After two weeks with the Panasonic Lumix GH4 we have finally put the variable frame rate VFR mode through it’s paces and explored every setting for strengths and weaknesses. See video below:
First off the bat we found that the quality loss from true 1080p was not as bad as feared and looked closer to an in between quality of 720p and 1080p. It does suffer from aliasing and moire that is all too known from Canon owners of 5D mk II, 7D, Rebels,60D and 70D and Nikon on most of their cameras except for the latest 6000 series which are very clean.
The 96fps mode does look soft compared to the punchy detail of in Camera 1080p and mushy compared to the 4k mode. However it is very usable if you avoid heavy detail like diagonal, vertical and textures in wider shots. It is a better performer for people and close ups.
The latest tests on the VFR mode do show a sharp quality decrease above 60p. The 72p, 84p and 96p continue to decrease the bit rate and detail in the footage by dicing the video into smaller data. It seems that the camera cannot encode larger than 100 Mbps at any time no matter what the resolution is. 96p showed a maximum bit-rate of just 22 Mbps peak which is the largest keyframe in the codec. Things start to improve as you lower the frame rate to 84p at 24 Mbps and 72p 28 Mbps. 72p looks better overall with the increased data but it is nowhere close to the 60p mode which seems to not skip lines on the sensor. It still has aliasing and moire at 60p but more subdued. If you need the most quality from the VFR mode you need to shoot in 60p and below.
As the graph above shows the VFR mode restricts even the 60p mode by starving it to just a peak of 35 Mbps which the camera in regular 1080p 60 fps mode has a peak of 96 Mbps. Interesting that the VFR mode kills bitrate in the codec even when using frame rates that the camera supports.
We analyzed the data and found that the reason VFR mode in the 60p range suffers is because it is conforming the footage at 24p. Basically maintaining a 35 Mbit/sec for 24p out of a 60p recording. Which is the same 100 Mbps limit of the camera when shooting at regular 60p mode. We found however than even if the bit rate was equivalent, you are better off shooting 60p regular mode at 1080p because it will retain detail better. There is a very slight softening of the image however small by the conforming process. Also the EX Tele mode is not disabled in the 60p regular mode.
We can’t help but feel that the restricted encoder at 100 Mbps is holding the camera back. Considering 1080p can shoot at 200 Mbps in camera at its highest setting the dicing of the VFR mode data could be essentially doubled by a hack. If hacked the camera should be able to encode 192 fps at the same 22 Mbps max of the current 96fps mode. It should increase detail and reduce artifacts in the footage.
Ideally a hack should be able to liberate the camera and allow it to record at 200 Mbps in VFR mode. Having bit rates available doubled and maybe increase frame rates at lower bit rates. If the limit is not hardware based, this could become the most desirable hack for the GH4. Furthermore the 720p mode could do amazingly high frame rates with this data essentially doubling the speed capabilities. This however would be much harder as the AVCHD mode in 720p is not connected to VFR mode.
In the end VFR mode can deliver fairly good quality but with bit-rate restrictions. The potential for using the full 200 Mbps mode is in there but it will be a matter of some very clever people doing a miraculous hack to liberate these higher settings. The camera can encode 200 Mbps in 1080p mode, the power is there at least to increase the VFR mode bit rate. That the regular 60p mode in camera looks better than the VFR 60 fps setting shows that the VFR mode is probably a completely independent code branch for the encoder. It is in it’s own mode.
The GH4 retains the bronze #3 spot in our HSC affordable camera guide. We can’t wait to see what hackers will be able to do with the camera once the firmware is available.
See our first video test of 96fps here:
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