They say they can already control the bit-rate, but only at high ISOs. That's weird. Anyone understand that one?
The bitrate maxed out at 151Mbps at ISO12800, if using normal ISO like 100-400, even if we change the H264 parameter to the highest value possible, there is no obvious increase in bitrate, around 47Mbps in ALL-I, 32Mbps in IPB.
So there is no work around the H264 codec? Why are their block artifacts in ALL-I, if not for insufficient data?
I think the block artifacts is caused by the decoder, 5D3 ALL-I mode uses H264 High Profile at Level 5.1, which is a very advanced and relatively new H264 standard (it supports 4K), thus it requires complex decoding, which might result in blocks in some applications. I use Cineform all the time and haven't noticed any similar thing in my work flow.
As a reference, all previous EOS DSLRs use H264 Baseline Profile at Level 5.0, and 5D3 IPB mode uses H264 High Profile at Level 4.1.
151Mbps at ISO12800 is mostly noise I think. Canon implemented VBR on 5D3 and placed a cap on max bitrate, currently we were able to remove the cap so bitrate can go very high. The next and the key step is to somehow achieve a high bitrate CBR.
According to BBC broadcast specifications, interframe compressed footage should be at least 50Mbps, intraframe compressed footage should be at least 100Mbps, 5D3's 33Mbps and 90Mbps is just a tad below that minimun requirement, how smart Canon is!