Inter and Intra prediction across slice

micromad · 10th November 2008, 19:12

It is stated in all the documents that inter and intra prediction are not allowed across the slice. However, it seems not true from my experiments...
I encoded the video sequence as "one row of MB as a slice", then corrupted one slice only through packet loss. After the decoding, I've seem some deterioration expanding over the slice in the following frames.

Can anybody explain to me what causes this effect? Its the nature of inter prediction or Skip mode or something else?

I've attached a screenshot. you can see the effect clearly on the right edge.

Thanks!

akupenguin · 10th November 2008, 21:43

Forbidding of inter prediction across slices refers to the mvs themselves, which would normally be predicted from neighboring blocks in the same frame, but not if those blocks are in another slice. The pixels that the mvs point to can still be anywhere in the previous frames.

micromad · 11th November 2008, 12:48

Thank you so much for answering!

micromad · 13th November 2008, 16:31

Following this topic: may i say the "scattering" of the errors from previous frames is decided by the MVs and search range? is there any other parameter related?
Thanks!

akupenguin · 13th November 2008, 19:59

The scattering is determined entirely by MVs. And the MVs are determined mostly by what motion is present in the video content. The scattering visible in your screenshot is small enough that I expect it not to have been limited by search range.

10th November 2008, 19:12	#1 \| Link
micromad Registered User Join Date: Feb 2008 Posts: 3	Inter and Intra prediction across slice It is stated in all the documents that inter and intra prediction are not allowed across the slice. However, it seems not true from my experiments... I encoded the video sequence as "one row of MB as a slice", then corrupted one slice only through packet loss. After the decoding, I've seem some deterioration expanding over the slice in the following frames. Can anybody explain to me what causes this effect? Its the nature of inter prediction or Skip mode or something else? I've attached a screenshot. you can see the effect clearly on the right edge. Thanks! Attached Images

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10th November 2008, 21:43	#2 \| Link
akupenguin x264 developer Join Date: Sep 2004 Posts: 2,392	Forbidding of inter prediction across slices refers to the mvs themselves, which would normally be predicted from neighboring blocks in the same frame, but not if those blocks are in another slice. The pixels that the mvs point to can still be anywhere in the previous frames.

11th November 2008, 12:48	#3 \| Link
micromad Registered User Join Date: Feb 2008 Posts: 3	Thank you so much for answering!

13th November 2008, 16:31	#4 \| Link
micromad Registered User Join Date: Feb 2008 Posts: 3	Following this topic: may i say the "scattering" of the errors from previous frames is decided by the MVs and search range? is there any other parameter related? Thanks!

13th November 2008, 19:59	#5 \| Link
akupenguin x264 developer Join Date: Sep 2004 Posts: 2,392	The scattering is determined entirely by MVs. And the MVs are determined mostly by what motion is present in the video content. The scattering visible in your screenshot is small enough that I expect it not to have been limited by search range.