Uncompressed video, also called Clean HDMI, is digital video information that has not been compressed, or was not processed with compression on it when the video was captured directly via video capture (e.g. from a digital camera). It refers to the related data stream or the file format used in the video capture process. The purpose is to provide significantly higher quality video compared to lossy compression, allowing even resolution upscaling.
Although HD video capable cameras often include an HDMI interface for playback or live preview, most cameras compress the signal substantially, using a lossy compression method such as MPEG or H.264. In the compression process, a substantial amount of the captured data is removed, which reduces visual quality. Editing video which has never been compressed allows a final result with better quality, and compression is then applied after all editing has been performed. In a true "Clean HDMI" implementation, the camera will either transmit the signal as it is captured "live," without the intermediate use of lossy compression, or the camera will capture, store, and transmit video in a RAW uncompressed format.
This article focuses on HDMI, because it is the dominant digital video interface used in cameras today. However, uncompressed video can be transmitted over other types of baseband video interfaces, such as DVI, DisplayPort and SDI. Uncompressed video can also be copied from a storage card, if the video is captured in a RAW format. It is important to note that all video modes used in the HDMI transmit uncompressed digital video. The distinction here is that the video content is "clean," and has never been subjected to quality loss from compression.
Currently uncompressed video is supported by Nikon DSLRs with the Expeed 3 (FR) and Expeed 4 image/video processor (currently Nikon D4, D4S, D800/D800E, D810, D600, D610, D7100, D5200 and D5300), the Canon EOS-1D C, the Canon 5D Mark III with firmware 1.2.1, the Sony A6000 and professional video cameras (see list of video cameras supporting a raw format), which use proprietary raw video formats like CinemaDNG (open format) or ArriRaw with similarities to the raw image format.
Characteristics
Due to the high video compression in MPEG encoding, the video quality of uncompressed video delivers even more image resolution, color quality, motion information, and sharpness than the related Raw image format.
It has the further advantage of higher quality due to no motion blur (no motion compensation) and no compression artifacts.
Currently there is no standardized uncompressed video file format except for HDMI, which uses the YCbCr and RGB formats listed below. This makes it necessary to store it best with a related description file about the used resolution and video mode. These files can be combined with lossless compression with the use of file archivers.
Lossless video compression
Lossless video compression can be delivered with a variety of video codecs. In test some codecs performed an average compression of over factor 3.
Uncompressed video recording
Setting up the camera is often new especially for DSLR users. The built in video interface in cameras is mostly an HDMI or, in professional cameras, a Serial digital interface (SDI or HD-SDI); converters between both are available.
Uncompressed video recorder
Portable recorders are an easy, reliable and complete solution for receiving and storing uncompressed video. Partly they receive uncompressed video, but only record lossy compressed video, often in the lossy Apple ProRes 422 or DNxHD codecs. Professional recorders support multiple channels of uncompressed HDMI, DVI or (HD-)SDI recording, but are limited by the total data rate.
Recording to a computer
Recording to a computer enables low-cost to highest performance solutions for laptop or desktop computers, but the computer should be prepared as it must act like a real-time operating system (RTOS). Any other significant program activity including background processes - for example not needed Windows startup processes (use for example Autoruns) or Windows services (use Service Control Manager), including automatic updates or virus scanners - may disrupt, distort or stop the video recording. Disconnection of not needed computer networks and increasing the process priority of the recording realtime process often helps to use most of the computer speed. Hard disk drives have to be fast solid-state drives (SSDs) and/or RAID to be capable of the data-rate of HD videos and/or multiple channels.
Video capture interface
HDMI, DVI and HD-SDI inputs are available as PCI Express (partly multi-channel) or ExpressCard, USB 3.0 and Thunderbolt interface also for 2160p (4K resolution).
Wireless video interface
Most Wireless interfaces like Wireless LAN (WLAN, Wi-Fi), WiDi, Wireless Home Digital Interface (WHDI), can be used to transmit uncompressed digital video, but only with low resolutions, as even 1920x1080p@24 Hz requires 1.2 Gbit/s data rate exceeding for example IEEE 802.11ac. The WirelessHD interface, however, which uses a 60 GHz wireless link, can transmit uncompressed digital video. The Wireless Gigabit Alliance also aims to use a 60 GHz wireless link. However, any disruption or bandwidth decrease of the wireless connection will reduce quality, or even stop the video recording.
Uncompressed video recording software
Software for uncompressed video is often supplied with suitable hardware or available for free: Ingex (open source).
Storage and Data Rates for Uncompressed Video
Constant bitrate formula: Uncompressed data rate = color depths * vertical resolution * horizontal resolution * refresh frequency
- Examples
24bit @ 1080i @ 60fps :24*1920*1080*60/2=1.49 Gbps.
24bit @ 1080p @ 60fps :24*1920*1080*60=2.98 Gbit/s.
The storage and data rates for the widely used YCbCr 4:2:2 chroma subsampling uncompressed video are listed below:
- 525 NTSC uncompressed
8 bit @ 720 x 486 @ 29.97fps = 20 MB per/sec, or 70 GB/hr.
