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• Adding a text overlay with constant size to a video with varying resolutions using ffmpeg

  22 décembre 2020, par BetaLixT

  I have a video with different resolutions at different points of the video and need to add a text overlay to it. I'm new with ffmpeg, the following is one of the commands I've tried

  


  ffmpeg -i input.mp4 -vf "drawtext=text='Hello World'" -c:a copy output.mp4


  


  But the output has blurry text with it resizing every few seconds (I'm guessing because of the various resolutions in the video) and some parts of the video have their aspect ratios altered.

  


  Information on input file

  


  The input.mp4 video is generated from some .h264 raw data converted to mp4 and some blank mp4 generated that are all concatenated together, following are the commands

  


  h264 to mp4 :

  


  ffmpeg a.h264 -c copy a.mp4


  


  blank mp4

  


  ffmpeg -t 5 -f lavfi -i color=c=black:s=200x200 -c:v libx264 -tune stillimage -pix_fmt yuv420p -video_track_timescale 1200000 b.mp4


  


  Concat :

  


  ffmpeg -safe 0 -f concat -i list.txt -s 720x960 -c copy input.mp4


  


  I'd be thankful for any advice on how I could achieve this

  


• How do I reverse a video in ffmpeg ?

  19 avril 2023, par Will Beeson

  - Full Error :

  


  Stream specifier 's1:v' in filtergraph description [0]split=2:outputs=2[s0][s1] ;[s1:v]reverse[s2] ;[s0][s2]concat=a=0:n=2:v=1[s3] matches no streams.

  


  - Formatted Error

  


  

  • [0]split=2:outputs=2[s0][s1] ;

  


  • [s1:v]reverse[s2] ;

  


  • [s0][s2]concat=a=0:n=2:v=1[s3]

  


  


  - Code :

  


  instances = (
    ffmpeg
    .input(self.video_file)
    .filter_multi_output(filter_name="split", outputs=2)
)
ordered_edits = []
for i in range(2):
    if i%2 == 0:
        ordered_edits.append(
            instances[i]
        )
    else:
        ordered_edits.append(
            instances[i].video.filter(filter_name="reverse")
        )
(
    ffmpeg
    .concat(*ordered_edits, a=0, v=1)
    .output('done/output.mp4')
    .run(overwrite_output=True))


  


  Looking at the error code, it seems like s1:v should be a valid reference. The only thing I can think of is that there is an issue saving an exclusive video input into a nonspecified output. The files don't actually have any audio, I just want the video.

  


  I'm lost, please help ffmpeg experts of the world !

  


• FFMPEG - How to setup volume when merging two audio streams

  6 octobre 2014, par N3sh

  I just recently entered the magic and scary world of FFMPEG and, although I found quite a lot of guides online, I need help for my current problem.

  I am merging only audio files and I would like to be able to select their volume.

  Here is my current code for merging 2 files :

  ffmpeg -i test\audio00.mp3 -i test\audio01.mp3 -filter_complex amerge 
  
  -c:a libmp3lame -q:a 0 test\output_overlay.mp3

  I tried the following code, extracted from another answer here on SO (the User was also handling video), but it doesn’t work for me :

  ffmpeg -i test\audio00.mp3 -i test\audio01.mp3 -filter_complex "[0:a]volume=0.9[a1];  
  
  [1:a]volume=0.781250[a2]; [a1][a2]amerge,pan=stereo:c0code>

  I got this error :

  [AVFilterGraph @ 030fa8c0] The following filters could not choose their formats: 
  
  Parsed_amerge_2 Consider inserting the (a)format filter near their input or output.

  Is there a simple way to change the volume for the two streams (even for just the second one, it’s the background music) with FFMPEG ?

  P.S. Also, is it possible to have some sort of ’preview’ before actually rendering the file ?