THE XAVC CODEC FAMILY
The XAVC family of codecs was introduced by Sony back in 2014. Until recently all flavours of XAVC were based on H264 compression. More recently new XAVC-HS versions were introduced that use H265. The most commonly used versions of XAVC are the XAVC-I and XAVC-L codecs. These have both been around for a while now and are well tried and well tested.
XAVC-I
XAVC-I is a very good Intra frame codec where each frame is individually encoded. It’s being used for Netflix shows, it has been used for broadcast TV for many years and there are thousands and thousands of hours of great content that has been shot with XAVC-I without any issues. Most of the in flight shots in Top Gun Mavericks were shot using XAVC-I. It is unusual to find visible artefacts in XAVC-I unless you make a lot of effort to find them. But it is a high compression codec so it will never be entirely artefact free. The video below compares XAVC-I with ProResHQ and as you can see there is very little difference between the two, even after several encoding passes.
XAVC-L
XAVC-L is a long GOP version of XAVC-I. Long GoP (Group of Pictures) codecs fully encode a start frame and then for the next group of frames (typically 12 or more frames) only store any differences between this start frame and then the next full frame at the start of the next group. They record the changes between frames using things motion prediction and motion vectors that rather than recording new pixels, moves existing pixels from the first fully encoded frame through the subsequent frames if there is movement in the shot. Do note that on the F5/F55, the FS5, FS7, FX6 and FX9 that in UHD or 4K XAVC-L is 8 bit (while XAVC-I is 10 bit).
Performance and Efficiency.
Long GoP codecs can be very efficient when there is little motion in the footage. It is generally considered that H264 long GoP is around 2.5x more efficient than the I frame version. And this is why the bit rate of XAVC-I is around 2.5x higher than XAVC-L, so that for most types of shots both will perform similarly. If there is very little motion and the bulk of the scene being shot is largely static, then there will be situations where XAVC-L can perform better than XAVC-I.
Motion Artefacts.
Broadcasters and organisations such as Netflix spend a lot of time and money testing codecs to make sure they meet the standards they need. XAVC-I is almost universally accepted as a main acquisition codec while XAVC-L is much less widely accepted. You can use XAVC-L if you wish, it can be beneficial if you do need to save card or disk space. But be aware of its limitations and avoid it if you are shooting handheld, shooting anything with lots of motion, especially water, blowing leaves, crowds etc. Also be aware that on the F5/F55, the FS5, FS7, FX6 and FX9 that in UHD or 4K XAVC-L is 8 bit while XAVC-I is 10 bit. That alone would be a good reason NOT to choose XAVC-L.
All good points when it comes to image quality and motion.
I’m curious if you’ve noticed any difference between XAVC-I and XAVC-L when it comes to editing and the load it puts on your NLE and computer? I’ve noticed that XAVC-L sometimes doesn’t play as smoothly perhaps because the complexity of decoding the long GOP structure is more compute intensive vs. intra frame compression.
I’ve found that on F5/F55, the XAVC-L codec option is only available in HD resolutions (1920×1080). UHD and 4K is always XAVC-I. (Operating Instructions p.6: https://pro.sony/ue_US/support-resources/pmw-f55/manual) So an advantage of newer cameras like the FS7 is that you have the option to record in XAVC-L at higher resolutions of 4K.
Long GoP codecs are more complex to decode than I only codecs, so XAVC-L will require more processing power than XAVC-I. But most recent computers now include hardware decoding for H264 (and many now also include H265) so this is generally much less of an issue than it used to be.
I had forgotten about all the XAVC-L limitations in the F5/F55, it was only added late in the cameras life (version 9 firmware). It’s been a long while since I used mine.
Hi
Is the choice effecting the SDI and HDMI signal?
TNX
/ Jonas