yuy2 frames

I have a usb webcam that outputs yuy2 frames in various screen sizes is there a way to display a yuy2 frame?

Have an IPcam that outputs such a stream of yuy2 frames via LAN…
I can pick the stream. Both mplayer and ffplay can handle. For a stream the best way is to take the link to the stream in a playlist file and the playlistfile to the player. Working fast…
If I take the link to the player outsite a playlistfile to player it takes any time/minutes before the frames are displayed.
If I record a dump from stream, i have to set the filetyp to avi.

Ah good… Its a usb camera. I should at least be able to dump some frames to disc and set the type to avi. If I do that how does the avi file know the frame size? It appears I have the option to stream different frame sizes. I just want to test if the changes I made to get USB Audio working work for USB video.

If I do that how does the avi file know the frame size?

AVI is not a format. It is a wrapper, like mp4 or Matroska.

The file, if a legitimate AVI, will begin with a header which ought to be at (IIRC) offset +32 in the file. This will define the size, speed, scaling, codec, etc etc.

To be a legitimate AVI file, the start (in Zap etc) should be “RIFF....AVI”, where the ‘.’s are bytes. You’ll be able to find the spec online.
If it doesn’t begin with this, it’s not an AVI.

Additionally, as the file is a container, there’s no guarantee that something will be capable of playing the video. Typically the smaller/cheaper webcams use some version of MJPEG, but not necessarily with a colour encoding known to man…
[experience: two cheap cameras, one with everything in shades of green, and one with totally random colours that gave an okay looking picture if rendered in black and white but gibberish in colour]

I’ve noticed that VLC will have a crack at trying to play files with damaged/missing headers by trying to work out what the data actually is (video tends to be chunk based). This may or may not work. Or it may or may not work correctly. ;-)
[experience: my PVR would sometimes fail to write the MP4 TOC and header, VLC did manage to get bits of it (including correctly working out the frame size, impressed!) but not enough to be watchable]

is there a way to display a yuy2 frame?

A quick search online suggests: ffmpeg -i raw.yuv -c copy -pix_fmt yuyv 422 frame%05d.bmp which will accept a raw video input in yuyv colourspace and output a series of BMP files (which are natively r,g,b).

To do it manually, you’ll need to Google to find out what the YUYV format looks like at byte level. If it is 422, then it will be laid out as YUYV in memory, with the first pixel being made up from YU.V and the second being .UYV (that is to say, the first Y being the first pixel, the second Y being the second pixel, and the U and V belonging to both pixels). I’ll leave it to somebody smarter to work out how to change YUV into RGB (or cheat and ask ColourTrans? ;-) ).

Just my €0,02.