While their V2.0 firmware added some interesting new features related to different aspect ratios, they've now finally released version 2.2, which adds true 4:3 anamorphic at a resolution of 3328 x 2496, which uses the entire height of the 4:3 sensor. We talked with Panasonic about this during NAB just last week (this new firmware update does not include V-log):
Here's more on the HDMI behavior from the PDF of version 2.2:
About the HDMI output during recording when using [Anamorphic (4:3)]
- The HDMI output cannot be used during recording when [Bit Mode] in [HDMI Rec Output] is set to [4:2:2 8bit].
- If you use the HDMI output when [Bit Mode] in [HDMI Rec Output] is set to [4:2:2 10bit], black bars appear on the right and left sides of the image. As a result, the image will appear on the screen in a smaller size (2880k2160). In addition, you cannot record motion pictures while using the HDMI output.
Though they are in different leagues as cameras, the GH4 actually can now record in an anamorphic resolution very similar to the ARRI ALEXA in Open Gate mode (which is 3.4K). It should be noted as was said above that this will give you a 1.33 (4:3) aspect ratio, which when shot with a 2X anamorphic lens gives you 2.66:1 for an aspect ratio. This would then need to be cropped slightly if you want a more standard 2.39/2.40:1 ratio. It will need to be desqueezed in post either way to view back properly (or on a monitor or recorder that is capable).
You can find the new firmware over at the links below.