Editing Question for Clarity Thanks for feedback so far, very insightful.
I'm not sure how far along this part of the software community is, and what if any libraries exist for me to leverage from. Heres what I'm trying to do.
Problem: Take an existing video of a game of rugby league. The Rugby League field is 100 metres long, 70 metres wide, and has white line markings every 10 metres running along the width of the field, as well as along the sidelines. Each side has 13 players on the field. Players on each team have identical jerseys that normally constrast strongly against background colours (green/brown field colour) and the referee's colour (usually yellow) and the designated water runner (orange). All players have a unique number in thick white lettering on their backs for identification. Video is taken with a high definition camera. Currently only one camera is used (2D) and existing video does not contain a foreground object of fixed spatial dimensions (as suggested in one answer for comparision measurements, however I could add this to future filming sessions if it is worthwhile). The player's do not run in a straight line 50% of the time but will go sideways on on a diagonal to the play the ball. The distance measured always starts from the spot of the previous "tackle", which ends where the player stops forward movement. It is not always possible to determine the players number from the video (facing other direction, sunlight, others standing in the way of the camera). But this isn't important as the software could allow for manual inputting of unknown "runs" at a later point after analysis.
Determine the distance between two points (i.e. where the player started his "run" and where he finished it).
I'm guessing that this would be quite doable if I manually marked the start and end point in the video. But how would I use landmarks in the background to determine the distance (assuming the person taking the video has kept it from jerking around).
Question: Do software packages or libraries exist that are specialised enough to assist with writing analysis software to determine a sports persons distance travelled based on video taken of the performance?