Introduction: Good quality of cardiopulmonary resuscitation (CPR) provided by bystanders is important for the outcome in out-of-hospital cardiac arrest (OHCA). A live video stream from the bystander’s smartphone to the medical dispatcher might improve the quality of chest compressions performed during CPR. Methods: At the Copenhagen Emergency Medical Services in Denmark, the medical dispatcher can add a live video to the emergency call. In case of OHCA, the medical dispatcher guides bystanders in dispatcher-assisted CPR (DA-CPR). After initiating chest compressions, the medical dispatcher can add live video streaming. A cohort study was conducted with an evaluation of performed chest compressions from the video footage before and after the dispatcher used the video to instruct CPR (video-instructed DA-CPR). Correct chest compressions were defined according to European Resuscitation Council Guidelines. Results: CPR was provided with a live video stream in 52 OHCA calls, in which 90 bystanders performed chest compressions. Thirty OHCA occurred at a public location, and more than four bystanders were present in 32 (62%) cases. In 26 cases, chest compressions were performed by more than one bystander. Eight (9%) bystanders performed correct chest compressions before video-instructed DA-CPR. For the bystanders first initiating insufficient CPR improvements were observed for: hand placement 58% (n=17/29), compressions rate 73% (n=17/21), and compressions depth 62% (n=19/31) following video-instructed DA-CPR. For the second bystander providing CPR (n=26) improvements were still observed for: hand placement 57% (n=4/7), compressions rate 73% (N=8/11), and compressions depth 53% (n=11/21) following video-instructed DA-CPR. For the third and fourth bystander (n=10), providing CPR improvements were seen for: hand placement 100% (n=2/2), compressions rate 50 % (n=2/4), and compressions depth 60% (n=3/5). Eighteen bystanders had a chest compressions performance measurement that could not be observed. Conclusions: A live video from the bystander`s smartphone to the medical dispatcher could improve the quality of chest compressions in CPR, and guidance seems important not just for the first bystander but for all bystanders performing CPR.