Sub-bitstream extraction

1. A sub-bitstream extraction method applicable to a bitstream of multiple access units comprising a respective encoded picture of a video sequence, said method comprising:

identifying an access unit among said bitstream comprising said multiple access units; and

discarding said access unit and all access units in said bitstream that can depend on said access unit to form a sub-bitstream having no access unit that can depend on said access unit,

wherein each picture of said video sequence has a respective layer identifier identifying a respective layer, discarding said access unit comprises discarding said access unit and all access units in said bitstream having layer identifier higher than or equal to said layer identifier of said access unit and following said access unit according to a decoding order of said bitstream but preceding, according to a defined order of said bitstream, any next layer switching point having a layer identifier lower than or equal to said layer identifier of said access unit.

2. The method according to claim 1 , wherein discarding said access unit comprises:

discarding said access unit from said bitstream; and

discarding all access units in said bitstream having layer identifier higher than or equal to said layer identifier of said access unit and following said access unit according to said decoding order but preceding, according to said defined order, a next layer switching point having a layer identifier lower than or equal to said layer identifier of said access unit if said bitstream comprises a next layer switching point having a layer identifier lower than or equal to said layer identifier of said access unit and following said access unit according to said defined order; or

discarding all access units in said bitstream having layer identifier higher than or equal to said layer identifier of said access unit and following said access unit according to said decoding order if said bitstream does not comprise any next layer switching point having a layer identifier lower than or equal to said layer identifier of said access unit and following said access unit according to said defined order.

3. The method according to claim 1 , wherein discarding said access unit comprises discarding said access unit and all access units in said bitstream having layer identifier higher than or equal to said layer identifier of said access unit and following said access unit according to a decoding order of said bitstream but preceding, according to said decoding order of said bitstream, any next layer switching point having a layer identifier lower than or equal to said layer identifier of said access unit.

4. The method according to claim 1 , wherein discarding said access unit comprises discarding said access unit and all access units in said bitstream having layer identifier higher than or equal to said layer identifier of said access unit and following said access unit according to a decoding order of said bitstream but preceding, according to an output order of said bitstream, any next layer switching point having a layer identifier lower than or equal to said layer identifier of said access unit.

5. The method according to claim 1 , wherein:

each picture of said video sequence has a respective temporal identifier identifying a respective temporal layer, and

said layer switching point is a temporal layer switching point selected from a group consisting of a temporal layer access, TLA, picture and an instantaneous decoding refresh, IDR, picture.

6. The method according to claim 1 , wherein discarding said access unit comprises:

marking said access unit as to be removed from said bitstream;

marking said all access units in said bitstream that can depend on said access unit as to be removed from said bitstream; and

discarding all access units of said bitstream marked as to be removed from said bitstream.

7. The method according to claim 1 , wherein discarding said access unit and said all access units is performed without decoding said access unit.

8. A sub-bitstream extracting device comprising:

an access unit identifier configured to identify an access unit among a bitstream of multiple access units comprising a respective encoded picture of a video sequence; and

an access unit discarder configured to discard said access unit and all access units in said bitstream that can depend on said access unit to form a sub-bitstream having no access unit that can depend on said access unit,

wherein each picture of said video sequence has a respective layer identifier identifying a respective layer, said access unit discarder is configured to discard said access unit and all access units in said bitstream having layer identifier higher than or equal to said layer identifier of said access unit and following said access unit according to a decoding order of said bitstream but preceding, according to a defined order of said bitstream, any next layer switching point having a layer identifier lower than or equal to said layer identifier of said access unit.

9. The device according to claim 8 , wherein said access unit discarder is configured to i) discard said access unit from said bitstream, and iia) discard all access units in said bitstream having layer identifier higher, than or equal to said layer identifier of said access unit and following said access unit according to said decoding order but preceding, according to said defined order, a next layer switching point having a layer identifier lower than or equal to said layer identifier of said access unit if said bitstream comprises a next layer switching point having a layer identifier lower than or equal to said layer identifier of said access unit and following said access unit according to said defined order, or iib) discard all access units in said bitstream having layer identifier higher than or equal to said layer identifier of said access unit and following said access unit according to said decoding order if said bitstream does not comprise any next layer switching point having a layer identifier lower than or equal to said layer identifier of said access unit and following said access unit according to said defined order.

10. The device according to claim 8 , wherein said access unit discarder is configured to discard said access unit and all access units in said bitstream having layer identifier higher than or equal to said layer identifier of said access unit and following said access unit according to a decoding order of said bitstream but preceding, according to said decoding order of said bitstream, any next layer switching point having a layer identifier lower than or equal to said layer identifier of said access unit.

11. The device according to claim 8 , wherein said access unit discarder is configured to discard said access unit and all access units in said bitstream having layer identifier higher than or equal to said layer identifier of said access unit and following said access unit according to a decoding order of said bitstream but preceding, according to an output order of said bitstream, any next layer switching point having a layer identifier lower than or equal to said layer identifier of said access unit.

12. The device according to claim 8 , further comprising:

a marking unit configured to i) mark said access unit as to be removed from said bitstream, and ii) mark said all access units in said bitstream that can depend on said access unit as to be removed from said bitstream, wherein

said access unit discarder is configured to discard all access units of said bitstream marked as to be removed from said bitstream.

13. The device according to claim 8 , wherein said access unit discarder is configured to discard said access unit and said all access units without decoding said access unit.

14. A decoder comprising a sub-bitstream extracting device according to claim 8 .

15. A mobile device comprising a decoder according to claim 14 .

16. An encoder comprising a sub-bitstream extracting device according to claim 8 .

17. A mobile device comprising an encoder according to claim 16 .