the server is well synced.

  


  • Another video (I downloaded this one to test) played on the Ipad from the server stay synced.

  


  


  It is only with the combination of a video record by myself using FFmpeg played in the iOS native player that I can observe the desynchronization.

  


  FFmpeg command

  


  I use FFmpeg to record the video from the webcam and save it into a file format readable on iOS.

  


  ffmpeg -y -f avfoundation -framerate 25 -pixel_format nv12 -video_size 1280x720 -i "0:0" -r 25 out.mp4


  


  The resulting recorded file info according to ffmpeg is below :

  


  > ffmpeg -i out.mp4
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'out.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.45.100
  Duration: 00:00:33.76, start: 0.000000, bitrate: 1510 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1280x720, 1440 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, 61 kb/s (default)
    Metadata:
      handler_name    : SoundHandler


  


  Compatible video formats from TV and Video iPad Pro specs

  


  


  Video formats supported : H.264 video up to 4K, 30 frames per second, High Profile level 4.2 with AAC‑LC audio up to 160 Kbps, 48kHz, stereo audio or Dolby Audio up to 1008 Kbps, 48kHz, stereo or multichannel audio, in .m4v, .mp4, and .mov file formats ; MPEG‑4 video up to 2.5 Mbps, 640 by 480 pixels, 30 frames per second, Simple Profile with AAC‑LC audio up to 160 Kbps per channel, 48kHz, stereo audio or Dolby Audio up to 1008 Kbps, 48kHz, stereo or multichannel audio, in .m4v, .mp4, and .mov file formats ; Motion JPEG (M‑JPEG) up to 35 Mbps, 1280 by 720 pixels, 30 frames per second, audio in ulaw, PCM stereo audio in .avi file format

  


  


  I don't see what codecs or profiles I don't respect ?

  


  ps : I write PC but I'm currently trying this on a Mac. Eventually, I want to be able to do it also on Linux or even Windows. It looks like I just have to change the input devices to do that, which is avfoundation for MacOS.

  


• How can I record audio from output device using ffmpeg ?

  17 mai 2020, par Nimeth

  I'm building an app (Android and iOS) that user could sing MV Karaoke over HLS video streaming. To produce a final recording for a user, I use ffmpeg to mix the audio stream taken directly from the song with user's recorded vocal and video. But the big challenge is when there are silence periods during recording due to low internet bandwidth, there would be a significant lag time in the final mixed output which is not acceptable for users. How can I use ffmpeg to live record audio being played by another player and use it to mix with user's vocal ?