[Video] ffplay uses MJPEG format to play USB camera

0、ffplay About V4L2 Related parameters of

V4L2 indev AVOptions:
  -standard          <string>     .D...... set TV standard, used only by analog frame grabber
  -channel           <int>        .D...... set TV channel, used only by frame grabber (from -1 to INT_MAX) (default -1)
  -video_size        <image_size> .D...... set frame size
  -pixel_format      <string>     .D...... set preferred pixel format
  -input_format      <string>     .D...... set preferred pixel format (for raw video) or codec name
  -framerate         <string>     .D...... set frame rate
  -list_formats      <int>        .D...... list available formats and exit (from 0 to INT_MAX) (default 0)
     all                          .D...... show all available formats
     raw                          .D...... show only non-compressed formats
     compressed                   .D...... show only compressed formats
  -list_standards    <int>        .D..