Sequence Viewer - Introduction


Sequence Viewer is a tool for animators, showing avi and sv video files frame by frame, or at any speed from 1/10th to 10x speed.

Video players seem to be moving away from allowing animators to step through videos, as the more advanced the algorithms become for compressing moving images, the more difficult it becomes to extract a single frame.

Sequence Viewer has two windows. The first appears like a typical video player, the second is a frame by frame analysis of colour levels through the video.

Video player

A test file is being played at a nominal 25 frames per second. Real-time playback is achieved by dropping frames. In this case, 23 frames are drawn, so two frames have been dropped to maintain the correct run speed.

The properties grid on the left shows various properties for the file.

  • It contains no audio
  • It's size on the disk is 68Mb (if you choose to count Mb that way)
  • It contains no audio
  • The frame size is 320 pixels wide by 240 pixels high
  • There are 304 frames
  • The frame rate is 25 frames per second
  • The video data is 24 bits per pixel in rgb format

This is for an .sv file, which is used only by my video products. Here are the properties for an .avi file, showing the codec used. If the codec is not present on your machine, no other information will appear until it is installed.


This .avi file uses the codec (in the format property) identified as DX50. This is known as it fourcc, or four character code. All codecs have a distinct fourcc, and they are all listed here ( A little browsing, and we discover the popular DivX Mpeg4 codec, version 5 has been used to create this video.

The file, of a mere 2.5Mb, has had its audio extracted to a .wav file ready for playing, and the size of the decompressed audio stream is a little over 4.5Mb.

Player buttons

The buttons are, in order:

Open fileOpens an .avi or .sv video file
Go to start (Home key)Moves to the beginning of a video
Step back (Left arrow)Steps one frame towards the beginning
Play in reverse (R key)Starts playing the video backwards
Play (P key)Starts playing the video
Stop (S key)Stops play
Step forward (Right arrow)Steps one frame towards the end
Go to end (End key)Moves to the last frame
Loop (L key)Allows the video to loop from the end back to the beginning, if playing forwards, or from the end back to the beginning if playing in reverse. If markers are set, the video will loop between the nearest two markers
Play speedThe playing speed of the video can be selected. Audio also plays at the requested speed, so it is pitched up if playing faster, and down if playing slower than normal.
Add marker (M key)Adds a marker at the current frame
Clear markers (Ctrl-M)Removes all markers
Audio (A key)Turns audio on or off
AnalyzeAnalyzes colour and light levels across each frame (the subject of the next section)
Up arrowIncrease the playing speed by 10%
Down arrowDecrease the playing speed by 10%
MousewheelScroll through the frames one step at a time in either direction
TrackerDrag the tracker to any frame
Right click the tracker to set and clear markers
Menu | Edit | Go to frameEnter the frame to go to

The audio file can be saved from the menu, or the current frame exported to a file or to the clipboard.
Video analysis

The rgb only graph shows the range of red, blue and green colour values, from max to min. The maximum colour is the highest value of any colour component of any pixel in each frame, and min is the lowest value of any colour pixel in a frame. Each frame is calculated separately, and presented along the X axis. In the above diagram, the initial fade in, then fade out and fade in again approx 1/3 through the sequence can be seen clearly. The average values are shown as a white line.

HSV or HSL colour spaces can also be displayed. Here is the HSV analysis of the same sequence.

However, without any information on the actual density of colour, or colour value across each frame, maxima and minima are of limited value.

The density button (the rightmost button with 3 blended stripes) changes the display between maxima and minima to a density plot. The next figure shows the density equivalent of the above two figures.

This analysis clearly shows the scene changes, and that the colours are limited in bands, indicating that this is a cartoon with an unmoving background for each scene. The space to the left shows that the early frames are largely dominated by a black background during the title run.

Dragging the mouse with the left mouse button clicked, or clicking on the analysis window displays the relevant frame in the viewer window.

For a comparison, here is the analysis of a short video without scene changes taken in my back garden.

This analysis shows that the dominant hues range from red to blue, with far more variation than the cartoon. Perhaps I could have titilated viewers more my moving to a purple hued image for part of the sequence.


A Sequence Viewer licence, which allows installation on one computer, is GBP9.95. For bulk licensing, please email me.

How to buy

Click the button to buy with Paypal.

For corporate purchasing, send a purchase order by email to the address at the top of this page. If you wish to send a purchase order by post, please email me for my postal address.

Once your order is received, the installer will be emailed to you in a zip file.

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