use yuvj420 (pyav jpeg full range)

[mgineer85]

YUVJ420 is full range jpeg in terms of PyAV.

Executing the example capture_pyav.py gives following output with this change:

<av.VideoStream #0 mjpeg, yuvj420p 1280x720 at 0x7fff7d4a58f0>

<av.VideoStream #0 mjpeg, yuv420p 640x480 at 0x7fff7d4a5b20>
<av.VideoStream #0 mjpeg, yuvj420p 1280x720 at 0x7fff7d4a5b20>

It means, the codec_context is not copied from the encoder, but at least the width/height/pix_fmt seem to be relevant for the output stream to write correct output.

The output file is created with this change as before but not using the range setting but the pix_fmt.

[davidplowman]

Hi, thanks for submitting the PR.

Just one thing we still need to look at. For the legacy platform codecs (so that's the V4L2 hardware encoders on Pi 4s and earlier), the add_stream method doesn't get a codec_context object (because there isn't one), just a string "video" or "audio". So we need to do something a little different there. I think I still have the problem where if the color_range isn't 2, then I don't get an output file at all!

Trying MJPEG out on a Pi 4 again I'm also not convinced that I'm getting full range YUV. I can't make the Y channel (when decoded) go below about 14, whereas I can get zero on a Pi 5. I haven't found out how I can stop that, so there's another mystery there.

And finally (and trivially), we'd need to remove some of those print statements that crept in.

But any ideas on those other points? Thanks!