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• How to make WebM screen recording chunks independently processable for audio with FFmpeg ?

  3 décembre 2024, par Dinesh Kumar

  I am streaming screen recordings from the browser into 5-second WebM chunks using the MediaRecorder API. The first chunk (root chunk) is independently processable because it contains the necessary EBML headers and metadata. However, subsequent chunks are not independently processable, as they lack the required metadata, which prevents me from extracting audio independently from them.

  


  I am unable to extract audio independently from the individual chunks using FFmpeg due to missing headers, resulting in errors like EBML header parsing failed. The first chunk works fine on its own, but the subsequent chunks also need to be processed independently for audio extraction.

  


  I am looking for a solution using FFmpeg to fix these chunks so that I can extract audio independently from each chunk.

  


  

  1. Is there a way to repair these chunks post-recording with FFmpeg to include the missing metadata and headers, making them independently processable for audio extraction ?

  


  2. Can FFmpeg reinitialize the EBML headers in each chunk, or is there a command that can add the metadata from the first chunk to subsequent chunks to allow for independent audio extraction ?

  


  


  Additionally, should I consider any changes in the MediaRecorder API to ensure that the chunks are properly formatted for independent processing ? The goal is to make each WebM chunk fully independent, allowing me to extract audio independently from each chunk.

  


• FFMPEG video editing application. Need time and date stamp burned into video

  11 mai 2022, par Jacob

  I am developing an application for video editing. The main component of this application is to produce a single video file from several video files captured from a camcorder with the time and date stamp displayed on the final rendered video, much like the final product from a security camera. I have figured out, by using FFMPEG, how to burn the date and time into the video with a .SRT file as well as with DrawText like the following :

  


  ffmpeg -y -i video.mp4 -vf “drawtext=fontfile=roboto.ttf:fontsize=12:fontcolor=yellow:text='%{pts\:localtime\:1575526882\:%A, %d, %B %Y %I\\\:%M\\\:%S %p}'" -preset ultrafast -f mp4 output_new.mp4    


  


  I would rather use the DrawText method so the user does not have to wait longer while creating the .SRT files. I am new to FFMPEG and I find their documentation very confusing. I guess I am hoping there is someone out there who has experience with it.

  


  Everything seems to work when I pass in the date created meta data from the video file and drawtext just does its thing. The problem is my application allows for editing of the video. I do this, for lack of better solution, by allowing the user to select beginning and ending frames they do not want, from the UI and then the code simply deletes the frames from the directory where they were split and saved. I then use FFMPEG to iterate through the directory and combine the remaining frames to make a video file.

  


  This approach starts the time and date from the date created metadata ; however, cutting the frames out of the video will make the DT stamp inaccurate, due to the missing frames.

  


  Is there any way to tell FFMPEG to burn in the date and time from date/time retrieved from each individual frame ? I appreciate any advice that you may have.

  


• What does FFmpeg expect me to send to the first rawvideo input pipe ?

  23 octobre 2023, par Somebody

  I'm using two named pipes, in order :

  


  

  1. video_pipe


     -f rawvideo
-video_size 1x1
-pix_fmt gray
-r 1


     


  


  2. audio_pipe


     -f s16le
-ar 32000
-channels 1


     


  


  


  I thought FFmpeg needed to read individual frames from a rawvideo pipe but I must be mistaken cause it doesn't start reading from the second pipe until I feed 11 bytes to the first pipe although, in the example given, a grayscale frame of one pixel is exactly one byte. I have experimenting by increasing video_size and here's the table I could infer :

  


  





  


  


  


  


  



  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  


  Actual frame size in bytes	Bytes needed to be sent before to move on
  1	11
  2	17
  3	25
  4	33
  5	41
  6	49

  


  


  I can't just send multiple frames as I want to output a 1 second video.
I tested most of the parameters in this page : https://github.com/FFmpeg/FFmpeg/blob/ff5a3575fec2d49d5fae4ec1198a939e203314db/libavformat/options_table.h
but none of them solved it. (I also used "-re" with no luck).

  


  This is an example command in case you want to reproduce the issue :
ffmpeg -y -re -f rawvideo -video_size 1x1 -pixel_format gray -framerate 1 -i \\.\pipe\video_pipe -f s16le -ar 32000 -channels 1 -i \\.\pipe\audio_pipe -map 0:v:0 -map 1:a:0 out.mp4

  


  Any idea of how I could send the exact frame bytes amount instead of being forced to send way more bytes ?