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• lavu/riscv : use Zbb REV8 at run-time

  30 mai 2024, par Rémi Denis-Courmont

  lavu/riscv : use Zbb REV8 at run-time
  This adds runtime support to use Zbb REV8 for 32- and 64-bit byte-wise
  
  swaps. The result is about five times slower than if targetting Zbb
  
  statically, but still a lot faster than the default bespoke C code or a
  
  call to GCC run-time functions.
  For 16-bit swap, this is however unsurprisingly a lot worse, and so this
  
  sticks to the baseline. In fact, even using REV8 statically does not
  
  seem to be beneficial in that case.
           Zbb static    Zbb dynamic   I baseline
  
  bswap16 :  0.668184765   3.340764069   0.668029012
  
  bswap32 :  0.668174014   3.340763319   9.353855435
  
  bswap64 :  0.668221765   3.340496313  14.698672283
  
  (seconds for 1 billion iterations on a SiFive-U74 core)
  

  • [DH] libavutil/riscv/bswap.h

• ffmpeg video replay with time-sync needs actual recording times

  16 juillet 2018, par navySV

  I am attempting to use ffmpeg to replay multiple video files time-synched, but the zero-based video start time is preventing this.

  I have ffmpeg commands to successfully capture a Microsoft Windows 7 desktop into a video file and replay it with a timestamp value (see below), but the internal timestamp is always starting near zero. How can ffmpeg display the actual time when the video was recorded (and not the time since the start of the video i.e. zero) ?

  For example, if the video started to be recorded at 10:47 am, the ffplay command should display a timestamp similar to "10:47:31" during playback (and not "00:00:31").

  video-capture command :

  ffmpeg -f gdigrab -offset_x 0 -offset_y 0 -video_size 1920x1080 -i desktop -c:v libx264 -preset medium -f mpegts -framerate 24 -y fileA.ts

  playback command :

  ffplay -vf "drawtext=fontfile=/windows/fonts/arial.ttf: text='%{pts\:gmtime\:0\:%H\\\:%M\\\:%S}':box=1:x=(w-tw)/2:y=h-(2*lh)" fileA.ts

  parameters I’ve tried unsuccessfully in the previous commands (including moving these around into different places in the commands) :

  -timestamp now
  
  
  
  -vsync 0
  
  
  
  -copyts

  (every attempt to use -copyts generates errors about "non-strictly-monotonic PTS" or "Non-monotonous DTS in output stream" no matter where I put this parameter)

  -filter_complex "[0:v] setpts=PTS"

  The ultimate goal is to capture four video files (recorded on four different computers and probably having different start times), and then to replay all four in time-sync (which is not possible using only the zero-based start times).

  For example, I’ve been successful at replaying four video files in a 2x2 arrangement, using the following command (I added the -ss parameter to demonstrate I can move the start time of the replay). Unfortunately, they always time-sync to the zero-based first video frame (so they all play from the beginning of the video file). I need the replay to be time-syncing to the actual recorded time for each video. If the four videos were captured starting at times 10:47:00, 10:47:51, 10:48:44, and 10:49:01, I want to be able to replay all of them so that all are displaying the same timestep at the same time (so if one video were displaying 10:48:33, all of the videos would be displaying the same time or a blank screen if that time was unavailable) .

  ffmpeg -ss 00:00:30 -i fileA.ts -i fileB.ts -i fileC.ts -i fileD.ts -filter_complex "[0:v][1:v]hstack[top];[2:v][3:v]hstack[bottom];[top][bottom]vstack[v]" -map "[v]" -timestamp now -f mpegts - | ./ffplay - -x 1920 -y 1080

  Ideally, I would also like to be able to use a real time value (something like "ffplay -ss 10:48:00 ...") to start the video replay at a different position, but worst-case I can write a script to do the needed conversion of the time value.

  My ffmpeg version is a Windows 7 64-bit static build "N-90810-g153e920892" on 2018Apr22 (downloaded from https://www.ffmpeg.org/download.html)

• Add text with FFMpeg drawtext at specific time

  17 avril 2017, par nbrogi

  I’m adding text to an animated GIF.

  I would like the text to appear at a specific time, though, and I’m unable to do that.

  This is what I have :

  ffmpeg -i image.gif -vf 'drawtext=textfile=/path/to/text.txt:x=0:y=0:fontfile=/path/to/font.ttf:fontsize=64:fontcolor=white:borderw=3:bordercolor=black:box=0'

  I tried different approaches, but nothing seems to work. I can manipulate timing for the video using things like -itsoffset 00:00:30, but not the text.