Description:As attached , Claims:1. A video encoder (2610) configured to
encode a plurality of pictures of a video into a data stream (2065), wherein each of the plurality of pictures is split into a predetermined number of subpictures, each subpicture comprising boundaries for boundary extension for motion compensation,
wherein the video encoder (2610) is configured to encode each of the subpictures using context-adaptive binary arithmetic coding,
wherein the video encoder is configured to provide the data stream for at least one subpicture at the end of one or more slices (2631, 2632, 2633) of each subpicture with zero-words so as to avoid that any of the subpictures exceeds a predetermined bin-to- bit ratio.

2. The video encoder as claimed in claim 1, further configured to
evaluate each subpicture for an independence property, e.g. subpic_treated_as_pic_flag, and for corresponding level conformance indication, e.g. in a supplemental enhancement information, SEI, message, and
provide the zero-words for a subpicture only in response to and in accordance with the evaluation.

3. The video encoder (2610) as claimed in claim 1 or 2, configured to provide the data stream at the end of one or more slices of each subpicture of the at least one subpicture with the zero-words such that the number of bins coded for the respective subpicture into the data stream using the context adaptive arithmetic coding is less than or equal to a number determined using a product between a predetermined factor and a byte length of one or more VCL NAL units of the data stream associated with the respective subpicture.

4. The video encoder (2610) as claimed in claim 1 or 2, configured to provide the data stream at the end of one or more slices of each subpicture of the at least one subpicture with the zero-words such that the number of bins coded for the respective subpicture into the data stream using the context adaptive arithmetic coding is less than or equal to a number determined using a sum of a first product between a first predetermined factor and a byte length of one or more VCL NAL units of the data stream associated with the respective subpicture and a second product between a second predetermined factor, a minimum number of bits per coding block and a number of coding blocks the respective subpicture is composed of.

5. A method for encoding a video, comprising
encoding a plurality of pictures of a video into a data stream, wherein each of the plurality of pictures is split into a predetermined number of subpictures, each subpicture comprising boundaries for boundary extension for motion compensation,
wherein the method comprises encoding each of the subpictures using context- adaptive binary arithmetic coding,
wherein the method comprises providing the data stream (2605) for at least one subpicture at the end of one or more slices (2631, 2632, 2633) of each subpicture with zero-words so as to avoid that any of the subpictures exceeds a predetermined bin-to- bit ratio.

6. The method for encoding a video as claimed in claim 5, further comprising
evaluating each subpicture for an independence property, e.g. subpic_treated_as_pic_flag, and for corresponding level conformance indication, e.g. in a supplemental enhancement information, SEI, message, and
providing the zero-words for a subpicture only in response to and in accordance with the evaluation.

7. The method for encoding a video as claimed in claim 5 or 6, comprising providing the data stream at the end of one or more slices of each subpicture of the at least one subpicture with the zero-words such that the number of bins coded for the respective subpicture into the data stream using the context adaptive arithmetic coding is less than or equal to a number determined using a product between a predetermined factor and a byte length of one or more VCL NAL units of the data stream associated with the respective subpicture.

8. The method for encoding a video as claimed in claim 5 or 6 or 7, comprising providing the data stream at the end of one or more slices of each subpicture of the at least one subpicture with the zero-words such that the number of bins coded for the respective subpicture into the data stream using the context adaptive arithmetic coding is less than or equal to a number determined using a sum of a first product between a first predetermined factor and a byte length of one or more VCL NAL units of the data stream associated with the respective subpicture and a second product between a second predetermined factor, a minimum number of bits per coding block and a number of coding blocks the respective subpicture is composed of.

9. A video decoder (2640) configured to
decode a plurality of pictures of a video from a data stream (2065), wherein each of the plurality of pictures is split into a predetermined number of subpictures, each subpicture comprising boundaries for boundary extension for motion compensation,
wherein the video decoder (2640) is configured to decode each of the subpictures using context-adaptive binary arithmetic decoding,
wherein the video decoder is configured to decode for at least one subpicture at the end of one or more slices (2631, 2632, 2633) of each subpicture a number of zero- words so that a bin-to-bit ratio is below a predetermined bin-to-bit ratio.

10. The video decoder (2640) as claimed in claim 9, configured to
determine the number of zero-words by continuing reading zero-words until the bin-to- bit ratio is below the predetermined bin-to-bit ratio, or by discriminating zero-words from other syntax elements syntactically.
11. The video decoder as claimed in claim 9 or 10, further configured to
evaluate each subpicture for an independence property, e.g. subpic_treated_as_pic_flag, and for corresponding level conformance indication, e.g. in a supplemental enhancement information, SEI, message, and
decode the zero-words for a subpicture only in response to and in accordance with the evaluation.

12. The video decoder (2640) as claimed in claim 9, 10, or 11, configured to
decode the data stream at the end of one or more slices of each subpicture of the at least one subpicture with the zero-words such that the number of bins coded for the respective subpicture into the data stream using the context adaptive arithmetic coding is less than or equal to a number determined using a product between a predetermined factor and a byte length of one or more VCL NAL units of the data stream associated with the respective subpicture.

13. The video decoder (2640) as claimed in claim 9, 10, or 11, configured to
decode the data stream at the end of one or more slices of each subpicture of the at least one subpicture with the zero-words such that the number of bins coded for the respective subpicture into the data stream using the context adaptive arithmetic coding is less than or equal to a number determined using a sum of a first product between a first predetermined factor and a byte length of one or more VCL NAL units of the data stream associated with the respective subpicture and a second product between a second predetermined factor, a minimum number of bits per coding block and a number of coding blocks the respective subpicture is composed of.