Most popular media player software are generally unable to playback partial video files and display some sort of error message (example, 2). This tutorial shows you how to start watching videos while the file is still downloading, so you don't have to wait around for it to fully download. Please note this only works when the file you're downloading is not in RAR or ZIP format, but instead directly available in AVI/MKV/MP4/WMV/etc. video format. Step 1 Download and install VLC media player. VLC media player is a free and open-source media player software. If you already have VLC media player installed, skip to Step 2. Once downloaded, run the file. You will be presented with a window similar to the one shown below. The series of five screenshots below walk you through the installation process. Click "Next >". . Click "Next >" again. . Click "Next >" once more. . Click "Install". . Untick the "Run VLC media player ..." checkbox and click "Finish". Step 2 Assuming you're downloading a video file in Mozilla Firefox, you will either see the partial video file by itself, or the video file accompanied with another file with the same filename, followed by ".part". Notice in the screenshot above, the file size of the actual video file is "0 KB", while the .part file's size gradually increases as the download progresses. The .part file is a temporary container that exists only during the download, and disappears once the file has fully downloaded (with its contents transferred to the actual video file). If this .part file does not exist, playing the partial video file is straightforward. Simply double-click the video file with the orange, "traffic cone" icon and it will begin playing in VLC media player. If this .part file does exist, you will need to start VLC media player (double-click the icon on your Desktop) and drag-and-drop this .part file into VLC media player. The animation below demonstrates this. . If the video is an AVI file, you will be presented with a window (as pictured below), that reads "The AVI file is broken. Seeking will not work correctly. Do you want to try to fix it?" Click "Don't repair". The video will now begin playback. Step 3 Firefox "Download Error" If it so happens that when the video file completes downloading, you are watching/playing back (using) the .part file, Firefox will be unable to automatically rename the file to remove ".part" from the filename and will instead display an error message ("... could not be saved, because an unknown error occured."), similar to that pictured below. Click "OK". This is nothing to be concerned about. Firefox is simply saying that it was unable to rename the file because the file was in use (by you). . Remove ".part" from filename after download Once you've finished watching the video: Close VLC media player. Open the folder where the file is located. Right-click on the .part file and select "Rename" from the context menu. Remove ".part" from the end of the filename and press "Enter" on your keyboard. Click "Yes" in the dialog window that reads "If you change a file name extension, the file might become unusable." That's it! Congratulations, you now know how to start watching videos while the download is still in progress. ~~~ Troubleshooting If you can hear audio playback, but cannot see video, maximize the VLC media player window. This should resolve the problem.