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Presents 2005 IMTC Forum

Presents 2005 IMTC Forum. Video Compression after H.264 (Some personal reflections). Presented by Gisle Bjøntegaard Tandberg. Agenda. What has H.264 achieved? General characteristics of hybrid coding What kinds of improvements to expect towards H.265? Where do we go?.

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Presents 2005 IMTC Forum

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  1. Presents 2005 IMTC Forum

  2. Video Compression after H.264(Some personal reflections) Presented by Gisle Bjøntegaard Tandberg

  3. Agenda • What has H.264 achieved? • General characteristics of hybrid coding • What kinds of improvements to expect towards H.265? • Where do we go? IMTC Forum – May 2005 – Eibsee, Germany

  4. What has H.264 achieved? • Relative to H.261 • Considerably increased coding gain • Even higher increase in complexity • H264rd: Rate Distortion optimization • Increased performance • Considerably higher encoder complexity IMTC Forum – May 2005 – Eibsee, Germany

  5. Quality • Bitrate Hybrid coding techniques I • All coding standards based on: • Block motion estimation for prediction • Transform coding of residual signal • This combination is referred to as hybrid coding • This leads to quality/bitrate relation for a picture format: IMTC Forum – May 2005 – Eibsee, Germany

  6. Quality • Bitrate Hybrid coding techniques II • Adding more picture formats • Including picture format as a parameter, coding characteristics is the straight line • The hybrid coder has an optimal point ( ) IMTC Forum – May 2005 – Eibsee, Germany

  7. Hybrid coding techniques III • As a result it is desirable to use ”large” input formats • Which in turn adds to encoder/decoder complexity • Example of suitable bitrates for different formats (30 fps): • QCIF 100 kb/s • CIF 400 kb/s • 4CIF(SD TV) 1500 kb/s •  indicates that the bitrate depends much on the sequence content IMTC Forum – May 2005 – Eibsee, Germany

  8. Improvements: More coding gain I • One goal of H.265 is 2x in coding gain (the same quality at half the bitrate) • This will need hard work and long time • Partly bebause H.264 did a very good job • ”Known” extensions represent (10-20)% improvement • A number of small improvements expected on: • Prediction • Coding of prediction error • Entropy coding IMTC Forum – May 2005 – Eibsee, Germany

  9. More coding gain II • Totally new approaches needed • The problem is that hybrid coding is highly optimized • It is therefore very difficult to find methods that compete • My guess: • It will take (5-8) years (suitable for H.265 in 2012?) • Complexity will increase much (but hardware can cope?) IMTC Forum – May 2005 – Eibsee, Germany

  10. New functionalities I • Improved error resilience was one one of the goals in H.264 • Still this is one of the weak points of H.264 and could be improved • Especially tools to handle packet loss in IP networks are needed • The basic problem is that a compressed signal is more vulnerable to bit loss due to dependies in time and space • Add some redundancy to cope with packet loss • How to do this in the most useful way? • To ensure minimum penalty to picture quality and latency? IMTC Forum – May 2005 – Eibsee, Germany

  11. New functionalities II • Scalability is beeing addressed in JVT • It is still unclear how much and in which way scalability will be used in products and services • Easy ways of stitching several source streams into one display • This is to some extent dealt with in MPEG4, but is not in wide use • A simple solution could be attractive IMTC Forum – May 2005 – Eibsee, Germany

  12. Implementation complexity • Implementation complexity of H.264 is roughly proportional to the bitrate • Going from 384 kb/s to 2Mb/s means 5 times complexity increase • If we also end up with a coding method that is 10 times as complex? • This will be a challenge even for new generations of hardware • H.264 has done a better job on high coding efficiency than keeping complexity low • It is therefore easy to develop simpler versions of H.264 • What if we could maintain H.264 coding efficiency but with much simpler coding/decoding? IMTC Forum – May 2005 – Eibsee, Germany

  13. Activity towards a FAST profile of H.264 • Tandberg brought some 15 documents to ITU/VCEG proposing simplifications to H.264 • At the moment we have (30-35)% reduction in computational requirements (see in the graph) • Technically this profile could be ready within about 1 year – subject to acceptance in ITU (or other fora) IMTC Forum – May 2005 – Eibsee, Germany

  14. Application areas for a FAST profile • Real time communications • Using programable hardware • Coding larger picture formats with existing hardware • Keeping power consumption low • Whenever low complexity matters • A useful starting point for a next generation standard? IMTC Forum – May 2005 – Eibsee, Germany

  15. Where do we go? • Extensions to H.264 in the near future: • JVT will produce a solution for scalability • ”Computational efficiency” extension could be most useful for real time applications • A useful extension could be in the direction of coping with IP packet loss • H.265. 2x compresion • ”Low hanging fruits” are already taken • Therefore: addition of many small improvements • Each increasing coder/decoder complexity • Ready in 2010-2012? IMTC Forum – May 2005 – Eibsee, Germany

  16. Or is H.264 sufficient in the foreseeable future? THANK YOU! IMTC Forum – May 2005 – Eibsee, Germany

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