If i package a 480p video (480x854), (or any video which has different PAR than its width/height)
GPAC produces the wrong PAR and SAR values in the adaption set.
I use the following command:

```bash
gpac 
-i video.mp4:gpac:#PAR=16/9
-o dash.mpd:profile=dashavc264.onDemand:dual:cmaf=cmf2:styp:sfile:bs_switch=both:segdur=15:sbound=closest
```
It produces incorrect output:
```xml
<AdaptationSet segmentAlignment="true" maxWidth="854" maxHeight="480" maxFrameRate="60" par="427:240" lang="eng" startWithSAP="1" subsegmentAlignment="true" subsegmentStartsWithSAP="1">
  <Representation id="0" mimeType="video/mp4" codecs="avc1.64001F" width="854" height="480" frameRate="60" sar="1:1" bandwidth="1035863">
    <BaseURL>video_track1_init.mp4</BaseURL>
    <SegmentBase indexRangeExact="true" indexRange="970-1013">
      <Initialization range="0-941"/>
    </SegmentBase>
  </Representation>
</AdaptationSet>
```

As you can see, GPAC has set the following PAR and SAR values:
```ini
AdaptationSet@par = 427:240
Representation@sar = 1:1
```
These values are wrong, because i specified a PAR of 16:9 at the command line, and the SAR should be calculated from that. Allthough these values will technically work, they will causes conflicts if multiple representations are used.

Lets take a look at what the DASH-IF guidelines [[source]](https://dashif-documents.azurewebsites.net/DASH-IF-IOP/master/DASH-IF-IOP.html#video-constraints) say about that:

> Note: `@width` and `@height` indicate the number of encoded pixels. `@par` indicates the final intended display aspect ratio and `@sar` is effectively the ratio of aspect ratios (ratio of `@width` x `@height` to `@par`).
>
> Given a coded picture of 720x576 pixels with an intended display aspect ratio of 16:9, we would have the following values:
> `@width`=720
> `@height`=576
> `@par`=16:9
> `@sar`=45:64 (720x576 is 5:4, which gives `@sar`=5:4/16:9=45:64)

 So, applying this to our example, the correct values (according to DASH-IF) should be:
```ini
AdaptationSet@par = 16:9
Representation@sar = 1281:1280 # is calculated using (width/height)/par , in this case: (854/480)/(16/9)
```

I hope i explained the issue detailed enough :)
[BUG] Aspect ratios are handled incorrectly by GPAC when PAR is different than width/height
This is a GitHub Issue
repo:gpac
owner:gpac
Title : [BUG] Aspect ratios are handled incorrectly by GPAC when PAR is different than width/height
Issue date:

--- start body ---
If i package a 480p video (480x854), (or any video which has different PAR than its width/height)
GPAC produces the wrong PAR and SAR values in the adaption set.
I use the following command:

```bash
gpac 
-i video.mp4:gpac:#PAR=16/9
-o dash.mpd:profile=dashavc264.onDemand:dual:cmaf=cmf2:styp:sfile:bs_switch=both:segdur=15:sbound=closest
```
It produces incorrect output:
```xml
<AdaptationSet segmentAlignment="true" maxWidth="854" maxHeight="480" maxFrameRate="60" par="427:240" lang="eng" startWithSAP="1" subsegmentAlignment="true" subsegmentStartsWithSAP="1">
  <Representation id="0" mimeType="video/mp4" codecs="avc1.64001F" width="854" height="480" frameRate="60" sar="1:1" bandwidth="1035863">
    <BaseURL>video_track1_init.mp4</BaseURL>
    <SegmentBase indexRangeExact="true" indexRange="970-1013">
      <Initialization range="0-941"/>
    </SegmentBase>
  </Representation>
</AdaptationSet>
```

As you can see, GPAC has set the following PAR and SAR values:
```ini
AdaptationSet@par = 427:240
Representation@sar = 1:1
```
These values are wrong, because i specified a PAR of 16:9 at the command line, and the SAR should be calculated from that. Allthough these values will technically work, they will causes conflicts if multiple representations are used.

Lets take a look at what the DASH-IF guidelines [[source]](https://dashif-documents.azurewebsites.net/DASH-IF-IOP/master/DASH-IF-IOP.html#video-constraints) say about that:

> Note: `@width` and `@height` indicate the number of encoded pixels. `@par` indicates the final intended display aspect ratio and `@sar` is effectively the ratio of aspect ratios (ratio of `@width` x `@height` to `@par`).
>
> Given a coded picture of 720x576 pixels with an intended display aspect ratio of 16:9, we would have the following values:
> `@width`=720
> `@height`=576
> `@par`=16:9
> `@sar`=45:64 (720x576 is 5:4, which gives `@sar`=5:4/16:9=45:64)

 So, applying this to our example, the correct values (according to DASH-IF) should be:
```ini
AdaptationSet@par = 16:9
Representation@sar = 1281:1280 # is calculated using (width/height)/par , in this case: (854/480)/(16/9)
```

I hope i explained the issue detailed enough :)
--- end body ---

The issue describes incorrect handling of aspect ratios in GPAC when the Pixel Aspect Ratio (PAR) differs from the width and height of the video. The output generated by GPAC does not reflect the specified PAR, which can lead to conflicts in multi-representation scenarios. This could potentially cause playback issues or misinterpretation of video properties by clients that rely on accurate aspect ratio information.