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• Concatenating videos using ffmpeg writes over empty audio stream

  3 avril 2020, par Rutwik Kharkar

  I have 4 movie files that I am trying to overlay and concatenate :

  



  

  1. Intro file with an empty audio channel (generated using lavfi)

  


  2. Main movie file(s) that need to be concatenated and trimmed

  


  3. Watermark that needs to be overlaid on top of 2

  


  4. An outro movie that also has an empty channel.

  


  



  Here is the command I am using to do all this :

  



  ffmpeg -i temp_intro.mp4 -f concat -i tempFile.txt -i scoreboard.mp4 -i temp_outro.mp4 \
-filter_complex "[1]trim=end=24:start=12[s0];[s0]setpts=PTS-STARTPTS[s1];[1]atrim=end=24:start=12[s2];[s2]asetpts=PTS-STARTPTS[s3];\
[s1][s3]concat=a=1:n=1:v=1[s4];\
[2]format=yuva444p[s5];[s5]colorchannelmixer=aa=0.5[s6];\
[s4][s6]overlay=eof_action=repeat:x=(main_w-overlay_w)/2:y=main_h-overlay_h-20[s7];\
[0][s7][3]concat=n=3[s8]" test.mp4


  



  Despite how ugly it looks, it mostly works - except for the audio. The audio starts playing as soon as the intro clip starts. I cannot create an output file with the overlaid movie because I also need to add fade-out and fade-in effects for the intro and outro. I can only re-encode once since I will be doing this over multiple large files every night.

  



  Please suggest how I might be able to fix the audio issue.

  


• ffmpeg video rendering command adding empty audio to end of video

  13 janvier 2020, par Martin

  I have an ffmpeg command which is supposed to take an mp3 file and image file as inputs, and render a music video with the image as the background and the video length is the exact length of the mp3 audio file input.

  I was using this command :

  ffmpeg -loop 1 -framerate 2 -i "front.jpg" -i "audioInput.mp3" -vf "scale=2*trunc(iw/2):2*trunc(ih/2),setsar=1,format=yuv420p" -c:v libx264 -preset medium -tune stillimage -crf 18 -c:a aac -b:a 320k -shortest -vf scale=1920:1080 -pix_fmt yuv420p "videoOutput.mp4"

  But the problem was that my audioInput.mp3 file is 1 minute 12 seconds long, and my output video was 1 minute 39 seconds, with an added couple seconds of silence at the end of the video.

  I asked a question on stackoverflow and it was closed/linked to this question. The accepted answer says that this command would not add extra seconds onto the end of the video :

  ffmpeg -y -loop 1 -framerate 2 -i "front.jpg" -i "maintheme.mp3" -c:v libx264 -tune stillimage -c:a aac -b:a 320k -pix_fmt yuv420p -shortest -fflags +shortest -max_interleave_delta 100M "result2.mp4"

  I tried using this command, and my output video was still 1.14 seconds long.
  I tried the command again with a different audio file (flac) and the video output had again 2 seconds of blank audio at the end. Is one of my flags causing extra space to be appended ? Can I cut the video’s length to be that of the audio file ?

• A light-weight Rust crate for encoding videos from images and audios [closed]

  24 décembre 2019, par Agus Putra Dana

  I want to make a web app that enable users to generate video from canvas animation. I’m aware that I can record the canvas animation and the audios using catureStream(), but I want to generate the video without playing the audio. Also, the video frame rate generated using this method is not consistent.

  My idea is to capture the canvas frame by frame and store them as blob to get a consistent frame rate. And then encode the video from these blobs and some audio files uploaded by the user using web assembly. I’m also aware that I can use FFMPEG to encode the video. But the file size of the compiled FFMPEG is quite big.

  Is there any light-weight video encoder library, preferably written in Rust, just for encoding video from images and audios ?