Rocket Transcoding Dips

[Cody Cuellar]

I finally installed a Red Rocket card into our Mac Pro Tower and was running some test. The results are a little confusing to me. Our system has 12GB of ram, and all the media I'm working with lives on a three drive striped RAID which gets around 200 MB/sec for HDD speed tests. The rocket is very impressive during 4K realtime playback and 5k full debayer and half-res playback, but during transcodes, it seems like it is limited. At first I was having an issue with RedCine telling me the card was installed on a 2x PCI slot, even though it was installed on slot-2 (8x). I then tried various configs and realized the Decklink SDI card was causing issues until I removed it from the tower. After pulling it, the Rocket registered as a 8x connection and all was good. I then tested various settings for 1080p outputs using clips that were both 2k and 5k from our Epic. No matter the debayer settings or output resolutions (to eliminate software scaling) I seem to be only getting realtime or slightly slower transcodes. I did a job recently and was getting about 18fps transcodes in Davinci on a 1080 project from 4k source footage from the Red without a Rocket (I only have one ATI 5770 card). Davinci seems to output faster than Redcine without a rocket or using Redline. Since redline doesn't support using the Rocket to my knowledge, I have no way of increasing the speed. What I'm wondering is why the rocket can buffer a 2k clip way faster than it plays, but during transcodes it barely gets realtime performance? Also, when testing in Resolve, the transcode plays out realtime, then dips to 0fps for a second, then picks back up for a few seconds and dips back to 0. It's not a consistent realtime playback. The same thing seems to happen using redline in Redcine where all processors will chug away for a few seconds then it dips to a halt for a few seconds, and continues the cycle. I need to run some more tests without the Rocket to compare, but has anyone else experienced this and is there any way to get 5k 1/2 debayer or 2k full debayer to transcode faster than realtime in any program? I feel like if the Rocket can do 4k realtime, I should get 2k MUCH faster, but I can't seem to...

[Nick Shaw]

What I'm wondering is why the rocket can buffer a 2k clip way faster than it plays, but during transcodes it barely gets realtime performance?

I do not know this for sure, but I suspect that the playback buffer in REDcineX is only 8-bit, as that is all that can be displayed on the computer monitor. For final rendering a higher precision would be used, meaning slower rendering.

Speculation again, but this may also be a factor in the dramatic increase in render times when post effects are switched on. An 8-bit image would be sufficient to be passed from the Rocket to the CPU if it is just meant to be displayed "as is" but if it is going to be processed further then a higher precision might be used.