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Screenshot taking is an offline task that takes screenshots of a video at specified times. VOD supports the following types of screenshots:

• Time point screenshot: Takes screenshots at specified time points.
• Sampled screenshot: Takes screenshots at regular intervals.
• Thumbnail: Takes a screenshot at a specified time point and uses it as the video’s thumbnail.
• Image sprite: Takes multiple screenshots at the specified interval and combines them into one image (image sprite).

Common use cases include the following:

• Video thumbnail generation: Take a screenshot of a video and use it as the video’s thumbnail.
• Image sprite generation: Generate an image sprite (a collection of small images), which is often used as the summary of a video.
• Preview: Use image sprites and VTT files to show previews above the progress bar.

Screenshot Templates

A screenshot template is a collection of screenshot parameters, including the output file format and image dimensions.

Time point screenshot templates

You can use a time point screenshot template to take a screenshot at a specific time point or generate a thumbnail.

VOD provides preset time point screenshot templates for common parameter combinations. You can also create your own templates and manage them in the console. For details, see Template Settings.

Sampled screenshot templates

You can use a sampled screenshot template to take screenshots at regular intervals.

VOD provides preset sampled screenshot templates for common parameter combinations. You can also create your own templates and manage them in the console. For details, see Template Settings.

Image sprite screenshot templates

You can use an image sprite screenshot template to generate image sprites.

Note：

• The result of multiplying Width x Columns (i.e., sprite width) should be within the range of 128-4096.
• The result of multiplying Height x Rows (i.e., sprite height) should be in the range of 128-4096.

VOD provides preset image sprite screenshot templates for common parameter combinations. You can also create your own templates and manage them in the console. For details, see Template Settings.

Initiating a Screenshot Task

You can initiate a screenshot taking task by calling a server API, via the console, or by specifying the task when uploading videos. For details, see Task Initiation.

Specifically, you can initiate a screenshot task by doing one of the following:

• Call the server API ProcessMedia, specifying the ID of the screenshot template in MediaProcessTask.SnapshotByTimeOffsetTaskSet.
• Add a task flow in the console, specifying the screenshot parameters, and use the task flow to process videos in the console.
• Add a task flow in the console, specifying the screenshot parameters. When uploading a video from the server, set the procedure parameter to the task flow you created.
• Add a task flow in the console, specifying the screenshot parameters. When uploading a video from a client, set procedure in the upload signature to the task flow you created.
• Add a task flow in the console, specifying the screenshot parameters. When uploading a video via the console, choose Auto-processing after upload and select the task flow you created.

Getting the Result

After initiating a screenshot task, you can wait for the result notification asynchronously or perform a task query synchronously to get the task execution result. Below is an example of the notification received in normal callback mode after a screenshot task is initiated (the fields with null value are omitted):

{
    "EventType":"ProcedureStateChanged",
    "ProcedureStateChangeEvent":{
        "TaskId":"1256768367-Procedure-2e1af2456351812be963e309cc133403t0",
        "Status":"FINISH",
        "FileId":"5285890784246869930",
        "FileName":"Animal World",
        "FileUrl":"http://1256768367.vod2.myqcloud.com/xxx/xxx/AtUCmy6gmIYA.mp4",
        "MetaData":{
            "AudioDuration":60,
            "AudioStreamSet":[
                {
                    "Bitrate":383854,
                    "Codec":"aac",
                    "SamplingRate":48000
                }
            ],
            "Bitrate":1021028,
            "Container":"mov,mp4,m4a,3gp,3g2,mj2",
            "Duration":60,
            "Height":480,
            "Rotate":0,
            "Size":7700180,
            "VideoDuration":60,
            "VideoStreamSet":[
                {
                    "Bitrate":637174,
                    "Codec":"h264",
                    "Fps":23,
                    "Height":480,
                    "Width":640
                }
            ],
            "Width":640
        },
        "MediaProcessResultSet":[
            {
                "Type":"SnapshotByTimeOffset",
                "SnapshotByTimeOffsetTask":{
                    "Status":"SUCCESS",
                    "ErrCode":0,
                    "Message":"",
                    "Input":{
                        "Definition":10,
                        "Definition":[3, 6, 9]
                    },
                    "Output":{
                        "Definition":10,
                        "PicInfoSet":[
                            {
                                "TimeOffset":3,
                                "Url":"http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx1.jpg"
                            },
                            {
                                "TimeOffset":6,
                                "Url":"http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx2.jpg"
                            },
                            {
                                "TimeOffset":9,
                                "Url":"http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx3.jpg"
                            }
                        ]
                    }
                }
            },
            {
                "Type":"SampleSnapshot",
                "SampleSnapshotTask":{
                    "Status":"SUCCESS",
                    "ErrCode":0,
                    "Message":"",
                    "Input":{
                        "Definition":10
                    },
                    "Output":{
                        "Definition":10,
                        "SampleType": "Percent",
                        "Interval": 10,
                        "WaterMarkDefinition": [],
                        "ImageUrlSet":[
                                "http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx1.jpg",
                                "http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx2.jpg",
                                "http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx3.jpg",
                                "http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx4.jpg",
                                "http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx5.jpg",
                                "http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx6.jpg",
                                "http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx7.jpg",
                                "http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx8.jpg",
                                "http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx9.jpg"
                        ]
                    }
                }
            },
            {
                "Type":"ImageSprites",
                "ImageSpriteTask":{
                    "Status":"SUCCESS",
                    "ErrCode":0,
                    "Message":"",
                    "Input":{
                        "Definition":10
                    },
                    "Output":{
                        "Definition":10,
                        "Height":80,
                        "Width":142,
                        "TotalCount":1,
                        "ImageUrlSet":[
                            "http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx1.jpg"
                        ],
                        "WebVttUrl":"http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx.vtt"
                    }
                }
            },
            {
                "Type":"CoverBySnapshot",
                "CoverBySnapshotTask":{
                    "Status":"SUCCESS",
                    "ErrCode":0,
                    "Message":"",
                    "Input":{
                        "Definition":10,
                        "PositionType":"Time",
                        "PositionValue":0
                    },
                    "Output":{
                        "CoverUrl":"http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx.jpg"
                    }
                }
            }
        ],
        "TasksPriority":0,
        "TasksNotifyMode":""
    }
}

In the above callback, ProcedureStateChangeEvent.MediaProcessResultSet contains four types of results, namely SnapshotByTimeOffset, SampleSnapshot, ImageSprites, and CoverBySnapshot, which represent a time point screenshot task, a sampled screenshot task, an image sprite screenshot task, and a thumbnail generation task respectively.