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• Feeding a series of images to ffmpeg as each image is created [closed]

  5 février 2013, par Mark Schneider

  I'm trying to use ffmpeg to build a 1280x720 slide-show from a sequence of pictures and videos, but I have concerns about potential disk I/O bottleneck.

  I expect a typical slide-show to have about 50 pictures and 2-3 videos (10-15 seconds each at 30 fps). I would like to show each picture for 3-4 seconds (possibly with a
  Ken Burns effect) with a smooth 2 second crossfade between each set of pictures (or for pictures adjacent to videos - between the picture and the first/last frame of the video).

  Given about 50 pictures, the crossfades alone would amount to about 3,000 images (50 transitions x 2 secs/transition x 30 fps). And I suppose if I implement a Ken Burns effect during each picture's 3-4 second showing, I'd have to provide ffmpeg with individual images for each of those frames. (I'm writing a script in Ruby that will pull a list of images from a database and in turn call ImageMagick to create the individual images for each frame. As I understand it, the RMagick library interfaces with ImageMagick such that the output images come back as in-memory objects without needing to write to disk. FWIW, I'm developing in Windows 8 and will deploy to Heroku.)

  All of the slideshow examples I've found online feed ffmpeg a set of images which have already been created. However, in an effort to avoid waiting on considerable disk I/O, I'd like to feed each image to ffmpeg as the image is created rather than create them all in advance.

  Is there a way to send each image file to ffmpeg on the fly as the file is created in memory ?

• ANSI Code Coverage Followup

  9 mars 2012, par Multimedia Mike — Programming

  The people behind sixteencolors.net noticed my code coverage project concerning the ANSI video decoder and asked what they could do to help. I had already downloaded 350 / 4000 of their artpacks but didn’t want to download the remainder if I could avoid it. They offered to run my tool against their local collection of files.

  Aside : They have all of the artpacks archived at Github.

  The full corpus of nearly 4000 artpacks contains over 146,000 files. Versus my sampling of 350 artpacks and 13,000 files that covered all but 45 lines of the ansi.c source file, the full corpus has files to exercise… 6 more of those lines. Whee. This means that there are files which exercise the reverse and concealed attributes, all 3 “erase in line” modes, and one more error path (which probably wasn’t a valid file anyway).

  Missing features mostly cluster around different video modes, including : 320×200 (25 rows), 640×200 (25 rows), 640×350 (43 rows), and 640×480 (60 rows) ; on the plus side, nothing tripped the “unsupported screen mode” case. There are no files that switch modes during playback.

  I guess statistical sampling theory holds out here– a small set of randomly chosen files would do a fine job covering code. But this experiment is about finding the statistical outliers.

• Size Discrepany in the ‘du’ Command

  22 juin 2012, par Multimedia Mike — General

  I had a problem today while using the common Unix command ’du’. As a refresher, ’du’ stands for disk usage and is a handy tool for understanding how much disk space is being occupied.

  I think ’du’ is probably doing the right thing. The problem might be that I’m getting strange (read : 1/2 the expected number) when running the tool against directories on vmhgfs, the VMware filesystem.

  Science Project
  On an Ubuntu Linux VMware session, my home directory is on the main file system, which is ext4. The directory /mnt/hgfs is reported by ’mount’ to be of type vmhgfs and is shared with the host machine.

  Create a directory in the home directory and generate a 10 MiB file :

  mkdir /home/melanson/dir
  dd if=/dev/urandom of=/home/melanson/dir/random-file bs=1048576 count=10
  

  Create a directory on the shared drive and copy the same file :

  mkdir /mnt/hgfs/vmshare/dir
  cp /home/melanson/dir/random-file /mnt/hgfs/vmshare/dir
  

  Run ’du’ on each directory using the -k and -h options :

  du -k /home/melanson/dir /mnt/hgfs/vmshare/dir
  10244   /home/melanson/dir
  5120    /mnt/hgfs/vmshare/dir
  du -h /home/melanson/dir /mnt/hgfs/vmshare/dir
  
  11M    /home/melanson/directory
  
  5.0M   /mnt/hgfs/vmshare/directory
  

  I noticed this discrepancy when I was trying to pack a set of files (akin to ’tar’-ing) living in a directory in the shared location. I was going mad trying to understand why the original directory was only 2 MB as reported by ’du’ but the final packed file was 4 MB.

  To be fair, the man page for ’du’ succinctly states that the tool’s purpose is merely to "estimate file space usage".