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• FFmpeg recording audio from several sources

  4 avril 2017, par Valery Shevchuk

  everyone.
  I’m trying to use FFmpeg to record video and 3 audio sources and use it to generate 3 different video files - each file should contain the same video stream but the different audio stream. The problem is that I got audio sync issues. The first audio stream is synced perfectly, but the second one has 1 sec lag, and the third one has like 2 sec lag.

  I’ve made a few tests so far and it seems that root cause of the issue is initialization time of video/audio devices. So, one device is already recording something but the second is still being opened and so on. I’ve tried to change input devices order and after that audio streams still have the same issue BUT if before 2nd and 3rd audio streams were some time ahead of video, after reordering they became to lag after the audio (audio for the same event appears with some delay). So this test confirms my version about device initialization times.

  But the question still, why the first audio stream is synchronized properly, while other 2 are not. and also, how could I overcome this issues ? Any workarounds and ideas are highly appreciated.

  Here is FFmpeg command I’m using and it’s output.

  ffmpeg.exe -f dshow -video_size 1920x1080 -i video="Logitech HD Webcam
  C615" -f dshow -i audio="Microphone (HD Webcam C615)" -f dshow -i
  audio="Microphone Array (Realtek High Definition Audio)"
  -filter_complex "[1:a]volume=1[a1] ;[2:a]volume=1[a2]" -vf scale=h=1080:force_original_aspect_ratio=decrease -vcodec libx264
  -pix_fmt yuv420p -crf 23 -preset ultrafast -acodec aac -vbr 5 -threads 0 -map v:0 -map [a1] -map [a2] -f tee
  "[select=\’v,a:0\’]C :/Users/vshevchu/Desktop/123/111/111_jjj1.avi|
  [select=\’v,a:1\’]C :/Users/vshevchu/Desktop/123/111/111_jjj2.avi"

  OUTPUT

  PS. Actually, the issue is exactly the same when I’m not using "tee" muxer but writing all the audio streams to one container. So, "tee" isn’t a suspect.

• FFMPEG corruption concat

  11 avril 2017, par Please Help

  When I run

  ffmpeg -f concat -i resizedvideolist.txt -c copy concatenated_time.mp4 2>&1

  it concatenates all the videos in the txt, but there is one video around halfway through that get glitched out. The audio just doesn’t play for that video, but then starts playing on the next video, so it has been delayed. Then somewhere the audio managed to catch up and gets back in sync. Seems like some major corruption going on here.

  I do not know how to fix this as the codec is the same as all the other vidoes, H.264, it is an mp4 like the others. The individual video file runs fine as it is, and it already is in the same timescale, because before this ffmpeg command, I ran

  ffmpeg -i ./tempDownloadedMemes/$videoFileName -filter_complex 'scale=1080:-1,pad=1080:1080:(ow-iw)/2:(oh-ih)/2:0x2F2F2F' -video_track_timescale 15360 ./resizedVideos/resized_videoFileName 2>&1

  To be honest I don’t even know what timescale is, but I read that it needs to be the same for it to work. I deleted the video from the list, tried this same command, and the problem was gone at the same time in the video that it would have appeared. It seems like it is something to do with that one file itself. Any known issues/workarounds on concat bugs ? This is very important to me. Thanks.

• Extend + scale a portrait video so the aspect ratio stays and the black borders become a blurry version of the video

  24 avril 2017, par P. Dee

  I have a 720 x 1280 pixels video. How do I extend and scale it to 1920 x 1080 such that the aspect ratio is being kept and the black borders are a blurry version of the video, so you don’t really notice that it’s just a small vertical stripe.

  Example

  

  

  I started with

  ffmpeg -i video720x1280.mp4 -vf "scale=608:1080,pad=width=1920:height=1080:x=656:y=0:color=black" video1920x1080.mp4