video size and bitrates

Blog post edited by Anonymous - "Migrated to Confluence 4.0"

A question that comes up in my research periodically is how much hardware is needed to store and transmit video data? Generally, I get away with the off- the-cuff estimate of 1 hour of video needing 1GB of space. Recently, I needed some better estimates for a proposal so I did some quick digging. The following table (found here) is a starting point to estimate file sizes and bit rates for MP4 files.

Output size, Bitrate, FileSize
320x240 pixels, 400 kbps, 3MB / minute
480x270 pixels, 700 kbps, 5MB / minute
1024x576 pixels, 1500 kbps, 11MB / minute
1280x720 pixels, 2500 kbps, 19MB / minute
1920x1080 pixels, 4000 kbps, 30MB / minute

My 1gb/hour estimate doesn't specify the resolution of the video, the audio content, the compression algorithm used, nor how much change is occurring in the video (which affects the amount of compression that can be done). Using the table above, we can see that 1gb/hour comes out to a file size of about 17 MB/sec, which is about the middle point in the table - making my original 1gb- per-hour-of-video estimate fairly reasonable.

Based on this table, a single camera could easily generate between 4GB and 43GB of data per day. Many research projects gather data using systems of multiple cameras with data piped directly into a computer.

For example, I am working on one (small) project that has two cameras, each running about 5 minutes for three trials a day. While this initial setup only generates about 510MB of data per day, we would like to eventually expand the system to 5 cameras, generating about 1GB of data per day. If we also wanted to process the data "in real time" (i.e., as quickly as possible), then we would need to maintain a transfer rate of around 10MB/second. Even if we bought high-end cameras, our transfer rate would probably top out around 20MB/second when using five cameras for this project.

This type of estimating is useful when writing proposals or designing experiments, because it gives a realistic idea of the type of network that will be required to handle the data transfer in “real time.”

• Dirk

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