About Video

I have sometimes got questions about why video from the dance reports do not play. Although the subject strictly is not one of those covered in this site, I will try to give some explanations and advices.

Advices when experiencing problems with video - summary

The problem

Video is demanding. An ordinary video for VHS video players, using the European PAL format, has 25 pictures per second using approximately one half of the resolution of the TV itself, or close to 320 x 240 pixels. This is the same resolution as the best videos that the Dance Reports currently use. The source for these videos are mostly Mini DV, which is capable to store the same resolution as the TV can display, and with stereo sound as well.

A high bandwidth is required to send such pictures and video in the source quality without any compression, much more than internet and computers can deal with. One single second of uncompressed video would use about 30 MBytes. Compare this with the broadband connections to internet available today, mostly giving from 0.5 to 10 Mbit, and dialled connections perhaps giving 0,05 Mbit at ideal conditions. As these are bits while the file sizes are in bytes, you need to divide the transfer rate by approximately 10 to get the number of bytes per second.

And then add to this that these transfer capabilities are somewhat theoretical, in many situations the actual transfer rate can be much lower due to limitations somewhere along the route from the source to your own computer.

To address this problem, video is compressed before it is published. The compressed contents is transferred to your computer, and - providing that the software to decompress it is available on your computer - it is decompressed again there before it is played.

Most of us have met compressed information. Music compressed to MP3 is widely spread, and pictures compressed to JPG are not only used on internet, but almost anywhere where pictures are handled digitally, including most digital cameras.

For video as for music and pictures, there are however more than one alternative for the compression. To mention a few, pictures can be compressed to PNG, music to Ogg Vorgis and video can be compressed using many different compressors.

The video is mostly compressed both for each image with methods similar to JPG for photos, and between adjacent images so only what is changed between the images is stored and sent. If for example a static object like a house is filmed using a tripod, all frames will be more or less identical, and much resources can be saved by just sending what has been changed between each frame. But also in a such situation the lightening might be changed by clouds, and the difficult question is to decide how much of the changes should be ignored to balance between video quality and the size of the rendered file.

The compressing techniques used for internet almost always decreases the quality of the video, because of the need to make the video file size smaller. The following methods are used:

There are many programs available for compressing both video and sound. A compressing/decompressing program is often called codec.

Although sound can have similar problems as video, the sound problems are less complicated. As Dansglädje so far hardly use any sound - basically to avoid eventual conflicts with the creator's copyright to the music - I will here concentrate on video.

What is needed to play video over internet

1. A program is needed able to play video. Several such exist, some of the most well known are Media Player (Microsoft), Quick Time (Apple) and Real Player. But there are several other very capable players as well, some of them created by home users and made available as freeware. One such that I can recommend is VLC, downloadable from http://www.videolan.org. As with all other programs, these players are developed and new releases become available rather frequently. If you have permission on your own computer, it is probably a good idea to upgrade the players when new releases become available. Those using Windows Media and Windows Update (http://windowsupdate.microsoft.com), might get a message when it is time to upgrade. At least for those using Windows, this is also a good idea because of security issues.
    
2. As explained above it is not enough with a video player, you need also a corresponding codec that the video was compressed with to decompress it. This might be one of the most common sources for problems, and thus a reason to explain further. The older compression programs used, like Cinepak Radius, is playable on a wide range of computers. But the compressing is rather inefficient, giving big files or poor quality. So there are reasons to use a more modern codec, but that might lead to other problems. Microsoft have patent rights on their newer compression programs in USA - not only for the program that compress and decompress the video, but also for the protocol itself.
   
   My understanding of the implications of this is:
   
   Any contents compressed using this protocol is owned by Microsoft in the aspect that it is not allowed to be decompressed without permission/license from Microsoft. This is regardless of the legal rights of the source - that is - even if you are the legal owner of the source materials and have the copyright to it, you have still not the right to decompress it - also if it is for your own use - without permission from Microsoft. I am not sure whether this applies in Europe, but it means regardless of that that a gorge exists as my intents with publishing my materials on internet is that it should be readable for anyone.
   
