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Old July 14th 17, 09:29 AM posted to uk.tech.digital-tv
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Default BT/Plusnet TV Recorder (DTR-T2100)

"thesimpsons" wrote in message
...
When playing back an off air recording, if I select fast forward the
screen displays a perfect speeded up image.
If playing back a recording from an internet channel, fast forward
displays "snap shots" of the speeded up image.
Just wondering why this should be, it's the same on both a ten year
Panasonic and a recent Sony TV.


Different types of compression.

SD TV uses MPEG which requires comparatively little computational effort to
decode - so the decoder can do every single frame even at faster than normal
speed, so you get smooth motion.

Many videos on the internet (eg Youtube) use MP4/H264 compression which
requires a lot more processing and the decoder can't display every frame at
faster than normal, so you get every nth frame and jerky motion. HD
television (including SD channels on a DVB-T2 "HD" multiplex) also uses
H264.

I have seen this difference when I use VideoRedo to edit out commercials
from my recordings on my PC: SD can scrub through at any speed, whereas HD
lags and "gets stuck" if you try to move the programme position too quickly.

This is one of the downsides of H264 - it produces smaller files but they
are more computational-intensive to decode so most decoders can't manage
faster-than-normal playing.