Standards conversion refers to the process of taking media authored for one frame rate, and converting it to be playable at a different frame rate. A variety of methods have been used with the original options being based upon very limited available technology, and through having to deal with analog acquired material. Over time the technology has improved but standards conversion remains a challenging process.
Emotion Systems have looked at the requirements for high quality conversion in a file-based world, including meeting with a number of Post Production facilities to discuss what they do, and what they would like to do. As a result we have developed methodology using our Engine product that gives very high quality results, and is now in use with customers in UK, Europe and USA. Here is our approach.
Treat the Video and Audio Separately
In files, the video and audio are contained in independent streams and it helps to consider them separately.
Although many different treatments have been applied to video to convert the frame rate, the consensus now is that the best approach is that where possible, to restamp the frame rate of the video so that it directly matches your requirement. The advantage is that the original quality is completely maintained, as there is no processing of the actual video data at all. Thus all the commonly seen artefacts of conversion processing are absent. Of course the duration of the video will increase or decrease, depending on the frame rate change that has been applied. This technique is only applicable to certain formats, such as converting from 24P to 25P, or vice versa. It is not possible to use this technique to change from interlaced to progressive video.
At the moment a third party tool has to be used to change the video frame rate, but this feature will be added to Engine during Spring 2019, for selected formats where processing of the video is not required.
Since the video duration has changed, the original audio will either be too long or too short. Engine’s Pitch & Duration module can be used to adjust the duration, and without changing the pitch from the source material.
The Pitch & Duration module is configured simply by selecting the source and destination frame rates that apply to the video, then the software calculates how to adjust the audio to match the new video duration. We use a high quality algorithm especially designed for this kind of application, and in tests with customers, it was possible to convert the audio several times before the editors were able to detect any processing artefacts.
Loudness Compliance is ubiquitous these days, and you would normally want to apply correction to the audio once the duration has been adjusted, to guarantee a compliant output. In Engine, you would simply create a multi-stage workflow, as shown below.
Following the suggested methodology using Engine will let you carry out certain framerate conversions, maintaining the original video quality whilst also providing impeachable audio to match, and you can do this in a totally automated workflow. Contact firstname.lastname@example.org for more information.