SRD
SRD ： Spatial Relation Description
SRD is an approach for streaming only spatial sub-parts of a video to display devices, in combination
with the form of adaptive multi-rate streaming that is intrinsically supported by MPEG DASH.
The SRD feature extends the Media Presentation Description (MPD) of MPEG DASH by describing
spatial relationships between associated pieces of video content.
This enables the DASH client to select and retrieve only those video streams at those resolutions that are relevant to the user experience.
SRD Syntax
SRD Syntax
Syntax and semantics of SRD information
source_id
The MPD author can signal SRD descriptors for each of the different content items in the same MPD.
Identical values of source_id in different SRD descriptors indicate that these SRD descriptors belong to the same reference space.
Conversely, SRD descriptors with different source_id have no spatial relationship with each other.
如果source_id相同，说明SRD descriptors属于同一参考空间。
如果source_id不同，说明SRD descriptors没有空间关系。
举例
(1) 例1
<AdaptationSet>
<SupplementalProperty schemeIdUri="urn:mpeg:dash:srd:2014" value="0,3840,2160,3840,2160,7680,2160"/>
...
</AdaptationSet>
(2) 例2
<SupplementalProperty schemeIdUri="urn:mpeg:dash:srd:2014" value="0,2,0,2,2"/>
(3) 例3
<SupplementalProperty schemeIdUri="urn:mpeg:dash:srd:2014" value="0,0,0,1,1,2,2"/>
source_id ： 0
object_x ： 0
object_y : 0
object_width : 1
object_height : 1
total_width : 2
total_height : 2
表明源视频按照2*2进行切割， 当前tile位置为(0, 0), 宽和高的大小均为源视频宽高的2分之一。
MP4Box中如何指定SRD
MP4Box -dash 1000 [other dash params] source.mp4:desc_as=<SupplementalProperty schemeIdUri=\"urn:mpeg:dash:srd:2014\" value=\"0,0,1,1,1,2,2\"/>
indicates that source.mp4 is placed at X=0, Y=1 with width 1 and height 1 on a tiling grid of size 2×2.
References:
https://pdfs.semanticscholar.org/73bb/96a1d8415f675857704ce77739a4fd46f992.pdf
https://gpac.wp.imt.fr/2016/05/25/srdtuto/