10 bit @ 720 x 486 @ 29.97fps = 27 MB/s, or 94 GB/hr.
- 625 PAL uncompressed
8 bit @ 720 x 576 @ 25fps = 20 MB/s, or 70 GB/hr.
10 bit @ 720 x 576 @ 25fps = 26 MB/s, or 93 GB/hr.
- 720p HDTV uncompressed
8 bit @ 1280 x 720 @ 59.94fps = 105 MB/s, or 370 GB/hr.
10 bit @ 1280 x 720 @ 59.94fps = 140 MB/s, or 494 GB/hr.
- 1080i and 1080p HDTV uncompressed
8 bit @ 1920 x 1080 @ 24fps = 95 MB/s, or 334 GB/hr.
10 bit @ 1920 x 1080 @ 24fps = 127 MB/s, or 445 GB/hr.
8 bit @ 1920 x 1080 @ 25fps = 99 MB/s, or 348 GB/hr.
10 bit @ 1920 x 1080 @ 25fps = 132 MB/s, or 463 GB/hr.
8 bit @ 1920 x 1080 @ 29.97fps = 119 MB/s, or 417 GB/hr.
10 bit @ 1920 x 1080 @ 29.97fps = 158 MB/s, or 556 GB/hr.
1080i and 1080p HDTV RGB (4:4:4) uncompressed
10 bit @ 1280 x 720p @ 60fps = 211 MB/s, or 742 GB/hr.
10 bit @ 1920 x 1080 @ 24fps = 190 MB/s, or 667 GB/hr.
10 bit @ 1920 x 1080 @ 50i = 198 MB/s, or 695 GB/hr.
10 bit @ 1920 x 1080 @ 60i = 237 MB/s, or 834 GB/hr.
HDMI Specifications
According to HDMI 1.3a Spec.
Detailed timing is found in CEA-861-D or a later version of CEA-861 for the following video format timings. HDMI 2.0 supports higher resolutions, which are defined in CEA-861-F.
Cameras mostly use the progressive segmented frame format: for example a 25p/30p progressive scan is transported in a 50i/60i interlaced format respectively, but with identical information: No deinterlacing should be used.
- Primary Video Format Timings
• 640x480p @ 59.94/60 Hz
• 1280x720p @ 59.94/60 Hz
• 1920x1080i @ 59.94/60 Hz
• 720x480p @ 59.94/60 Hz
• 720(1440)x480i @ 59.94/60 Hz
• 1280x720p @ 50 Hz
• 1920x1080i @ 50 Hz
• 720x576p @ 50 Hz
• 720(1440)x576i @ 50 Hz
- Secondary Video Format Timings
• 720(1440)x240p @ 59.94/60 Hz
• 2880x480i @ 59.94/60 Hz
• 2880x240p @ 59.94/60 Hz
• 1440x480p @ 59.94/60 Hz
• 1920x1080p @ 59.94/60 Hz
• 720(1440)x288p @ 50 Hz
• 2880x576i @ 50 Hz
• 2880x288p @ 50 Hz
• 1440x576p @ 50 Hz
• 1920x1080p @ 50 Hz
• 1920x1080p @ 23.98/24 Hz
• 1920x1080p @ 25 Hz
• 1920x1080p @ 29.97/30 Hz
• 2880x480p @ 59.94/60 Hz
• 2880x576p @ 50 Hz
• 1920x1080i (1250 total) @ 50 Hz
• 720(1440)x480i @ 119.88/120 Hz
• 720x480p @ 119.88/120 Hz
• 1920x1080i @ 119.88/120 Hz
• 1280x720p @ 119.88/120 Hz
• 720(1440)x480i @ 239.76/240 Hz
• 720x480p @ 239.76/240 Hz
• 720(1440)x576i @ 100 Hz
• 720x576p @ 100 Hz
• 1920x1080i @ 100 Hz
• 1280x720p @ 100 Hz
• 720(1440)x576i @ 200 Hz
• 720X576p @ 200 Hz
- Pixel Encodings and Color Depth
There are three different pixel encodings that may be sent across an HDMI cable: YCbCr 4:4:4 (chroma subsampling), YCbCr 4:2:2 and RGB 4:4:4.
There are four color depths supported: 24-, 30-, 36- and 48-bits per pixel. In HDMI 2.0, it is possible to transmit 4:2:0 chroma subsampling, but only in 4K50 and 4K60 resolution.
See also
- List of video cameras supporting a raw format
- Data compression
- Nikon Expeed Video processor
- Uncompressed audio
- DPX and MXF files are used in professional video files systems.
- TIFF files are used in AV and professional video files systems.
References
External links
- Video bitrate calculator Forret
- Uncompressed Digital Video Creative Planet Network
- Uncompressed vs. Compressed Video Creative Planet Network
- Master Guide to Rigging a Nikon D800 or D800E for Video Wolfcrow