ioctl VIDIOC_G_JPEGCOMP, VIDIOC_S_JPEGCOMP &manvol; VIDIOC_G_JPEGCOMP VIDIOC_S_JPEGCOMP int ioctl int fd int request v4l2_jpegcompression *argp int ioctl int fd int request const v4l2_jpegcompression *argp fd &fd; request VIDIOC_G_JPEGCOMP, VIDIOC_S_JPEGCOMP argp [to do] Ronald Bultje elaborates: APP is some application-specific information. The application can set it itself, and it'll be stored in the JPEG-encoded fields (eg; interlacing information for in an AVI or so). COM is the same, but it's comments, like 'encoded by me' or so. jpeg_markers describes whether the huffman tables, quantization tables and the restart interval information (all JPEG-specific stuff) should be stored in the JPEG-encoded fields. These define how the JPEG field is encoded. If you omit them, applications assume you've used standard encoding. You usually do want to add them. &cs-str; int quality int APPn int APP_len char APP_data[60] int COM_len char COM_data[60] __u32 jpeg_markers See . &cs-def; V4L2_JPEG_MARKER_DHT (1<<3) Define Huffman Tables V4L2_JPEG_MARKER_DQT (1<<4) Define Quantization Tables V4L2_JPEG_MARKER_DRI (1<<5) Define Restart Interval V4L2_JPEG_MARKER_COM (1<<6) Comment segment V4L2_JPEG_MARKER_APP (1<<7) App segment, driver will always use APP0 &return-value;