We have a lot of publishers wanting to post large video files (.flv or .swf) to our web site.
I'm not an expert on videos so I was curious about what I should recommend for file sizes. With the larger use of broadband, I know we can have larger files than before, but does anyone have a recommendation (i.e. keep video files below x MB)? Do either of these file formats stream by themselves, making file size less relevant?
Any help on this would be much appreciated.
The file size of a video is not as relevant to good viewer experience as is the bitrate used to compress the video. Assuming you are using progressive downloading, once the video starts to play, as long as it is not interrupted by the stop..start..stop..start of having to buffer, the viewer experience will be good. Having the video continually interrupted as it download is very annoying and does not make for a good viewing experience.
The bitrate basically describes how fast the flow of data needs to come into the video player (on the viewers machine) so that there is no interruption in the playback. A 50MB video file will play back just as smoothly as a 5MB video file, given the correct bitrate for the Internet connection speed of the viewer. There has been some discussion of problems with progressive downloads once the file size hits 150-200MB, but Iíve not experienced this.
The proper choice of bitrate is related to the quality desired and the physical dimensions of the media player screen. For example, a 320 X 240 video display can produce equal quality video at less than half the bitrate which would be required if the display screen was 480 X 360. Compare the bitrate to a can of paint. A quart of paint might look just perfect if used to cover a 32 X 24 foot area, yet trying to stretch that same amount of paint out to cover a 48 X 36 foot area would leave it thin and would not give good results. Same with video, stretch it (the incoming data stream) out and the quality suffers.
As a guideline, on a 320 X 240 display screen, a bitrate of 250kbps will produce mediocre quality video, while a bitrate of 400 or more will produce good to excellent results. That same video shown on a 480 X 360 display would produce poor quality at 250kbps and only mediocre quality at 400. A better choice would be somewhere are the 750 Ė 800 kbps for good quality.
Biggest problem in downloading high bitrate (500kbps and up) video is the connection speed of the final viewer. Itís not uncommon that the connection speed needs to be 2 or 3 times the bitrate of the video in order to assure uninterrupted downloading. So a 400kbps video should download OK on a 1.5 Mb connection, but thatís about the max. Best bet, test a few videos rendered at various bitrates on several different connection speeds to get a real feel for what your viewers will experience on their end.
Eye for Video
Thanks for the info. I had a feeling file size wouldn't matter as much if it was using progressive streaming, but I didn't know what else to measure by so this is very helpful.
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