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• react native app doesn't load my video which is made by ffmpeg

  10 mars 2023, par yabbee

  I'm working on react native expo project and using expo-av to play video.I'm experimenting on my iphone and it's working almost fine. I copy and paste the sample code on expo av doc and Big Buck Bunny video is loaded successfully and able to play. But, there is a video that can't be played on my app. I have a video which is stored on s3 server. This is the mp4 video made by ffmpeg command on my computer and manually uploaded it on s3. I can download it and play on my machine. But when I try to load that video on my expo app, the video doesn't show up on the component at all. I write video source correctly including https:// but doesn't show up anything. How can i solve this problem ? I'm using expo 48.0.0 , expo-av 13.2.1 and expo-dev-client 2.1.5 now.

  


  Here is the ffmpeg code that I've used to make video. As you can see, I'm making a retro video by overlaying grain effect mp4 video which I downloaded.

  


  ffmpeg -i /Users/yosuke/Desktop/ffmpeg_playground/effects/grainAndFlash.mp4 -i 
{inputFilePath} -filter_complex "[0:a][1:a]amerge[mixedAudio];
[0]format=rgba,colorchannelmixer=aa=0.25[fg];[1][fg]overlay[out];
[out]trim=0:32,setpts=PTS-STARTPTS[video]" -map "[video]" -map "[mixedAudio]" -
pix_fmt yuv420p -c:v libx264 -crf 18 -shortest {outputFilePath}


  


  Here is the Expo app code

  


  import React, { useState, useEffect, useContext, useRef } from &#x27;react&#x27;;&#xA;import { View, Text, ScrollView, TouchableOpacity, Dimensions } from &#x27;react-native&#x27;;&#xA;&#xA;const Container = () => {&#xA;    const vidRef = useRef(null);&#xA;return (&#xA;    <scrollview style="{{" 1="1">&#xA;      &#xA;    </scrollview>&#xA;  );&#xA;};&#xA;&#xA;export default Container;&#xA;

  


• Rails ActionController::Live - Sends everything at once instead of async

  28 janvier 2016, par Michael B

  I have an issue with rails ActionController::Live

  In the end I want to show the progress of FFMPEG to the user, but for now I want to get this minimal example running :

  Rails media_controller.rb :

  class MediaController < ApplicationController
  
    include ActionController::Live
  
  
  
    def stream
  
      puts "stream function loaded"
  
  
  
        response.headers['Content-Type'] = 'text/event-stream'
  
        i = 0
  
        begin
  
          response.stream.write "data: 1\n\n"
  
          sleep 0.5
  
          i += 1
  
          puts "response... data: " + i.to_s
  
        end while i < 10
  
      response.stream.close
  
    end
  
  end

  Javascript :

  source = new EventSource("/test/0");
  
  source.addEventListener("message", function(response) {
  
    // Do something with response.data
  
    console.log('I have received a response from the server: ' + response);
  
  }, false);

  When I navigate to the site, there are no JavaScript Errors showing. As soon as I navigate to the site, the "stream"-Action of the MediaController gets successfully called. I can verify this, by looking at the Server-Console. It gives me the following output. After every response line, there is a 500ms delay, like expected :

  stream function loaded
  
  response... data: 1
  
  response... data: 2
  
  response... data: 3
  
  response... data: 4
  
  response... data: 5
  
  response... data: 6
  
  response... data: 7
  
  response... data: 8
  
  response... data: 9
  
  response... data: 10
  
  Completed 200 OK in 5005ms (ActiveRecord: 0.8ms)

  On the JavaScript Side, it gives me the following Output :

  (10x) I have received a response from the server: [object MessageEvent]

  But the problem is here, that it sends all these 10 Messages from the server after 5 seconds at the same time ! The expected behavior however is, that it should send me 1 message every 0.5 seconds !

  So what am I doing wrong here ? Where is the error ?

  

• Fast movie creation using MATLAB and ffmpeg

  24 février 2018, par hyiltiz

  I have some time series data that I would like to create into movies. The data could be 2D (about 500x10000) or 3D (500x500x10000). For 2D data, the movie frames are simply line plot using plot, and for 3D data, we can use surf, imagesc, contour etc. Then we create a video file using these frames in MATLAB, then compress the video file using ffmpeg.

  To do it fast, one would try not to render all the images to display, nor save the data to disk then read it back again during the process. Usually, one would use getframe or VideoWriter to create movie in MATLAB, but they seem to easily get tricky if one tries not to display the figures to screen. Some even suggest plotting in hidden figures, then saving them as images to disk as .png files, then compress them using ffmpeg (e.g. with x265 encoder into .mp4). However, saving the output of imagesc in my iMac took 3.5s the first time, then 0.5s after. I also find it not fast enough to save so many files to disk only to ask ffmpeg to read them again. One could hardcopy the data as this suggests, but I am not sure whether it works regardless of the plotting method (e.g. plot, surf etc.), and how one would transfer data over to ffmpeg with minimal disk access.

  This is similiar to this, but immovie is too slow. This post 3 is similar, but advocates writing images to disk then reading them (slow IO).