Brtdku

Consider the following bash script (on Ubuntu 18.04, melt 6.6.0), which uses melt to make a slideshow and play it locally in a window (SDL consumer), mostly copied from https://mltframework.org/blog/making_nice_slideshows/ ( edit: I'm aware that's its possible to specify files individually as in https://superuser.com/questions/833232/create-video-with-5-images-with-fadein-out-effect-in-ffmpeg/834035#834035 - but that approach seems to scale images during transition, and takes quite a while to "render" before playing in SDL window, while this one has nearly instant playback):

echo "

description=DV PAL

frame_rate_num=25

frame_rate_den=1

width=720

height=576

progressive=0

sample_aspect_num=59

sample_aspect_den=54

display_aspect_num=4

display_aspect_den=3

colorspace=601

" > my-melt.profile



mkdir tmppics

convert -background lightblue -fill blue -size 3840x2160  -pointsize 200  -gravity center label:"Test A" tmppics/pic_01.jpg

convert -background lightblue -fill blue -size 3840x2160  -pointsize 200  -gravity center label:"Test B" tmppics/pic_02.jpg



melt -verbose -profile ./my-melt.profile 

./tmppics/.all.jpg ttl=6 

-attach crop center=1 

-filter luma cycle=6 duration=4 

-consumer sdl

• When I run the above command, the video shows the two images loop, but the frame counter keeps on going, increasing indefinitely. How do I make it stop after the exact amount of frames that the loop is long?


• As far as I can see, the size of the output video is controlled by a profile; that is, even if I don't specify -profile, a default one is assumed; is that correct?


• The original images look like this:

... and the video looks like this:

... which means the aspect ratio is wrong; additionally I can see jagged edges, meaning the scaled image in the video is not antialiased.

How do I make the image fit in video size with correct aspect ratio, with antialiasing/smoothing? (I guess it has to do with -attach crop center=1, but I couldn't find documentation on that).

• When viewing stuff in SDL and stepping through frames, are frames numbered 0-based, - or are they 1-based, and at frame 0 simply the same frame as 1 is shown?




• If I use ttl=6 and -filter luma cycle=6 duration=4, I get this:

... that is, visible transition starts at frame 7 (frame 6 is full image A), lasts for frames 7 and 8, and ends at frame 9 (which is full image B); then again at frames 13 and 14 (frame 15 is full image A)

However, if I use ttl=6 and -filter luma cycle=6 duration=2, then I get this:

... that is, there is no transition, image instantly changes at frame 7, then again at frame 13, etc.

So, I'd call the first case a transition duration of 2 frames, and the second case a duration of 0 frames - yet the options are duration=4 and duration=2, respectively. Can anyone explain why? Where are those 2 frames of difference gone?

• 
  

  Can I - and if so, how - do the same kind of slideshow, except with fade to black? I'd like to define a "time to live" (ttl) of 6 frames per image, and a transition of 4 frames, such that:

  
  
  
  
  
  • first, 4 frames are shown of image A;
  
  
  • then one frame image A faded, followed by one frame black (amounting to 6 frames TTL for image A, the last 2 transition);
  
  
  • then two frames image B faded (amounting to 4 frames transition with previous 2), followed by two more frames image B full (so 4 frames here of image B);
  
  
  • then one frame image B faded, followed by one frame black (amounting to 6 frames TTL for image B);
  
  
  
  

... etc.

• Is it possible to persuade melt to use globbing to select images for slideshow, instead of using .all.jpg? As far as I can see on MLT (Media Lovin' Toolkit) Photo Slide Video no - but maybe there is another approach...