1080i vs. 720p

[ppppenguin]

Originally Posted by andy

I believe the main reason they don't do that is because of the audio, and for compatibility when editing. You can't just playback digital audio off speed without creating problems, and resampling would be a nightmare (particularly for DD and dts). It would also cause problems when editing since you can't easily make a VCR or other old source play faster.

Changing digital audio data rate is routine and commonplace. In dedicated gearbox chips, in software or in programmable logic. The ratio between input and output sampling frequencies can be arbitrary, it doesn't have to be a simple x/y ratio.

For older sources at 59.94Hz you ingest them into your digital editing system and replay them at 60Hz. If you need to transmit 60Hz programmes at 59.94Hz for compatibilty with with legacy NTSC systems then digital playoout systems can do this too.

old_tv_nut's comment about digital islands is true. But for quite a few years production and editing has been entirely digital and computer based. Legacy material on tape is ingested before being used and can be readily converted to whatever standard is required.