Playing Video using Image Sequences (v6)

WATCHOUT version 6 brings the ability to play video in the form of  image sequences. An image sequence is a set of image files (e.g. TIFF files)  played as if they were a single video.

Hardware Requirements

In order to play image sequences, a very fast disk subsystem is required. Four fast SSD:s in a RAID 0 configuration can reach a bandwidth of about 2 gigabytes per second,  corresponding to five uncompressed 1080p image sequences at 60 frames per second. 

NOTE: The actual number of image sequences you will be able to play is likely less than this theoretical maximum due to other limiting factors.

Naming of Files

WATCHOUT imposes some restrictions on the naming of the image sequence files. 

  • The file type must be TIFF (with file extension .tif or .tiff), PNG (.png) and JPEG (.jpg, .jpeg, .jpe, .jif, .jfif or .jfi). 
  • All files must have the same extension. 
  • Files must be numbered consecutively.
  • The number of digits in the name must be the same for all files.
  • The sequence can start at any number, but would typically start at 1. 
  • The files names must all begin with the same initial string of characters.
  • The sequence number must come immediately before the perdiod and the file extension. 

In short, the file names making up the image sequence must be structured like this: 

<initial string><digits>.<extension>


Here are some valid, albeit short, image sequences:

Img0001.tiff, Img0002.tiff, Img0003.tiff

Spring2015_00001.tif, Spring2015_00002.tif, Spring2015_00003.tif


The following sequences are not valid:

Img1.tiff, Img2.tiff, …, Img432,tiff (varying number of digits)

SummerTake1_001.tif, SummerTake1_002.tiff (different extensions)

 

Folder Structure

Put all files belonging to a sequence in a folder. Avoid putting anything else in that folder, such as thumbnail files and similar. WATCHOUT is smart about selecting the files that make up the image sequence, but it’s still a good idea to keep the number of unrelated files as low as possible.

You can also use image sequences for stereoscopic video and video presplit for designated displays. In those cases, there are strict naming requirements.

For stereoscopic image sequences, create a folder with the desired media name. Inside this folder, create two subfolders named Left and Right. Those subfolders must contain the image sequence files for the corresponding eye. 

NOTE: The identical file naming convention outlined above applies to all files in both folders. Thus, if the files in the ”Left” folder are named Left0001.tiff, Left0002.tiff and the files in the right folder are named Right0001.tiff, Right0002.tiff, the image sequence will not play since the initial string of characters are different. Use the same naming convention for all files in both the Left and Right folders.

For image sequences presplit for designated displays, create a folder with the desired media name. Inside this folder, create a folder for each display on which the video will appear, using the display’s name as the folder name. As with stereoscopic image sequences, all files in all folders must use the  same naming convention.

If you want to combine both stereoscopic and presplit image sequences, create a folder with the desired media name. Inside this folder create two folders for each display, named Display1-Left and Display1-Right (replacing ”Display1” with the actual name of  your displays). Remember that all files in all folders must use the same naming convention.

Using an Image Sequence

To use an image sequence, choose ”Add Video Proxy” on the Media menu. Select ”Play from a Sequence of Still Image Files”. Optionally select the presplit and stereoscopic checkboxes as appropriate. Click “Browse” and select the base image sequence folder. WATCHOUT will count the files in the sequence and calculate the duration based on the specified frame rate. Enter the dimensions of the video (for presplit video, this is the total size across all involved displays).

Recommended File Format

While WATCHOUT will attempt to decode and play a variety of image formats (including PNG and JPEG), TIFF files are highly recommended for performance reasons. TIFF files have the following requirements for best compatibility and performance:

  • Baseline TIFF format.
  • Uncompressed (best for natural or camera sourced footage).
  • PackBits (works well for synthetic video with smooth area).
  • Single-frame. 
  • RGB color space.

Troubleshooting

Here are some tips and things to look out for when using image sequences

Playback is Jerky

Make sure the media is on a fast hard drive, preferably SSD:s in a RAID-0 configuration. Make sure all the images have the same dimensions, and that this dimension matches the one entered in the video proxy dialog. If playing tiff files, check that the compression scheme used is none or PackBits. Avoid using Huffman RLE. You may have reached the limit of what your system is capable of. As a general rule of thumb, one uncompressed 1080p video stream at 60 frames per second corresponds to 360 megabytes per second.

Plays Too Slow or Too Fast

Make sure the correct frame rate is specified in the Video Proxy dialog box.

Video Duration is Incorrect or Stops Prematurely

There are probably files missing in the sequence. For example, if the movie consists of 1000 frames, numbered 1-1000, and the file for frame 201 is missing, the image sequence will be considered to consist of only 200 frames. Also, make sure the correct frame rate is specified in the Video Proxy dialog box.

Video Doesn’t Play

Verify that the images are in a supported format (see above under “Recommended File Format”).

Stereoscopic and/or Presplit Problems

Make sure all files in all folders use the exact same naming and numbering convention (see “Naming of Files” above).