[Cin] DAR, PAR and SAR, again

Terje J. Hanssen terjejhanssen at gmail.com
Tue Jan 23 21:33:34 CET 2024

Den 23.01.2024 21:13, skrev Terje J. Hanssen:
> Den 23.01.2024 18:35, skrev Andrea paz via Cin:
>> I did the following test:
>> NOTE: I use SAR as pixel aspect ratio i.e. SAR= Sample aspect ratio. I
>> use PAR as frame aspect ratio i.e. PAR= Picture aspect ratio. I use
>> PAR=W/H.
>> I took the following 4 videos:
>> Source_1:
>> bd.m2ts; 1440x1080; SAR 1:1; DAR 4:3
>> Compositor: Display stretched vertically; square px.
>> Source_2:
>> 5sec_dv01_03.dv; 720x576; SAR 16:15; DAR 4:3
>> Compositor: Display corrected; px nearly square.
>> Source_3:
>> 5sec_hdv01_04.m2t.ts; 1440x1080; SAR 4:3; DAR 16:9
>> Compositor: Correct display; rectangular px.
Just curious here:
Why and where did you get the extra file extension .ts?
Sony's extension for hdv has been .m2t, when hdv was transfered via 
i.LINK (IEEE 1394) from tape to Harddisk.
Though I think some other camcorder fabricators possibly used .ts or 
other instead.

>> Source_4:
>> bd_2.m2ts; 1920x1080; SAR 1:1; DAR 16:9;
>> Compositor: Correct display; square px.
> Just a short comment to the above:
> If Source_1 results from HDV 1440x1080 (check the video file with 
> ffprobe), I think it should have the same parameters as
> Source_3:
> 5sec_hdv01_04.m2t.ts; 1440x1080; *SAR 4:3; DAR 16:9
> *
>> I created a project (empty) 1440x1080; DAR=16:9  [SAR can be
>> calculated from: SAR = 16:9 / 4:3 = 1.3333 i.e. 4:3]
>> I imported 4 source files into Resources window.
>> What I notice in the Compositor is:
>> source_1 (same WxH; different SAR; different DAR) ==> non-square
>> Pixels (px); correct display; no crop/pad.
>>           Since WxH are the same the display remains correct. But since
>> the DARs are different then the aspect ratio changes adjusting to that
>> of the project (from 4:3 to 16:9). As a result the pixels enlarge
>> (similarly, adjusting to the design SAR: from 1:1 to 4:3), but without
>> crop/pad because they do not change the No. of pixels, but simply
>> those that are there extend horizontally.
>> source_2 (different WxH; different SAR; different DAR) ==> non-square
>> Pixels; flattened display; pad.
>>           The worst case because all aspect ratios are different
>> between source and project. Changing from smaller WxH_source to larger
>> WxH_project results in a pad i.e., an addition of side black bands.
>> Going from DAR 4:3 to 16:9 also results in a change in aspect ratio.
>> As in the case of source_1 the pixels stretch horizontally to change
>> from 16:15 to 4:3. The black sidebands arise precisely from the
>> extension of pixels that is not sufficent to fill the DAR_project; the
>> missing pixels are black and in such numbers as to fill the rest of
>> the project format.
>> source_3 (same WxH; same SAR; same DAR) ==> non-square Pixels; correct
>> display; no crop/pad.
>>           The best case since all aspect ratios are equal. The
>> rectangular pixels of the source are found to be the same in the
>> project, as are the DAR and the number of pixels of WxH. In fact, the
>> format of the project is the same as that of the source.
>> source_4 (differentWxH; different SAR; same DAR) ==> non-square
>> Pixels; flattened display; crop.
>>           Because of WxH_source > WxH_project we will have a crop, even
>> though the DAR is the same. This is because we go from DAR 1:1 to SAR
>> 4:3 so the pixels are forced to extend horizontally. Since the DAR is
>> the same there must be a crop of the source to fit within the smaller
>> WxH of the project.
>> So:
>> same WxH ==> Correct display.
>> WxH_source < WxH_project ==> flattened display; pad.
>> WxH_source > WxH_project ==> flattened display; crop.
>> SAR ==> determines the horizontal size of the pixels (only the
>> horizontal base). It is the first of the factors that adapt the
>> WxH_source to the WxH_project.
>> DAR ==> determines the shape of the frame. It is the second of the
>> factors that adapt the WxH_source to the WxH_project.
>>  From Set Format you set the design (WxH and DAR) at this point the
>> sources will have to adapt to this format, either by changing DAR or
>> by changing the pixel shape via SAR.
>> Do the results and explanations sound right to you?
>> I leave the link if anyone wants to try the EDL and the four videos:
>> https://www.dropbox.com/scl/fi/hvltphw3yq76mkquok1wq/Archivio.tar.gz?rlkey=bxko4ee6z0awr4epusnpyj8p5&dl=0
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