# Interlaced Video Testing
To test timing of the fields and ensuring they are received in a specific sequence, do the following:
1\. Install NDI Analysis Tool from ndi.video
2\. Ensure the tested device is outputting an Interlaced signal
3\. Run Analysis Tool in Command Prompt with the following command example:
```
NDIAnalysis.exe /source:"My Source (Channel 1)" /csv:"my source.csv" /time:300
```
\
Please note: Change **“/source:”My Source…”** to the device’s interlaced output, and change **/csv:”my source.csv”** to a specified file directory (for example:
```
NDIAnalysis.exe /source:"NDIHX Camera (Channel 1)" /csv:" C:\NDIAnalysisOutput\interlaced.csv" /time:300.
```
Also, it’s important to append the end of the Analysis command with **“/time:300”** so the file can have a definite end point.
4\. When the command finishes, examine the output file in a csv table editor like Excel- look at the B column, **titled “dTime (ms)”;** this measures the delta in milliseconds between when a field is sent and when it’s received- ideally, each field should be received at the same cadence- in the following example, each field is received roughly every 20ms on average.\
5\. If the timing of the fields don’t follow a regular cadence, it typically indicates that both the even and odd fields are sent by the device at the same time in the same packet of data and would look like this:
\
\
In the above example, you can see that Field 0 delta is typically higher than field 1; If field 0 and 1 in are averaged together it’s about 20ms, but due to the timing and capabilities of the receiver, a particular field may be overwritten by another (causing a ‘duplicated frame by the receiver) or a dropped frame as the receiver throws away what was received to render the next incoming video signal. In the end, this presents a poor user experience for both the customer’s equipment and NDI as a technology. The correct implementation of interlaced via NDI is to send the fields independently and in sequence to the SDK instead of delivering both fields to the SDK at the same time.
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