Drives

Vizzion's Drives sample application

Vizzion's Drives sample application illustrates a number of considerations when developing an application that retrieves Drive streams from on-vehicle cameras, including retrieval of a drive in pages, and extracting JPEG images from a M-JPEG video.

Retrieval of a Drive in Pages

The maximum number of images that can be returned in one GET /vehicles/{vehicleId}/streams request is 10 images, corresponding to 10 seconds, but many drives are more than 10 seconds in length. This sample application uses the offset parameter to fetch entire drives in pages of 10 images each.

Extracting JPEG Images from a Stream

The GET /vehicles/{vehicleId}/streams method returns an MJPEG video. This M-JPEG can be viewed in popular browsers and video players by setting the realtime property to True. To view and/or save individual images from the M-JPEG, the binary data of the video must be parsed and converted to JPEG images. The format of an M-JPEG video is:

...
--boundary
Content-Type: image/jpeg
Content-Length: 271437

    EXIF:
    DateTimeOriginal 	2022:07:23 15:33:03
    GPSLatitude		43.761971
    GPSLongitude	79.392647
    GPSSpeed		104
    GPSImgDirection	70


--boundary
Content-Type: image/jpeg
Content-Length: 272192

    EXIF:
    DateTimeOriginal 	2022:07:23 15:33:04
    GPSLatitude		43.762058
    GPSLongitude	79.392311
    GPSSpeed		104
    GPSImgDirection	71
                                        

This sample application searches the binary data for "Content-length", reads the specified number of bytes, uses the bytes to construct a JPEG image, and repeats the process until there are no more JPEG images.

Extracting EXIF from Images

Each image contains EXIF tags detailing the time, location, speed and heading of the image. This sample app shows how to extract the DateTimeOriginal tag (0x9003).

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