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Streaming Video: Rip & Convert

Tips and tricks for better quality in Streaming Video

Ripping from DVD

WHAT IS VIDEO RIPPING?

"Ripping" is the process of extracting a video program from a DVD and storing it as a computer file in a commonly recognized video file format such as .flv, .mov, .mp4, or .wmv. Different programs provide different choices for managing the ripping process, and these settings will determine the file format, the default height and width of the video, how audio tracks are formatted, and the bit rate (data density) for both the audio and video portions of the program. These factors together will determine the total size of the generated file, how much network bandwidth is needed to stream the video, and the display quality.

VIDEO QUALITY AND FILE SIZE

Streaming video requires a balance between file size and quality. A larger file will produce a clearer picture that can be scaled to produce an image of almost any size, but will take up more room on the video server and will take up more network bandwidth during streaming. A smaller file will take up less room on the server and will impact the network less during streaming, but the video display is likely to be blurry, fuzzy, or pixelated. 

The balancing point may be different for different films. A video with a great deal of visual detail or rapid action may require a higher data density, for example. A video with relatively simple imagery and slower changes between scenes, such as a video produced from a PowerPoint presentation, may work well with far less data per video minute.

Just as a rule of thumb, OnStream, Loyola's streaming service provider, recommends the following bit rates:

Rule-of-Thumb Bitrates
WIDTH HEIGHT BIT RATE
480 270 400-500 kbps
640 360 500-750 kbps
960 540 800-1500 kbps

These are just estimates and should not be taken too literally.

Setting bit rates is a feature many ripping programs provide, but it can be difficult to anticipate what the resulting file size will be for a given DVD and bit rate selection (this is partly due to how the video is compressed, which varied by file type). Depending on the program used, it might be easier to set some of the video parameters such as height and width, set the type of audio to be used, and then specify a target file size. Given those data, some programs determine the bit rate automatically.

SOME SUGGESTED GUIDELINES

Results on any single video program may vary, but some suggested (not required) guidelines for balancing quality with file size and bandwidth requirements are listed here.

VIDEO WIDTH (640)

If the video on the DVD has a display width larger than 640, reduce the width either to 640 or whatever option the program offers that is close to 640. This will reduce the size of the resulting file. The online player displaying the video can up-convert to a larger width if desired. It might seem counter-intuitive to reduce the file from DVD then up-convert on display, but since the up-convert can usually be handled by the online player program on the client side, this actually saves storage space and network bandwidth.

While selecting a smaller video width, it is important to avoid changing the aspect ratio (width to height) of the program. It is important to know if the width and height options offered by a particular ripping or converting program automatically respect the aspect ratio of the source or if the aspect ratios need to be checked manually for agreement. Manually shifting height or width settings in a way that alters the aspect ratio may stretch or squash the image in one dimension or the other, or may introduce black bars (unused video space) permanently into the video file.

FILE SIZE (450 MB/Program Hour)

With many ripping programs, it is easier to change the target file size for the output file than to try to adjust the bit rate. The program will likely set the bit rate to whatever is required to achieve the specified file size. Some suggestions are:

  • If the video program is much more than two hours long, it should probably be divided into separate files
  • Generally, set the file size for about 450 megabytes per video program hour.
  • For programs near 2 hours in length, set the file size or 900 to 950 megabytes (keeping the output file under 1 gigabyte)

BIT RATE

  • If the ripping program in use does not support selecting the output file size, it might be necessary to set the bit rate to one of the values suggested above. 

AUDIO TYPE SETTING (Stereo or Mono)

  • If the DVD provides only Monaural or basic Stereophonic sound, the ripping program will probably set the audio output either to Mono or Stereo accordingly. These values should not be changed.
  • Many DVDs now carry audio tracks in varieties of surround sound that require more than 2 channels. Retaining these kinds of audio tracks in the ripped file is a waste of space and bandwidth because few online video players can render sound in anything other than Mono or Stereo. If the video output type shown in the ripping program appear to be anything other than Mono or Stereo, set it to Stereo. This will reduce the output file size.

CONVERTING

In some situations a video program already exists as a video file on a computer, and has to be converted from one format to another to be made available for streaming. For example, Microsoft PowerPoint on a Windows PC generally saves slide presentations only in the .wmv (Windows Media Video) format, which has to be converted to .flv (Flash Video) for streaming. 

Video conversion programs, such as Adobe Encoder or Freemake Video Converter, provide many of the same options as ripping programs, and the same considerations described above apply. Key considerations are:

  • Set video width, file size, and audio type as described for ripping programs, above.
  • Avoid altering the program's aspect ratio
  • Remember that the best a conversion program can do is retain the video quality of the input file. If the conversion is done with the right settings but the converted output is poor, it may be necessary to re-rip the program from the original DVD or otherwise get a higher quality version of the video for input to the conversion process.