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  • Monday, 21 November 2011

    Three steps to get video files NVivo 9 ready

    Written for researchers importing video into NVivo 9.

    In my assistant researcher role for the Student ICT Access and Use project, I must ensure that the diverse video file formats and file sizes used to record student and researcher interviews are usable in NVivo 9.2. This is done in three steps; 1. consistent file name use, 2. compatible file conversion and 3. file re-sizing:

    Step 1. Consistent file names
    It is important for ease of reference and searchability that filenames are accurately and consistently named. For example, video files of the first interview were named according to the following format: (first name) interview (number = one) (date of interview DD Month YYYY).
    • The choice of a first name protects the research subject's privacy; whilst not over-complicating the researcher's codings for subjects.
    • Researchers conducted several interviews with each subject and these need to be distinguishable.
    • Wherever possible, the date of interview should be added to ease citation for research articles.
    Step 2. Video files must be compatible with NVivo 9
    All file formats must be NVivo 9 compatible and I decided to use mp4 as the optimal format for compression. NVivo9 only imports .mpg, .mpeg, .mpe, .wmv, .avi, .qt, .mov and .mp4 files, so I converted all files that were not compatible (i.e. .mts and .flv) to mp4.

    Step 3. Video file sizes must be less than 40 MB to be NVivo 9 import-friendly 
    Interestingly enough, videos created by the best resourced researchers posed the most problems for getting the files NVivo 9 ready: researchers at the University of Fort Hare and Rhodes University used their mobile phones to record the interviews that were in Windows Media Audio/Video File format and these were seldom over 20MB in size. This contrasted to up to 1GB in file sizes being generated by those "better" equipped!  

    The University of Cape Town (UCT) and Free State University (UFS) researchers used high fidelity settings to record their interviews. However, there was no reason for file sizes to be so large; high resolution video or high fidelity sound has no (or minimal) benefits for our analysis.

    Changing filenames was easy, but steps 2 and 3 presented varied challenges and involved using different video compression software to encode the files at lower video resolution and audio fidelity. I have documented processes to overcome these challenges for other researchers, below:

    Problem  #1 with UCT interviews number one: WMV files too big.
    Actions taken to reduce the size of WMV videos:
    1. Did an internet search and found a guide at: http://www.ehow.com/how_5620360_reduce-wmv-file-size.html;
    2. Downloaded AVC video convertor for Mac at http://www.any-video-converter.com/products/mac_video_converter_freeware and installed it;
    3. Changed its output directory to match that of the import directory;
    4. Selected Customised MP4 Movie as the output selection;
    5. Selected one file to encode and export;
    6. Defined the "profile" settings to reduce; the video frame rate to 8, video bitrate to 192, audio bit rate to 32 and sample rate to 8000. Changed audio channel to 1. 
    7. File was then encoded, reducing from 180 MB to 43 MB.
    6. Imported the file as external source into NVivo 9 and it played successfully.
    N.B. The "profile" definitions for the desired export are specified for each file individually; it was more efficient to work on one file at a time.

    Problem #2 with UCT interviews number one: MTS file format is not NVivo 9 compatible and is too large
    Actions taken to change the MTS file format and reduce it size:
    1. Downloaded the free MTS convertor from http://www.mtsconverter.us/ and installed it on Windows 7.
    2. Selected the export option: MPEG-4, 786 kbps, Audio: MP3, 96 kbps. This took 1hr and 20 minutes and the file size was reduced from 837 to148MB.
    3. As this is a free version of the convertor, by default it added the AVS Video Convertor watermark to the middle of the image. Fixing this will cost $59 (before the 30th of November, 2011): the price of unlimited AVS4YOU.com software use.
    4. I then used AVC video convertor to reduce the file's size.
    5. MTS convertor allows for advanced encoding options, so I used the settings from #1.6 on a 1GB video and it was reduced to 52.4 MB. This process only took 25 minutes.

    Problem #3  and #4 with UOFS interviews number one: Interviews in .FLV and .AVI format and too large
    Actions taken to change the FLV and AVI file formats and reduce their file sizes:
    1. I used Any Video Convertor to convert both file formats to MP4 and used the profile settings to reduce the file sizes.

    The next step is to check that all the newly encoded files can be imported into NVivo 9; balancing file size with losses to video and audio quality... and that'll be the subject of my next blog post!

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