Digital Recording of Performing Arts: Formats and Conversion
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detailed approach also when the transfer of rights forms part of an employment contract between the producer of Digital recording of performing the recording and the live crew. arts: formats and conversion • Since the area of activity most probably qualifies as Stijn Notebaert, Jan De Cock, Sam Coppens, Erik Mannens, part of the ‘cultural sector’, separate remuneration for Rik Van de Walle (IBBT-MMLab-UGent) each method of exploitation should be stipulated in the Marc Jacobs, Joeri Barbarien, Peter Schelkens (IBBT-ETRO-VUB) contract. If no separate remuneration system has been set up, right holders might at any time invoke the legal default mechanism. This default mechanism grants a proportionate part of the gross revenue linked to a specific method of exploitation to the right holders. The producer In today’s digital era, the cultural sector is confronted with a may also be obliged to provide an annual overview of the growing demand for making digital recordings – audio, video and gross revenue per way of exploitation. This clause is crucial still images – of stage performances available over a multitude of in order to avoid unforeseen financial and administrative channels, including digital television and the internet. Essentially, burdens in a later phase. this can be accomplished in two different ways. A single entity can act as a content aggregator, collecting digital recordings from • Determine geographical scope and, if necessary, the several cultural partners and making this content available to duration of the transfer for each way of exploitation. content distributors or each individual partner can distribute its own • Include future methods of exploitation in the contract. recordings via the internet. Both methods (content aggregation and Although the legitimacy of this kind of clause is not individual internet distribution) imply a different set of requirements completely guaranteed, we believe future or unknown for audio-visual compression and container formats. ways of exploitation can be covered. In order to guarantee Content aggregation requires high-resolution, high-quality the applicability of such a clause, make sure two material, suitable for editing/post-processing and conversion additional conditions are fulfilled: (1) if the transfer of to different audio-visual formats tailored to specific distribution future/unknown means of exploitation is done within the channels. Compression and container formats must be chosen framework of an employment contract, part of the profit so that the content can be processed using (semi)professional generated through that specific method of future/unknown production tools. This means that interoperability is essential, exploitation should be granted to the right holder and; (2) which implies the use of internationally standardized solutions. insert a clause which secures the validity of the rest of the Since the material is typically transferred offline, storage and contract in case one clause turns out to be invalid. bandwidth limitations are of secondary importance. However, constantly increasing quality and resolution demands and the need for an efficient production chain prohibit the use of older, sub-optimal compression techniques. 94 table of contents 95 For internet distribution, the formats must be flexible enough to coMPrEssIon Formats support a wide range of terminals (PC, personal media player, smartphone, etc.) and bandwidth-limited connections (xDSL, still image compression UMTS, etc.). This specifically implies the use of compression algorithms with a very good rate-distortion performance, (i.e. As mentioned in the introduction, there is a difference in the algorithms which require a minimal number of bits to obtain a requirements for the two scenarios, content aggregation and given, suitable quality) over a large range of resolutions, frame distribution via the internet. The first scenario puts the emphasis rates, and quality levels. Additionally, it is of prime importance on quality, implying the use of lossless image compression, that the distribution formats are supported by popular playback whereas the second scenario must take into account the limitations software. imposed by the internet connection bandwidth, implying the use Establishing a standard set of suitable content aggregation and of lossy image compression. For the first scenario, the following distribution formats necessitates efficient tools for the conversion standardized image coding techniques, operated in lossless of contributed and legacy content to the chosen formats. This mode, were tested: JPEG-LS, JPEG 2000, JPEG XR (HD Photo) conversion is often a time- and resource-consuming process. and PNG. The evaluation of the compression performance of The efficiency of conversion tools can be improved by performing these codecs is straightforward. The most efficient codec is the transcoding instead of re-encoding. Transcoding implies the one that offers the highest compression ratio, i.e. the size of use of information