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• Transcode HLS Segments individually using FFMPEG

  27 mai 2013, par rayh

  I am recording a continuous, live stream to a high-bitrate HLS stream. I then want to asynchronously transcode this to different formats/bitrates. I have this working, mostly, except audio artefacts are appearing between each segment (gaps and pops).

  Here is an example ffmpeg command line :

  ffmpeg -threads 1 -nostdin -loglevel verbose \
  
     -nostdin -y -i input.ts -c:a libfdk_aac \
  
     -ac 2 -b:a 64k -y -metadata -vn output.ts

  Inspecting an example sound file shows that there is a gap at the end of the audio :

  

  And the start of the file looks suspiciously attenuated (although this may not be an issue) :

  

  My suspicion is that these artefacts are happening because transcoding are occurring without the context of the stream as a whole.

  Any ideas on how to convince FFMPEG to produce audio that will fit back into a HLS stream ?

  ** UPDATE 1 **

  Here are the start/end of the original segment. As you can see, the start still appears the same, but the end is cleanly ended at 30s. I expect some degree of padding with lossy encoding, but I there is some way that HLS manages to do gapless playback (is this related to iTunes method with custom metadata ?)

  
  

  ** UPDATED 2 **

  So, I converted both the original (128k aac in MPEG2 TS) and the transcoded (64k aac in aac/adts container) to WAV and put the two side-by-side. This is the result :

  
  

  I'm not sure if this is representative of how a client will play it back, but it seems a bit odd that decoding the transcoded one introduces a gap at the start and makes the segment longer. Given they are both lossy encoding, I would have expected padding to be equally present in both (if at all).

  ** UPDATE 3 **

  According to http://en.wikipedia.org/wiki/Gapless_playback - Only a handful of encoders support gapless - for MP3, I've switched to lame in ffmpeg, and the problem, so far, appears to have gone.

  For AAC (see http://en.wikipedia.org/wiki/FAAC), I have tried libfaac (as opposed to libfdk_aac) and it also seems to produce gapless audio. However, the quality of the latter isn't that great and I'd rather use libfdk_aac is possible.

• Evolution #2346 (Nouveau) : insérer des cache directory tag dans les dossiers temporaires

  20 septembre 2011, par b b

  Cela pourrait être utile que SPIP insère tout seul comme un grand des fichiers "cache directory tag" dans /tmp et /local pour faciliter la tâche aux gens qui utilisent tar pour faire des backups de leur sites. http://www.gnu.org/s/automake/manual/tar/exclude.html (...)

• Adjusting webcam settings before shooting a photo (v4l2 and fswebcam)

  18 septembre 2021, par Mikey

  I'm shooting photos with

  


  sudo fswebcam -d /dev/video0 -r 1920x1080 --no-banner /media/networkshare/public/"Temp Photo Holder SolidScape Right"/timelapse_$DATE.jpg


  


  on a Raspberry Pi 3 B+ running a recent version of Raspbian.

  


  The script is controlling a Logitech c920 that has adjustable features like focus, brightness, contrast, etc.

  


  I think the reason the 'manual' settings are not being saved is because I call the v4l2-ctl commands, add a delay, and then use fswebcam to shoot, like so :

  


  #!/bin/bash
DATE=$(date +"%y%m%d%H%M%S")
#sudo v4l2-ctl -d /dev/video0 -c focus_auto=false
#sudo v4l2-ctl -d /dev/video0 -c focus_absolute=35
sudo v4l2-ctl -d /dev/video0 -c brightness=128
sudo v4l2-ctl -d /dev/video0 -c contrast=128
sudo v4l2-ctl -d /dev/video0 -c saturation=128
sudo v4l2-ctl -d /dev/video0 -c gain=15
sudo v4l2-ctl -d /dev/video0 -c sharpness=128
sleep 2

sudo v4l2-ctl -c exposure_auto_priority=1

#fswebcam -d /dev/video0 -r 1920x1080 --no-banner /media/networkshare/public/RasPi/"Temp Photo Holder SS"/timelapse_$DATE.jpg

sudo fswebcam -d /dev/video0 -r 1920x1080 --no-banner /media/networkshare/public/"Temp Photo Holder SolidScape Right"/timelapse_$DATE.jpg

sleep 9

sudo fswebcam -d /dev/video0 -r 1920x1080 --no-banner /media/networkshare/public/"Temp Photo Holder SolidScape Right"/timelapse_$DATE.jpg

sleep 9


  


  How can I take a photo with manual settings appended ? Maybe I need to add commands to fswebcam inline instead of calling v4l2-ctl first ?