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Slice structure clarification
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Split of Slice() in 3 different parts (Header, Content, Footer).
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@JeromeMartinez @michaelni
JeromeMartinez authored and michaelni committed May 28, 2016
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Expand Up @@ -535,46 +535,17 @@ See [NUT](#references) for more information about elements.
|Slice( i ) { | type |
|    if( version \>= 3 ) | |
|        SliceHeader( i ) | |
|    if( colorspace\_type == 0) { | |
|        for( p = 0; p \< primary\_color\_count; p++ ) { | |
|            Plane( p ) | |
|    } else if( colorspace\_type == 1 ) { | |
|        for( y = 0; y \< height; y++ ) | |
|            for( p = 0; p \< primary\_color\_count; p++ ) { | |
|                Line( p, y ) | |
|    } | |
|    SliceContent( ) | |
|    if ( coder\_type == 0 ) | |
| while ( !byte\_aligned() ) | |
|         padding | u(1) |
|    if( version \>= 3 ) | |
|        slice\_size | u(24) |
|    if( ec ) { | |
|        error\_status | u(8) |
|        slice\_crc\_parity | u(32) |
|    } | |
|        SliceFooter( ) | |
|} | |

**primary\_color\_count** is defined as 1 + ( chroma_planes ? 2 : 0 ) + ( alpha_plane ? 1 : 0 ).

**padding** specifies a bit without any significance and used only for byte alignment.
MUST be 0.

**slice_size** indicates the size of the slice in bytes.
Note: this allows finding the start of slices before previous slices have been fully decoded. And allows this way parallel decoding as well as error resilience.

**error_status** specifies the error status.

| value | error status |
|-------|--------------------------------------|
| 0 | no error |
| 1 | slice contains a correctable error |
| 2 | slice contains a uncorrectable error |
| Other | reserved for future use |

**slice\_crc\_parity** 32 bits that are choosen so that the slice as a whole has a crc remainder of 0.
This is equivalent to storing the crc remainder in the 32-bit parity.
The CRC generator polynom used is the standard IEEE CRC polynom (0x104C11DB7) with initial value 0.

## Slice Header

| | |
Expand Down Expand Up @@ -643,6 +614,53 @@ Inferred to be 0 if not present.
| 1 | raw PCM |
| Other | reserved for future use |

## Slice Content

| |
|------------------------------------------------------------|:------|
|SliceContent( ) { | type |
|    if( colorspace\_type == 0) { | |
|        for( p = 0; p \< primary\_color\_count; p++ ) { | |
|            Plane( p ) | |
|    } else if( colorspace\_type == 1 ) { | |
|        for( y = 0; y \< height; y++ ) | |
|            for( p = 0; p \< primary\_color\_count; p++ ) { | |
|                Line( p, y ) | |
|    } | |
|} | |

**primary\_color\_count** is defined as 1 + ( chroma_planes ? 2 : 0 ) + ( alpha_plane ? 1 : 0 ).

## Slice Footer

Note: slice footer is always byte aligned.

| |
|------------------------------------------------------------|:------|
|SliceFooter( ) { | type |
|    slice\_size | u(24) |
|    if( ec ) { | |
|        error\_status | u(8) |
|        slice\_crc\_parity | u(32) |
|    } | |
|} | |

**slice_size** indicates the size of the slice in bytes.
Note: this allows finding the start of slices before previous slices have been fully decoded. And allows this way parallel decoding as well as error resilience.

**error_status** specifies the error status.

| value | error status |
|-------|--------------------------------------|
| 0 | no error |
| 1 | slice contains a correctable error |
| 2 | slice contains a uncorrectable error |
| Other | reserved for future use |

**slice\_crc\_parity** 32 bits that are choosen so that the slice as a whole has a crc remainder of 0.
This is equivalent to storing the crc remainder in the 32-bit parity.
The CRC generator polynom used is the standard IEEE CRC polynom (0x104C11DB7) with initial value 0.

## Parameters

| | |
Expand Down Expand Up @@ -870,24 +888,27 @@ For each Frame with keyframe value of 0, each slice MUST have the same value of
### Multi-threading support and independence of slices
The bitstream is parsable in two ways: in sequential order as described in this document or with the pre-analysis of slice\_size fields. slice\_size fields pre-analysis allows multi-threading as well as independence of slice content (a bitstream error in a slice content has no impact on the decoding of the other slices).
The bitstream is parsable in two ways: in sequential order as described in this document or with the pre-analysis of the footer of each slice. Each slice footer contains a slice\_size field so the boundary of each slice is computable without having to parse the slice content. That allows multi-threading as well as independence of slice content (a bitstream error in a slice header or slice content has no impact on the decoding of the other slices).
After having checked keyframe field, a decoder SHOULD parse slice_size fields, from slice\_size of the last slice at the end of the frame up to slice\_size of the first slice at the beginning of the frame, before parsing slices, in order to have slices boundaries. A decoder MAY fallback on sequential order e.g. in case of corrupted frame (frame size unknown, slice\_size of slices not coherant...) or if there is no possibility of seek into the stream.
Architecture overwiew of slices in a frame:
-
| |
|:--------------------------------------------------------------|
| first slice header |
| first slice content |
| first slice slice\_size + error\_status + slice\_crc\_parity |
| first slice footer |
|---------------------------------------------------------------|
| second slice header |
| second slice content |
| second slice slice\_size + error\_status + slice\_crc\_parity |
| second slice footer |
|---------------------------------------------------------------|
| ... |
|---------------------------------------------------------------|
| last slice header |
| last slice content |
| last slice slice\_size + error\_status + slice\_crc\_parity |
| last slice footer |
# Changelog
Expand Down

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