We are very thrilled to know that video metrics are available from Adwords API and tried to pull a report with available metrics which is giving following error. The call and error is printed below.
report = {'reportName': 'AdPerformance',
                    'dateRangeType': 'LAST_7_DAYS',
                    'reportType': 'AD_PERFORMANCE_REPORT',
                    'downloadFormat': 'CSV',
                    'selector': {
                        'fields': ["AdGroupName","AdGroupId",
                            "CampaignId", "AccountDescriptiveName",
                            "Impressions", "CampaignName",
                            "Clicks", "Cost", "AdGroupId", "AdGroupName",
                            "AdNetworkType1", "Date", "Status",
                            "VideoQuartile100Rate", "VideoQuartile75Rate",
                            "VideoQuartile50Rate", "VideoQuartile25Rate",
                            "VideoViews", "Conversions"
                        ]
                    }
                }
Same applies to other reports like Campaign Performance Report.