EBU Codec testing at the Institut für Rundfunktechnik
Recently, staff from BBC R&D's Broadcast and Connected Systems section and the BBC's Head of Technology for HD and Ultra HD were in Munich at the Institut für Rundfunktechnik (IRT). They were there to take part in the European Broadcasting Union's (EBU's) next generation studio codec tests.
In order to successfully deploy Ultra High Definition Television (Ultra HD/UHDTV), the BBC needs to evaluate the suitability of commercially available codecs for acquisition and editing of UHDTV content. The codecs under test from 2 major broadcast equipment manufacturers provided both intra-frame and long-GoP implementations of H.264/AVC for studio quality compression of 720p50, 1080i25, 1080p50 and UHD material. All implementations are also designed to be suitable for editing on non-linear systems.
The first round of testing was to evaluate the codecs for 720p50, 1080i25 and 1080p50 use. Planning is underway for further tests which will include testing of higher frame rates and higher dynamic ranges as these are new challenges for the codec manufacturers.
By participating in this set of tests undertaken by public service broadcasters from across Europe, we can agree common formats facilitating programme exchange between EBU members and the wider industry. Additionally, the BBC saves money as we do not have to replicate the tests thus saving on engineering resources.
The tests were undertaken by staff from the BBC, German public broadcast research institute IRT, Swedish broadcaster Sveriges Television (SVT), Norwegian broadcaster Norsk Rikskringkasting (NRK), Belgian broadcaster Vlaamse Radio- en Televisieomroeporganisatie (VRT), Italian broadcaster Radiotelevisione Italiana (RAI) and staff from the EBU Technical Department. Results will be available to EBU members shortly.
Why another acquisition codec?
Firstly, these codecs are designed to outperform the current offerings and, secondly, these codecs can be seen as a stepping stone towards Ultra HD codecs. Finally, these codecs are compliant with an open standard and should be able to be used with any decoder that implements the correct profile.
Many current acquisition codecs use a profile of MPEG-2 Part 2 and therefore, as currently specified, have a maximum frame size of 1920x1088, a maximum frame rate of 60 Hz and are limited to 8 bits/sample.
All the codecs supplied for test by the 2 major broadcast equipment manufacturers are based on the newer H.264/AVC standard which can be extended to Ultra HD frame sizes. However, as Andrew Cotton mentioned in a recent blog post, Ultra HD is more than just the oft-publicised “4k” resolution. The codecs used for Ultra HD production will need to handle high frame rates, larger colour spaces, higher bit depths and a higher dynamic range than we are currently used to.
Further work will be required as broadcast manufacturers bring more open and proprietary Ultra HD-compatible codecs to market (e.g. Apple ProRes and SMPTE VC-3 (DNxHD)). Additional work will be required to ensure that Digital Cinema formats such as OpenEXR and DCP can be successfully imported into a broadcast environment.
Further testing will be undertaken early next year into the codecs' Ultra HD performance.