Sur d’autres sites (9244)

• avcodec/nvenc : hardcode color characteristics for internal RGB2YUV conversion

  6 août 2022, par Timo Rothenpieler

  avcodec/nvenc : hardcode color characteristics for internal RGB2YUV conversion
  nvenc does not appear to use these values as inputs for its built in RGB
  
  to YUV conversion, but instead sets them on the output as-is.
  Testing indicates the input is expected to be sRGB, with the output
  
  ending up as limited range bt.470.
  

  • [DH] libavcodec/nvenc.c

• How to make customizable subtitles with FFmpeg ?

  6 août 2022, par Alex Rypun

  I need to generate videos with text (aka subtitles) and styles provided by users.
The styles are a few fonts, text border, text background, text shadow, colors, position on the video, etc.

  


  As I understand there are 2 filters I can use : drawtext and subtitles.

  


  subtitles is easier to use but it's not fully customizable. For example, I can't add shadow and background for the same text.

  


  drawtext is more customizable but quite problematic.

  


  I've implemented almost everything I need with drawtext but have one problem : multiline text with a background.

  


  boxborderw parameter adds specified pixels count from all 4 sides from the extreme text point. I need to make backgrounds touch each other (pixel perfect). That means I have to position text lines with the same space between extreme text points (not between baselines). With crazy workarounds I solved it.
Everything almost works but sometimes some strange border appears between lines :

  


  

  


  Spending ages investigating I figured out that it depends on the actual line height and the position on the video.
Each letter has its own distances between baseline and the highest point and between baseline and the lowest point.
The whole line height is the difference between the highest point of the highest symbol and the lowest point of the lowest symbol :

  


  

  


  Now the most interesting.

  


  For lines that have even pixels height.

  


  If the line is positioned on the odd pixel (y-axis) and has an odd boxborderw (or positioned on the even pixel (y-axis) and has an even boxborderw ), then it's rendered as expected (without any additional borders).
In other cases, the thin dark line is noticeable on the contact line (it's rendered either on top or at bottom of each text block :

  


  

  

  


  For lines that have odd pixels height.

  


  In all cases the thin dark line is noticeable. Depending on y coordinate (odd or even) and boxborderw value (odd or even) that magic line appears on top or bottom :

  


  

  


  I can make text lines overlap a bit. This solves the problem but adds another problem.
I use fade-in/out by smoothly changing alfa (transparency). When the text becomes semi-transparent the overlapped area has a different color :

  


  

  


  Here is the command I use :

  


  ffmpeg "-y" "-f" "lavfi" "-i" "color=#ffffff" "-filter_complex" \
"[0:v]loop=-1:1:0,trim=duration=2.00,format=yuv420p,scale=960:540,setdar=16/9[video];\
[video]drawtext=text='qqq':\
fontfile=ComicSansMS.ttf:\
fontcolor=#ffffff:\
fontsize=58:\
bordercolor=#000000:\
borderw=2:\
box=1:\
boxcolor=#ff0000:\
boxborderw=15:\
x=(w-text_w)/2:\
y=105:\
alpha='if(lt(t,0),0,if(lt(t,0.5),(t-0)/0.5,if(lt(t,1.49),1,if(lt(t,1.99),(0.5-(t-1.49))/0.5,0))))',\
drawtext=text='qqq':\
fontfile=ComicSansMS.ttf:\
fontcolor=#ffffff:\
fontsize=58:\
bordercolor=#000000:\
borderw=2:\
box=1:\
boxcolor=#ff0000:\
boxborderw=15:\
x=(w-text_w)/2:\
y=182:\
alpha='if(lt(t,0),0,if(lt(t,0.5),(t-0)/0.5,if(lt(t,1.49),1,if(lt(t,1.99),(0.5-(t-1.49))/0.5,0))))'[video]" \
"-vsync" "2" "-map" "[video]" "-r" "25" "output_multiline.mp4"


  


  I tried to draw rectangles with drawbox following the same logic (changing the position and height). But there were no problems.

  


  Does anybody know what is the nature of that dark line ?
And how it can depend on the even/odd of the height and position ?
What should I investigate to figure out such a behavior ?

  


  UPD :

  


  Just accidentally figured out that changing the pixel format (from format=yuv420p to format=uyvy422 or many others) solved the problem. At least on my test commands.
Now will learn about what is pixel format)

  


• How to Install FFMpeg on centos 6 in 2022 ?

  17 août 2022, par Ruben Fernandes

  a client of mine asked to add videos to their website, i decided to install FFMpeg on their server so whenever they upload a video, the service automatically generates the first frame for the preview and encodes them in webm.

  


  Sadly it seems to be impossible to install without having to compile it myself (which i don't really want to do as i have never done it before and don't want to risk breaking something in their server),

  


  The server is running cento6 but EVERY repository that provides the centos6 version of FFMpeg seem to use dependencies from dead hosts (they are offline and unreachable), every solution i find ends up with the same error like "Couldn't resolve host 'apt.sw.be'"

  


  I've changed yam repositories, installed apt-get to try with that instead of yam, disabled and enable repos like nux that seem to be very outdated, even followed posts that were published/updated recently like this but they all keep ending up with the the same "Couldn't resolve host..." when installing decencies.

  


  Is there any live and updated repo that provides a way to install FFMpeg for centos6 with yum or apt-get in 2022 ?

  


  Thanks

  


  EDIT
Following Romeo's tip about downloading the binaries, i managed to install it but in my case i needed a older 32 bit version to make it work (else i'd get Kernel too old) :

  


  $ wget https://www.johnvansickle.com/ffmpeg/old-releases/ffmpeg-4.0.3-32bit-static.tar.xz
$ tar xvf ffmpeg-4.0.3-32bit-static.tar.xz
$ sudo mv ffmpeg-4.0.3-32bit-static/ffmpeg ffmpeg-4.0.3-32bit-static/ffprobe /usr/local/bin/