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• h.264 video in mp4 container jumps when played in VLC

  30 avril 2013, par Jayanth Nayak

  I have H.264 video and AAC audio generated in Andriod phone recieved wirelessly using SIP protocol and muxed using FFMPEG APIs, The generated mp4 when played through VLC or other player is never in Sync.
  when I see the time bar of Video, it skips after a certain duration.

  For example :
  in a video of 20s, the time bar seeks upto 14s properly, then it jumps to 18s and finishes at 20. The audio plays properly.

  I have following questions :

  1. Is PTS DTS calculations really required for muxing WITHOUT Encoding ? :

  we used

  PTS = (90000 * (1/FPS) * FrameNumber) - although this did not work :(

  currently FFMPEG is taking care of it internally.

  ---

  1. Why the video jumps ? is it because of less number of frames or wrong PTS values or something else ?

  ---

  1. For the following cases although There is jump, I am getting a good AV sync
     -15,20,25 FPS qCIF & AAC Audio

     But for 15 & 20 FPS of qVGA & VGA the audio lags by 0.5 seconds and for 25 FPS, the Video is just playing fast.
     thus why is there a delay for qVGA and VGA but not present for qCIF ? any dependency of Resolution on Time Stamp (PTS) calculation ??

     Analysis of 25 FPS Video showed that there are enough number of frames for 10s but the total time for the video shown by VLC is 14s. Why is this so ? and again, this video also jumps from 9s to 13s.

• Grey screen issue after recovered video with ffmpeg

  10 mars 2023, par Mark

  After recovered ".mp4" videos from mobile phone, some videos were corrupt. I used the FFMPEG method to fix the videos.
Some CMD commands below ;

  


  First Code: recover_mp4.exe good.mp4 --analyze

Second: recover_mp4.exe bad.mp4 recovered.h264 recovered.aac

Third: ffmpeg.exe -r 30 -i recovered.h264 -i recovered.aac -bsf:a aac_adtstoasc -c:v copy -c:a copy recovered.mp4

Alternate code: ffmpeg -i recovered.h264 -pix_fmt yuv420p -crf 18 result.mp4


  


  Some videos have been improved after using the above codes. Some videos work fine. On the other hand some videos work in video players, but images are only gray or green screen or a mix of both. In short, some videos do not work properly.

  


  Below I am sharing a screenshot from the video that is not working properly.

  


  greyscreenphotoexample

  


  Is it possible to fix the above errors ? Is there any other code or method I should use ? How can I handle the gray screen problems in the video ?

  


  Note : I have used all versions of FFMPEG and Recover_mp4.exe.

  


• How to set specific minimal bitrate of video with light_compressor package in Flutter ?

  21 juin 2023, par Giant Brain

  I tried using flutter's light_compressor package to compress a video I shot with my phone or downloaded from YouTube.

  


  I refer to the article below.
https://morioh.com/p/ac6f0d2c176b
In this article, the minimum bit rate can be set and the default value is 2mbps.

  


  However, in the sample code, only the flag isMinBitrateCheckEnabled exists, and there is no parameter to set a specific bit rate.

  


  How do I compress the video to my desired bitrate ?

  


  Below is a part of the sample code.

  


  import 'package:light_compressor/light_compressor.dart';


final LightCompressor _lightCompressor = LightCompressor();
final dynamic response = await _lightCompressor.compressVideo(
  path: _sourcePath,
  destinationPath: _destinationPath,
  videoQuality: VideoQuality.medium,
  isMinBitrateCheckEnabled: false,
  frameRate: 24 /* or ignore it */);