If you’re seeing choppy video playback on your computer it could be because you are watching a video whose quality is too high for the hardware you’re using to view it. Because of how videos are normally encoded they use a variable bitrate as opposed to a constant bitrate. That means that the amount of data outputted varies each second depending on the amount of movement/action in a particular scene. Or, worded another way, the more that changes between frames the higher the bitrate will be. The higher bitrate ensures that any movement in the video will appear smooth to the viewer.
So how do you determine whether the issues you are seeing are due to high bitrate portions of a video? I use the free VLC video player which includes a video statistics page that will show you the bitrate in real-time as you are watching it. To get to this information go to the Tools menu (Window menu on a Mac), click Media Information, and switch to the Statistics tab. From there you should see all kinds of real-time information about the video you are watching.
You might notice that there are a couple different bitrates that are listed under the Input section: input bitrate and content bitrate (called stream bitrate on the Mac version of VLC). The input bitrate refers to the data that is being passed into VLC, and the content bitrate refers to the amount of data being displayed on the screen at any given point. Generally it doesn’t matter which one of these you really watch, and if you look closely you’ll almost notice a pattern between the two values. The value for the content bitrate should be about the same as what the input bitrate was about one second prior. That means if a high-action scene all of a sudden starts up in the video you might see the input bitrate jump from 8,000 kb/s up to 20,000 kb/s. Roughly a second after that you should see the content bitrate jump to about the same value. So it makes sense if you think of the content/stream bitrate as an output bitrate.
This is some great info when it comes down to troubleshooting video playback issues, and hopefully it might help some of you down the road.