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• FFmpeg decoding .mp4 video file

  3 mars 2016, par Sir DrinksCoffeeALot

  I’m working on a project that needs to open .mp4 file format, read it’s frames 1 by 1, decode them and encode them with better type of lossless compression and save them into a file.

  Please correct me if i’m wrong with order of doing things, because i’m not 100% sure how this particular thing should be done. From my understanding it should go like this :

  1. Open input .mp4 file
  
  2. Find stream info -> find video stream index
  
  3. Copy codec pointer of found video stream index into AVCodecContext type pointer
  
  4. Find decoder -> allocate codec context -> open codec
  
  5. Read frame by frame -> decode the frame -> encode the frame -> save it into a file

  So far i encountered couple of problems. For example, if i want to save a frame using av_interleaved_write_frame() function, i can’t open input .mp4 file using avformat_open_input() since it’s gonna populate filename part of the AVFormatContext structure with input file name and therefore i can’t "write" into that file. I’ve tried different solution using av_guess_format() but when i dump format using dump_format() i get nothing so i can’t find stream information about which codec is it using.

  So if anyone have any suggestions, i would really appreciate them. Thank you in advance.

• How can combine two separate scripts being piped together to make one script instead of two ?

  27 mars 2016, par user556068

  For the past couple hours I’ve been banging my head against the wall trying to figure out something I thought would be simple. Maybe it is but it’s beyond me at the moment. So I have now two scripts. Originallly they were part of the same but I could never make it work how it should. So the first part uses curl to download a file from a site. Then using grep and sedto filter out the text I need which is then put into a plain text file as a long list of website urls ; one per line. The last part of the 1st script calls on youtube -dl to read the batch file in order to obtain the web addresses where the actual content is located. I hope that makes sense.

  youtube-dl reads the batch file and outputs a new list urls into the terminal. This second list is not saved to file because it doesn’t need to be. These urls change from day to day or hour to hour. Using the read command, these urls are then passed to ffmpeg using a predetermined set of arguments for the input and output. Ffmpeg is executed on every url it receives and runs quietly in the background.

  The first paragraph describes script1.sh and paragraph 2 obviously describes script2.sh. When I pipe them together like script1.sh | script2.sh it works better than I ever thought possible. Maybe i’m nitpicking at this point but the idea is to have 1 unified script. For the moment I have simplified it by adding an alias to my .bash_profile.

  Here are the last two commands of script1.

  sed 's/\"\,/\//g' > "$HOME/file2.txt";
  
  cat $HOME/file2.txt | youtube-dl --ignore-config -iga -

  The trailing - allows youtube-dl to read from stdin.

  The second part of the script ; what I’m calling script2 at this point begins with

  while read -r input
  
  do
  
  ffmpeg [arg] [input] [arg2] [output]

  What am i not seeing that is causing the script to hang when the two halves are combined yet work perfectly if one is piped into the other ?

• Nodejs - Using ffmpeg with video thumbnails

  8 mars 2016, par RunningFromShia

  I am pretty much lost within the concept of ffmpeg and nodejs. ffmpeg is supposed to do important conversion work, that I get, but every time I try to implement a nodejs package with ffmpeg it just fails. I will give an example :

  using this for example in my app :
  https://www.npmjs.com/package/video-thumb

  my app.js :

  var express = require('express');
  
  var app = express();    
  
  
  
  var thumbler = require('video-thumb');
  
  
  
  thumbler.extract('http://www.w3schools.com/html/mov_bbb.mp4', 'snapshot.png', '00:00:1', '200x125', function(){
  
  
  
      console.log('snapshot saved to snapshot.png (200x125) with a frame at 00:00:1');
  
  
  
  });
  
  
  
  var port = process.env.PORT || 1337;
  
  
  
  app.listen(port);  

  Basically, I’ve tried a couple of nodejs packages that turn a snapshot out of a given video, and then save it to my server. each attempt failed. they all use ffmpeg. the above is just one of them.

  Now, I put a ffmpeg.exe in my root folder, I am just not sure where it’s supposed to be or how to use it with node. Needless to say, the above example doesn’t do anything. Tutorials online only show how to convert a certain video to a certain format in windows using ffmpeg, there is nothing about nodejs.
  I’d like some guidance here, thank you for your time.