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• How to concatenate two AAC files smoothly ?

  15 août 2013, par James Deng

  To save time, I want to segment and transcode a large video file on multiple computers.

  I use ffmpeg to transcode the segments of the large video file with :

  ffmpeg -i large_movie.mp4 -ss 00:00:00 -t 00:01:00 -acodec libfaac seg0.flv
  
  ffmpeg -i large_movie.mp4 -ss 00:01:00 -t 00:01:00 -acodec libfaac seg1.flv
  
  ...

  And concatenate the segments with :

   ffmpeg -i concat.conf -vcodec copy -acodec copy result.flv

  The content of the concat.conf :

  ffsconcat version 1.0
  
  file seg0.flv
  
  file seg1.flv
  
  ...

  Now we get a result FLV file result.flv content all the segments. But when I play this file, I found the segment boundary audio may be momentarily interrupted ! I'm sure those segments is closely associated, and the timestamp is right.

  When I decode the AAC sample in segment file to a wave format, and open the wave with CoolEdit, I found at the front and the end of the file, the value of audio sample is very small (mute ?) ! At the front of the file, there is about 21ms 'mute' sample. And at the end of the file, there is about 3ms 'mute' sample.

  Is the mute samples result the momentarily interrupt ? How to concatenate media file containing AAC smoothly ?

  ---

  After further testing, I found if you split a wave file to small wave files, then encode this small wave files to small aac file use faac :

  faac -P -R 48000 -B 16 -C 2 -X -o 1.aac 1.wav
  
  faac -P -R 48000 -B 16 -C 2 -X -o 2.aac 2.wav
  
  faac -P -R 48000 -B 16 -C 2 -X -o 3.aac 3.wav
  
  faac -P -R 48000 -B 16 -C 2 -X -o 4.aac 4.wav
  
  faac -P -R 48000 -B 16 -C 2 -X -o 5.aac 5.wav

  The console output like this :

  [hugeice@fedora19 trans]$ faac -P -R 48000 -B 16 -C 2 -X -o 5.aac 5.wav
  
  Freeware Advanced Audio Coder
  
  FAAC 1.28
  
  
  
  Quantization quality: 100
  
  Bandwidth: 16000 Hz
  
  Object type: Low Complexity(MPEG-2) + M/S
  
  Container format: Transport Stream (ADTS)
  
  Encoding 5.wav to 5.aac
  
     frame          | bitrate | elapsed/estim | play/CPU | ETA

  And concatenate this small aac files to a big aac files use :

  cat 1.aac 2.aac 3.aac 4.aac 5.aac > big.aac

  Now, if you play the big.aac, there is a momeniary interrupt at the segment boundary !

  The question becomes how segment coding and concatenate aac files smoothly ?

• ffmpeg does not sync audio and video recording

  30 avril 2020, par Ferrum3000

  I'm using followig command record mic+speakers+video screen, but in result file screen.avi, video showes +0,5 second early, than sounds.
Please help to fix it.

  



  ffmpeg ^
 -f dshow -i audio="Стерео микшер (Realtek High Definition Audio)" ^
 -f dshow -i audio="Mic in at front panel (Pink) (Realtek High Definition Audio)" ^
 -f gdigrab -framerate 60 -video_size 1920x1080 ^
 -draw_mouse 1 ^
 -i desktop -vcodec libx264 -pix_fmt yuv420p -preset ultrafast ^
 -filter_complex "[0:a][1:a]amerge=inputs=2[a]" -map 2 -map "[a]" ^
 screen.avi

  


• How to stream video in the GUI using PyQt5 ?

  30 mars 2020, par Shriya

  I am a newbie with Python as well as ffmpeg. Once the webcam is assigned to the Pine, the video gets stored in the /mnt/hls directory. The video from this directory needs to be displayed on the Front End which was designed using QtDesigner and the wiring is done using PyQt5. The video needs to be displayed when a button is clicked by the user in the OpenGLWidget.
The command line for the video stream is "Ffplay -fflags nobuffer -flags low_delay [HLS playlist]", which can be run using os.system(). My issue is with getting the video displayed in the OpenGLWidget. Could someone help me through this or direct me to another similar question or a different link ? Thank you.