Visualize the quality of your video conversions

VizDiff is a simple but unique application designed to visually represent the quality of your video conversions. Simply drag-and-drop a source clip into the clip1 panel, then drag-and-drop a video conversion from that clip into the clip2 panel and "compare!".

VizDiff then processes the two clips and creates an A-B mix from both. When you establish a 50/50 mix of any original digital signal with a negative image of the same signal - the resulting visual differences are the errors generated by the conversion encoding. A blank image with no notable visual differences indicates a very high degree of quality and accuracy in the process

Fig 1 - example of high-quality conversion analysis

Fig 2 - example of highly compressed conversion analysis

Fig 3 - Original clip

Both analysis examples above were generated from conversions of the same source clip (Fig 3) - Fig 1 shows the analysis of a ProRes 4:4:4 conversion - Fig 2 shows the analysis of an MP4 conversion with heavy compression. Notice how the Fig 1 shows no discernible detail - this indicates that there is a very close match between the compared clips. The analysis in Fig 2 shows serious compression artifacts as well as color mismatch due to low bitrate and low-quality codec rendering


The more detail visible in the comparison, the less quality of conversion when compared to the original clip


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When Quality Counts

VizDiff provides unique tools for checking conversion quality. Here's how it works:

VizDiff first takes the two clips selected for comparison and creates a video mix - negating one video in the process. This process creates an overall gray video that shows only the differences between clips. These differences can be hard to spot due to lacking contrast and detail - so VizDiff also provides an enhanced view of the analysis for more detailed scrutiny. This is shown in the analysis viewer

Frame from unaltered analysis video

Same frame with enhancement curve applied

Note that the above frames were generated from a high-quality conversion. Note that no colors present indicates very high fidelity of color conversion - the dark areas in the analysis indicate the conversion from 4:2:0 to 4:4:4 color space and interpolation (which fills in the missing colors between color spaces) - this is a good thing ; )

In addition, VizDiff provides RGB Parade waveforms for both clips under comparison to help spot obvious compression artifacts and color disparities. In the analysis below you can actually see critical differences between the RGB waveforms

The bottom left viewer shows the source clip (clip 1) and scrollbar. Use this to scrub through the clip to select frames. Each frame will repaint the RGB Parade traces and also show the representative frame from the generated comparison video - with an enhancement curve applied to help better visualize any discrepancies. This curve simply rolls off the high and low values of light which remain outside of the analysis mix spectrum, while the pertinent data remains unaltered. RGB parade traces are derived from the original video clips 1 & 2 - not from analysis video

Once an analysis is complete you can play the comparison video itself via the button on the main interface. This will show the comparison video without enhancement

NEW! - You can now elect to view both source and comparison videos side-by-side in the scope viewer

You will also find icons at the bottom of the scopes panel for grabbing full-size TIFF images from the frame currently in view - one for the original source clip and one for the enhanced frame under analysis. This makes it easier to compare between different codec analyses

Note - when running a comparison analysis, scrolling in the scope panel is disabled - once the comparison is completed control will return


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A Note About Sound

Compare Oranges to Oranges...

In order to keep your conversion analyses honest, it is best to setup the conversion (to be tested) - to convert without audio. Some audio formats actually embed a time offset in the video clip in order to maintain audio / video sync throughout the converted video. This may cause a delay in the first frame - which will in turn offset the analysis and consequently show false positives

You may notice a slight difference in the durations shown for source clip opposed to comparison clip. This is also an audio artifact - it is common for and audio track not to match 100% with the last video frame - causing a slight discrepancy in durations. This time should be within merely hundredths of a second - larger discrepancies may indicate other transcoding problems (extra frames, wrong framerate, etc.


Example of analysis with audio offset error


VizDiff is free to use for any purpose and does not require license

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