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• How to combine ffmpeg and imagemagick codes which work separately but don't work together ?

  3 octobre 2018, par senops

  These codes are getting picture dimensions and combining them one on top of the other.
  The first working code :

  @echo off&setlocal enabledelayedexpansion
  
  
  
  for /f "tokens=1,2 delims=:" %%x in ('identify -format %%w:%%h image_1.jpg') do set w1=%%x&set h1=%%y
  
  for /f "tokens=1,2 delims=:" %%x in ('identify -format %%w:%%h image_2.jpg') do set w2=%%x&set h2=%%y
  
  echo %w1% %h1% %w2% %h2%
  
  pause

  The second working code :

  @echo off&setlocal enabledelayedexpansion
  
  
  
  set /a w1=1000
  
  set /a w2=500
  
  set /a h1=700
  
  set /a h2=400
  
  
  
  if !w1! LSS !h1! (
  
    set "p1=oh/mdar:h='max(ih,main_h)'"
  
    If !w2! LSS !h2! (
  
      set "p2=oh/mdar:h='max(ih,main_h)'[1max][0max];[0max][1max]vstack"
  
    ) else (
  
      set "p2='max(iw,main_w)':h=ow/mdar[1max][0max];"
  
    )
  
  ) else (
  
    set "p1='max(iw,main_w)':h=ow/mdar"
  
    if !w2! LSS !h2! (
  
      set "p2=oh/mdar:h='max(ih,main_h)'[1max][0max];[0max][1max]vstack"
  
    ) else (
  
      set "p2='max(iw,main_w)':h=ow/mdar[1max][0max];[0max][1max]vstack"
  
    )  
  
  )
  
  
  
  ffmpeg -i image_1.jpg -i image_2.jpg -filter_complex "[0][1]scale2ref=w=!p1![0max][1ref];[1ref][0max]scale2ref=w=!p2!" -q:v 1 -y combined.jpg

  But when I put them together they don’t work :

  @echo off&setlocal enabledelayedexpansion
  
  
  
  for /f "tokens=1,2 delims=:" %%x in ('identify -format %%w:%%h image_1.jpg') do set w1=%%x&set h1=%%y
  
  for /f "tokens=1,2 delims=:" %%x in ('identify -format %%w:%%h image_2.jpg') do set w2=%%x&set h2=%%y
  
  
  
  if !w1! LSS !h1! (
  
    set "p1=oh/mdar:h='max(ih,main_h)'"
  
    If !w2! LSS !h2! (
  
      set "p2=oh/mdar:h='max(ih,main_h)'[1max][0max];[0max][1max]vstack"
  
    ) else (
  
      set "p2='max(iw,main_w)':h=ow/mdar[1max][0max];"
  
    )
  
  ) else (
  
    set "p1='max(iw,main_w)':h=ow/mdar"
  
    if !w2! LSS !h2! (
  
      set "p2=oh/mdar:h='max(ih,main_h)'[1max][0max];[0max][1max]vstack"
  
    ) else (
  
      set "p2='max(iw,main_w)':h=ow/mdar[1max][0max];[0max][1max]vstack"
  
    )  
  
  )
  
  
  
  ffmpeg -i image_1.jpg -i image_2.jpg -filter_complex "[0][1]scale2ref=w=!p1![0max][1ref];[1ref][0max]scale2ref=w=!p2!" -q:v 1 -y combined.jpg

• lavc/mjpeg : Add profiles for MJPEG using SOF marker codes

  23 novembre 2017, par Mark Thompson

  lavc/mjpeg : Add profiles for MJPEG using SOF marker codes
  This is needed by later hwaccel code to tell which encoding process was
  
  used for a particular frame, because hardware decoders may only support a
  
  subset of possible methods.
  

  • [DH] libavcodec/avcodec.h
  • [DH] libavcodec/mjpegdec.c
  • [DH] libavcodec/version.h
  • [DH] tests/ref/fate/api-mjpeg-codec-param

• How to force A/V sync using mkvmerge and external time-codes ?

  19 avril 2017, par b..

  Background

  I’m working on a project where video and audio are algorithmic interpretations of an MKV source file where I use ffmpeg -ss and -t to extract a particular region of audio and video to separate files. I use scene changes in the video in the audio process (i.e. the audio changes on video scene change), so sync is crucial.

  Audio is 48khz, using 512 sample blocks.
  Video is 23.976fps (I also tried 24).

  I store the frame onset of sceneChanges in a file in terms of cumulative blocks :

  blocksPerFrame = (48000 / 512) / 23.976
  
  sceneOnsetBlock = sceneOnsetFrame*blocksPerFrame

  I use these blocks in my audio code to treat the samples associated with each scene as a group.

  When I combine the audio and video back together (currently using ffmpeg to generate mp4(v) mp3(a) in an MKV container), the audio and video start off in sync but increasingly drifts until it ends up being 35 seconds off. The worst part is that the audio lag is nonlinear ! By non-linear, I mean that if I plot the lag against the location of that lag in time, I don’t get a line, but what you see in the image below). I can’t just shift or scale the audio to fit the video because of this nonlinearity. I cannot figure out the cause of this nonlinearly increasing audio delay ; I’ve double and triple checked my math.

  

  Since I know the exact timing of scene changes, I should be able to generate "external timecodes" (from the blocks above) for mkvmerge to perfectly sync the output !

  Subquestions :

  1. Is this the best approach (beyond trying to figure out what went wrong in the first place) ? As I’m using my video frames as a
     reference, if I use the scene changes as timecodes for the audio,
     will it force the video to match the audio or vice versa ? I’m much less concerned with the duration than the sync. The video was much more laborious to produce, so I’d rather loose some sound than some frames.

  2. I’m not clear on what numbers to use in the timecodes file.
     According to mkvmerge documentation "For video this is exactly
     one frame, for audio this is one packet of the specific audio type."
     Since I’m using MP3, what is the packet size ? Ideally, I could specify a packetsize (in the audio-encoder ?) that matches my block size (512) to keep things consistent and simple. Can I do this with ffmpeg ?

  Thank you !