lab.lukesturgeon.co.uk

Working with rich-media I have obviously needed to work with video and more specifically flash video, I have been trying to find out more and more about how to squeeze every last pixel of quality from a file whilst keeping the file weight to a minimum.

I discovered a fantastic selection of articles on adobe.com written by experts within the field. After reading through and noting points from as many articles as possible I am trying to collate the information in to a series of “best practise” bullet points for quick and easy reference. I will be using these points when I work with flash video in the future and adding extra sections whenever I discover new information.

Encoding Flash Video (Tom Green and Scott Fegette)

I tried to split the best practises in to headed sections and give a few key points for each section:

Raw footage:

• Mac -> use Quicktime video or Quicktime Animation codecs
• Windows -> use the uncompressed AVI codec

Framerate:

• Streaming video can actually be stream at a lower framerate without a noticable loss of quality
• Original (NTSC) 29.97/30fps -> new 15fps
• Original (PAL) 25fps -> new 12fps

Bitrate:

• Think of bitrate as the current/flow of data coming from the video file, the greater the bitrate the stronger the current, which can cause problems for people with slower connections. Reduce the bitrate reduces the amount of data that is streamed from the video file
• Intranet -> 400 - 600
• Broadband -> 200 - 300
• Diual-up -> 60 - 70

Keyframes:

• A keyframe is similar to a keyframe in Flash, in that it defines a specific point in the files timeline. The frames in-between keyframes are called “difference frames”
• The keyframe interval is how close together the keyframes are to each other, the close the gap the greater the number of keyframes, the greater the quality, the greater the file weight
• If you wanted an interval of 5 seconds between keyframes in a 15fps video file the calculation would be: 15(fps) x 5(secs) -> 75 keyframe interval

Sound:

• The best way to approach sound is to think carefully about the target audience and content of the video
• Audience - most pc speakers are mono, only higher spec systems will have a suitable stereo speakers. Who are your target audience? What spec systems will they generally have?
• Content - a single voice or narration will be fine in mono, movie trailers or video with music will sound much better in stereo