What is HDV?
What is HDV?
Director of Engineering
There has been a lot of hype and confusion about the new HDV format that has recently hit the market. Here at Victory Studios, we have been trying to put together some information to help our clients understand this new format. Below is the beginning of a short list of questions that we have been asked lately. We hope that it is helpful to others in the video community.
What is HDV?
HDV is a new recording format that allows for High Definition (HD) footage to be recorded onto standard MiniDV cassettes. Instead of using DV compression, it uses “Long GOP MPEG2” which allows for the higher data compression that is needed to fit HDTV footage onto the same tape at the same data rates. There are currently two versions of HDV, 720P/30 (720 lines, 30 frames per second) and 1080i/60 (1080 lines/60fields per second). The Sony HVR-Z1U uses the 1080i/60 HDV standard.
Can I edit HDV on my existing edit system?
Non-linear edit system manufactures are scrambling to add HDV support to their products. Right now (February 2005) there are very few that have native HDV support, but there are plugins available to allow for editing to be done. HDV support is already included inUlead MediaStudio Pro7 (with additional HD module), Pinnacle Liquid Edition 6, and Canopus Editus. For Vegas 5 and PremierPro 1.5, there are plugins available from Cineform that will allow long-GOP HDV to be translated into a wavelet-based file that can be edited by these programs. Indications are that the Cineform plugins may be included in future versions of Vegas and PremierPro to facilitate HDV editing. Avid has announced support for HDV by “mid-2005” on a number of their products. There are a number of plugins for Final Cut Pro including LumiereHD and Heuris Indie Toolkit and Apple has released naitive HDV support for iMovie and Final Cut Express (now dubbed “iMovie HD” and “Final Cut Express HD”). All indications point to inclusion of HDV support into a new version of Final Cut Prothat will most likely be announced at NAB in mid-April. Using external hardware, Victory Studios has successfully integrated HDV footage into several HD editing systems including Final Cut Pro HD and Avid DS-Nitris.
What is “Long-GOP MPEG2” and why does it make a difference for editing?
Until now, most production video formats for recording and editing have used various forms of “intra-frame” compression. This means that all data for an individual frame is packaged together. Because all information for each frame was kept together so you could take the data for any one frame and view it or edit it independently of all others. Long-GOP MPEG2 is an “inter-frame” compression, which means that data for multiple frames is packaged together. In the case of 1080i HDV, the GOP (Group-Of-Pictures) is 15 frames long. This makes it difficult to view or edit individual frames because you may need information stored in nearby frames to complete the picture. Editing systems need to take this into account to allow for edits to take place at any frame boundary (not just the beginning or end of the 15 frame GOP).
What is “CineFrame-24”?
That is the big question that everyone is asking. As far as we know, Sony has not released anything official, but looking at what the output looks like, this is what we have determined: Cineframe-24 is a way to digitally manipulate a 60i image to produce a “simulated 24P” look. This is how it works: the imager is running at 60i so it is capturing half the total lines of resolution every 1/60th of a second. From this every 2nd or 3rd field is used to create 24 image samples per second (note that they are not evenly spaced in time which creates part of the “judder” that is most often associated with Cineframe-24). These 24 fields are then line doubled to create 24 “frames”. From there a standard 3:2 sequence is applied for input into the compression engine and to be put on tape. Does it work???? I guess the answer is “sometimes”. There are 4 things that factor into making sure that the Cineframe-24 look is right for what you are doing:
- Because the CCD’s are running at 60i, the longest that the shutter can be open is 1/60th of a second. With most true 24 frame cameras, the shutter is set to be open for 1/48th of a second. This longer shutter opening allows for a natural motion blur to occur which helps to blend motion, which is needed to reduce stuttering with the lower framerate.
- Since the fields used to create the 24 frames are not evenly spaced in time, it lends to a sort of judder in what should be continuous movement.
- The line doubling has a tendency to soften the image
- Because line doubling occurs sometimes from a lower field and sometimes from an upper field, there is a tendency for some artifacts to appear especially in fine horizontal or near horizontal lines.
Adam Wilt also has an in-depth analysis of CineFrame24 HERE.
What about Audio?
Because audio is so important to production, Victory Studios has chosen to offer the HVR-Z1U camcorder for rental, which features professional XLR inputs and separate audio level controls for each channel. Audio for HDV is 2 channels of 16bit/48kHz audio that is compressed MPEG1-Layer 2 to 384kb/s.
Can HDV be transferred to other formats
Victory Studios can transfer 1080i HDV to HDCam, DVCProHD, and D-5HD. We can also downconvert 1080i HDV to DV/DVCam or most other standard definition formats.