Screencapturing is an offline task that captures a screenshot of a video at a certain point in time. VOD provides the following types of screenshots:

• Time point screenshot: VOD can capture screenshots of a video at the specified set of time points.
• Sampled screenshot: VOD can capture a set of screenshots of a video at the specified time interval.
• Cover screenshot: VOD can capture a screenshot of a video at the specified time point and use its URL as the video cover in the media asset management system.
• Image sprite: VOD can capture a set of screenshots of a video (subimages) at the specified time interval and splice them together to generate a large image (i.e., image sprite).

The screencapturing feature can meet your needs in the following application scenarios:

• Video cover generation: a screenshot of a video can be used as its cover.
• Thumbnail: an image sprite is a large image composed of multiple subimages (i.e., thumbnails), which is usually used to represent a video overview.
• Playback preview: together with a VTT file, an image sprite can be used to achieve preview effect on the player progress bar.
  

  Screencapturing Template

The target specification of a screenshot is subject to parameters such as screenshot file format, width, and height, which can be customized in the form of VOD screencapturing template as shown below:

Time point screencapturing template

A time point screencapturing template is used to take a screenshot at a specified time point or take a screenshot as a cover.

For common specifications, VOD provides a preset time point screencapturing template. In addition, you can also create and manage custom screencapturing templates in the console. For detailed directions, please see Template Settings.

Sampled screencapturing template

A sampled screencapturing template is used to take sampled screenshots.

For common specifications, VOD provides a preset sample screencapturing template. In addition, you can also create and manage custom screencapturing templates in the console. For detailed directions, please see Template Settings.

Image sprite generating template

An image sprite generating template is used to take screenshots and combine them to generate an image sprite.

• The value of Width * Columns should be between 128 and 4,096 px (i.e., the range of the image sprite width).
• The value of Height * Rows should be between 128 and 4,096 px (i.e., the range of the image sprite height).

For common specifications, VOD provides a preset image sprite generating template. In addition, you can also create and manage custom screencapturing templates in the console. For detailed directions, please see Template Settings.

Task Initiation

There are three ways to initiate a screencapturing task, namely, directly initiating through server API, directly initiating through the console, and specifying a task upon upload. For more information, please see Task Initiation for video processing.

Below are instructions for initiating screencapturing tasks in these ways:

• Call the server API ProcessMedia to initiate a task: specify the screencapturing template ID in the MediaProcessTask.SnapshotByTimeOffsetTaskSet parameter in the request.
• Initiate a task on a video through the console: add a task flow in the console, set the target screenshot specification in the task flow, and use the task flow to initiate video processing.
• Specify a task upon upload from server: add a task flow in the console, set the target screenshot specification in the task flow, and specify this task flow as the procedure in the ApplyUpload request.
• Specify a task upon upload from client: add a task flow in the console, set the target screenshot specification in the task flow, and specify this task flow as the procedure parameter in the signature for upload from client.
• Upload through console: add a task flow in the console, set the target screenshot specification in the task flow, upload a video through the console, select Process Video During Upload, and specify to execute this task flow upon video upload completion.

Getting Result

After initiating a screencapturing task, you can wait for result notification asynchronously or perform task query synchronously to get the task execution result. Below is an example of getting the result notification in normal callback mode after the screencapturing 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,
                        "PicInfoSet": [
                            {
                                "TimeOffset":6,
                                "Url":"http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx1.jpg"
                            },
                            {
                                "TimeOffset":12,
                                "Url":"http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx2.jpg"
                            },
                            {
                                "TimeOffset":18,
                                "Url":"http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx3.jpg"
                            },
                            {
                                "TimeOffset":24,
                                "Url":"http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx4.jpg"
                            },
                            {
                                "TimeOffset":30,
                                "Url":"http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx5.jpg"
                            },
                            {
                                "TimeOffset":36,
                                "Url":"http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx6.jpg"
                            },
                            {
                                "TimeOffset":42,
                                "Url":"http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx7.jpg"
                            },
                            {
                                "TimeOffset":48,
                                "Url":"http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx8.jpg"
                            },
                            {
                                "TimeOffset":54,
                                "Url":"http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx9.jpg"
                            },
                            {
                                "TimeOffset":60,
                                "Url":"http://1256768367.vod2.myqcloud.com/xxx/xxx/xxx10.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 callback result, ProcedureStateChangeEvent.MediaProcessResultSet contains the result in Type of SnapshotByTimeOffset, SampleSnapshot, ImageSprites, and CoverBySnapshot, which represent time point screencapturing, sampled screencapturing, image sprite generating, and cover generating tasks, respectively.