present in the compressed representation of the uncompressed image divided by the size of the compressed the original material to facilitate low-complexity conversion to a image, for a set of representative test images. In our evaluation, different format. the employed test material consisted of a set of high resolution In the project, the problems of compression and container images related to performing arts productions and exhibiting format selection and that of efficient format conversion through varying characteristics. The results of our experiments clearly transcoding have been investigated in great detail. In this chapter, show that PNG has the worst compression efficiency. JPEG XR the main conclusions of this work will be presented. A selection performs significantly better than PNG but its efficiency is still of compression formats for video, audio and still images will considerably worse than that of JPEG-LS and JPEG 2000. For be discussed. The next section will elaborate on the choice of a black and white images, the performance of JPEG-LS and JPEG proper container format. Finally, the work on transcoding will be 2000 is very similar but for colour images, JPEG-LS outperforms summarized. JPEG 2000. From the viewpoint of professional support, none of the compared compression formats should pose a problem for professional image processing and desktop publishing software. This leads us to conclude that JPEG-LS is the best choice for image compression in the content aggregation scenario. 96 table of contents 97 Figure 1: Compression ratios for lossless still image Microsoft is actively pushing support for JPEG XR, as shown compression (scenario 1) by the fact that JPEG XR is natively supported in all versions of Windows Vista. As a conclusion, based on its performance and end-user support, JPEG XR is our recommended choice for the 10 JPEG 2000 internet distribution scenario. Figure 2 presents a typical PSNR JPEG-LS graph – showing PSNR values in function of corresponding bit 8 JPEG XR PNG rates – from our tests with lossy image compression. 6 Figure 2: Typical PSNR graph for lossy image compression 4 (scenario 2) 2 40 JPEG 2000 0 JPEG XR IMG IMG IMG IMG IMG IMG IMG IMG IMG IMG IMG IMG IMG IMG IMG IMG IMG IMG IMG Compression ratio (higher is better) JPEG 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 35 ] dB [ 30 For the second scenario, distribution via the internet, the following standardized lossy image coding techniques were tested: JPEG, PSNR JPEG 2000 and JPEG XR (HDPhoto). The images used were the 25 same as for the first scenario but their resolution was uniformly reduced to obtain pictures with a maximum height of 768 pixels 20 (typical height of a modern computer monitor). The test images 0 1 2 3 were coded using different bit rates (ranging from 0.1875 to 3 bits Bitrate [bpp] per pixel). In each case, the quality of the decoded video material was measured using the peak signal-to-noise ratio (PSNR), which expresses the quality difference between the original and the Audio compression compressed material. The test results for the second scenario clearly show that classical JPEG coding is no match for the other For the content aggregation scenario the following audio com- two image coding techniques. The results for JPEG 2000 and JPEG pression techniques were evaluated: MPEG-4 Audio Lossless XR show that JPEG 2000 slightly outperforms JPEG XR. However, Coding (ALS), Free Lossless Audio Codec (FLAC), Monkey’s Audio the performance difference is limited. Based on its performance, (APE), Windows Media Audio (WMA) Lossless 9.2 and WAVPACK. JPEG 2000 is the winner, closely followed by JPEG XR. However, Lossless audio compression techniques were selected, since the end-user support for JPEG 2000 is rather limited, whereas they offer sufficient size reduction to be practically useful 98 table of contents 99 in professional environments, while introducing no quality Figure 3: Compression ratios for lossless audio compression degradation. Apart from MPEG-4 ALS, these compression (scenario 1) techniques are not officially standardized and WMA Lossless is even a closed-source audio compression technique. To evaluate 2.0 the performance of the selected codecs, their compression ratio was compared on different representative audio fragments with 1.5 varying characteristics. All fragments had two channels (stereo) and a sampling rate of 96 KHz with 24 bits per sample. 1.0 The experimental results, graphically presented in Figure 3, show that MPEG-4 ALS yields the best compression performance, 0.5 closely followed by Monkey’s Audio. The third place is shared by FLAC and WMA Lossless. WAVPACK shows the worst performance. Compressiefactor (hoger is beter) 0.0 Based on compression performance alone, MPEG-4 ALS is AUD AUD AUD AUD AUD AUD AUD AUD AUD AUD AUD AUD AUD AUD AUD AUD AUD AUD AUD AUD clearly the winner. However, the current generation of media 1 2A 2B 2C 2D 2E 3A 3B 3C 4A 4B 5A 5B 5C 6 7A 7B 8A 8B 9 applications seems to have only limited support for lossless audio FLAC compression in general and for MPEG-4 ALS and Monkey’s Audio APE APE specifically.