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• FFMPEG cropping size is always wrong

  19 avril 2020, par Samsy

  I need a bunch of video to be EXACTLY 1024x512 ( power of 2 video ), not a pixel less, not a pixel more..

  



  I'm scaling them first to 1024 width

  



  Then cropping them to 1024x512

  



  Problem is..

  



  result always ends up with 1 pixel more or 2 less pixels in width etc...

  



  Source dimension : 1624 × 1080
Output dimension : 1022 × 512


  



  Source dimension : 1264 × 720
Output dimension : 1025 × 512


  



  rm -R ./output

mkdir output

cd input

for i in *.mp4;

  do name=`echo "$i" | cut -d'.' -f1`

  FILE="${name}"

  TMP="temp.mp4"

  INPUT="${FILE}.mp4"

  OUT_PUT="../output/${FILE}.mp4"

  JPEG_OUTPUT="../output/${FILE}.jpg"

  echo FILE

  echo INPUT

  ffmpeg -i $INPUT -filter:v scale=1024:-2 -c:a copy ${TMP}

  ffmpeg -i ${TMP} -filter:v "crop=1024:512:exact=1" -c:a copy ${OUT_PUT}

  # ffmpeg -loglevel panic -i $OUT_PUT -vframes 1 -f image2 $JPEG_OUTPUT

  rm ${TMP}

done


  


• Video playing, how to play a video back a a rapid rate at random timestamp locations

  10 avril 2020, par Zarc Rowden

  Note : this is a mildly general question that is looking more for pointers in the right direction and not exactly requiring a concise coded answer. I appreciate any and all input, thank you for lending your brain power to me for this moment :)

  



  I have a script that receives midi messages in real time and triggers playback of a single video on various timestamps that are changed/selected regularly and randomly by a user. Currently this is working in the browser, however, I've realized that there is some noticeable latency between (i'm guessing the cause here so please correct me) the moment a request to play a video at a specific time is made(note : the video is not being requested over the wire, this action does not take place until a JS Blob Url is loaded into the player) and the moment where that request is fulfilled and delivered from storage to pixels on the screen.

  



  My question is : Is it reasonable to assume that there is a tool out there, that given the correct video format and optimizations both in the code and in the file that could load an entire, say : 1 gb video into memory and play it back at random timestamps every 60 milliseconds at completely random, constantly changing timestamps.

  



  If you're now all the way down here... Thanks for reading this far, or scanning ! Please let me know if this question makes any sense / could be improved, I'm happy to clarify further.

  


• FFMPEG Stream via UDpxy and HDMI Grabber

  4 mars 2020, par Fabian Schäfer

  We use a HDMI Grabber and the manual from here : https://blog.danman.eu/reverse-engineering-lenkeng-hdmi-over-ip-extender/
  You can find the Script here : https://gist.github.com/danielkucera/0a2f36bc53959e4879cb567149aafb78

  Now we want to grab the Stream via FFMPEG and UDPxy to TVHeadEnd. But FFMPEG produces some Error as you can see below.

  FFMPEG Configuration :

  sudo ./recvlkv373.py 226.2.2.2 2068 /dev/stdout | ffmpeg -re -i pipe: -c:v h264 -c:a copy -f mpegts udp://239.0.0.1:1234

  [mjpeg @ 0x5578d5a232e0] error count: 73e1c90ea5aa3699
  
  [mjpeg @ 0x5578d5a232e0] error y=80 x=15
  
  frame=  746 fps= 25 q=28.0 size=     229kB time=00:00:27.48 bitrate=  68.2kbits/s speed=0.922frame=  758 fps= 25 q=28.0 size=     231kB time=00:00:27.96 bitrate=  67.7kbits/s speed=0.923frame=  771 fps= 25 q=28.0 size=     234kB time=00:00:28.48 bitrate=  67.2kbits/s speed=0.924frame=  783 fps= 25 q=28.0 size=     236kB time=00:00:28.96 bitrate=  66.7kbits/s speed=0.925frame=  796 fps= 25 q=25.0 size=     242kB time=00:00:29.48 bitrate=  67.2kbits/s speed=0.926frame=  809 fps= 25 q=28.0 size=     291kB time=00:00:30.00 bitrate=  79.5kbits/s speed=0.928frame=  821 fps= 25 q=28.0 size=     294kB time=00:00:30.48 bitrate=  79.1kbits/s speed=0.928frame=  834 fps= 25 q=28.0 size=     298kB time=00:00:31.00 bitrate=  78.8kbits/s speed=0.93xframe=  847 fps= 25 q=28.0 size=     301kB time=00:00:31.52 bitrate=  78.1kbits/s speed=0.931[mjpeg @ 0x5578d5a232e0] error count: 65b697ff00611d13
  
  [mjpeg @ 0x5578d5a232e0] error y=0 x=45
  
  frame=  859 fps= 25 q=28.0 size=     303kB time=00:00:32.00 bitrate=  77.5kbits/s speed=0.932frame=  872 fps= 25 q=28.0 size=     309kB time=00:00:32.52 bitrate=  77.8kbits/s speed=0.933[mjpeg @ 0x5578d5a232e0] error count: 6464e73ce47d9ba1e
  
  [mjpeg @ 0x5578d5a232e0] error y=73 x=10
  
  [mjpeg @ 0x5578d5a232e0] mjpeg_decode_dc: bad vlc: 0:0 (0x5578d5a2a328)
  
  [mjpeg @ 0x5578d5a232e0] error dc
  
  [mjpeg @ 0x5578d5a232e0] error y=74 x=38
  
  [mjpeg @ 0x5578d5a232e0] error count: 64cd4eab52d7b5de8

  When I do it Step by Step (Save the File via the Script and then transcode with FFMPEG) everything works fine.
  When I use a Pipe the Video Quality is bad with flicker.
  It only runs rudimentary good when I use a buffer, a crf higher than 35 and Youtube with Speed 0.25.

  First, it runs on a Raspberry Pi 3, now it is on a dedicated server. Is it possible that the Server still has not enough Power for it or is FFmpeg just limited ?
  OS : Ubuntu
  CPU : i7-3770k
  RAM : 8GB DDR3
  Graphic : Quadro M4000
  

  Have you some suggestions about what to change, that the stream would run better ?