   The implications of this is that those competing with Microsoft need permissions to decompress the contents, something that they do not always have. So some media players might not be permitted to play the files compressed with the Microsoft codec.
   
   For this reason I would welcome an alternative. And there are good alternatives from a technical point of view - e.g. DivX - BUT: 
    
3. To be able to use a codec it has first to be installed. In many cases the codec is free to use for decompression, but to be able to install it you will need permission to install programs on your computer. It is very common that this permission is removed on computers at work, while updates of the Microsoft software is still allowed and maintained. There might be many good reasons for not allowing end users to install programs on computers at work - it might open the computer for virus or trojan horses, games and other stuff that might not be part of the work might be installed, and it might make the computer unstable.
   
   On computers at home these restrictions do normally not exist, but instead lack of knowledge or time might limit the updates. Another problem at home might be that slow internet connections can make the updates time consuming.
   
   If a new Microsoft codec is needed but not present, the user might however be notified by the Microsfot software and have just to click to accept the update, while that does not happen for the more interesting competing alternatives to Microsoft.
    
4. If you have a program that can play video, and a codec associated with this to decompress it, there is still one possible obstacle - the transfer of the media contents to your computer. As previously explained video is very demanding. Also a very short video with limited quality can easily use 1 Mb. When using dialled lines it can in worst case take ten  minutes to transfer a such file. At work video contents might be blocked to protect the internal network and computers. If you have problems playing video at work but believe you are allowed to do so, ask the IT Support if video files are blocked by the company's firewall.
    
5. Also when a video can be played on the computer, I have understood that it sometimes matters how the video is initiated. This can be done by playing the video directly in the browser, or by opening the media player by clicking on a link, or by opening it directly from a media player. If one method does not work, it might be a good idea to try another. On several places in the dance reports the video can be played both in the browser and by clicking on a link. If you want to open the video from a media player, you need to find out the address to the file. This can often be visible in the status line in the browser - otherwise it might be viewable by right clicking the file and then choose Properties.
    
6. If all these things have been solved, it might anyway be problems. One possible problem might be that old computers can not handle the video or the sound.

Below there are some examples of a very short video compressed with different compressing techniques. If you have problems with video, it might help to try them. The files have been kept at a similar size - about 200 kBytes, to make the efficiency of the compression viewable.

1. Uncompressed

The image size has been decreased to just 52 x 39 pixels to make it fit within 200 kB. This sequence, as all others except the DV at the bottom, has no sound and contains 34 frames (a little more than one second). No codec is needed to play this file

http://dansglad.se/videor/codec_uncompressed.avi

2. Cinepak

This is an old codec that might work also on old computers. It is rather inefficient, and has the image size of 160 x 120.

3. Intel Indeo

There are plenty of compressing programs available. Here is one example from the middle category. The image size is 280 x 208.

http://dansglad.se/videor/codec_indeo.avi

4. Windows Media 9

This encoder gives the most efficient compression among those compared here. To be able to play this, it might eventually be needed to install Media Player 9, and at least to install the codec if the notification about this appears. It can probably also be downloaded from www.microsoft.com.

The image size is 640 x 280,. and despite this the file size is a little smaller than those above.

http://dansglad.se/videor/codec_wm_pal_1024.wmv

5. DV - original quality

The source to the videos in Dansglädje can be the simpler digital cameras or as in this case mini DV. The sequence shown above has 34 frames, with a playing time of a little more than one second.

DV has full TV quality, and has a fixed compression giving about 3 MB per second including stereo sound. Within 200 kB it is only possible to include one single image with sound, that is 1/25 second, with the European format PAL (720 x 576 pixels). To be able to play this, a codec for DV is needed.

http://dansglad.se/videor/codec_dv_pal.avi

6. One image in original quality

For those not able to play the DV format, one image is here shown stored as a picture for comparison.

Last updated: 2006-12-03

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