I’ve found the answer to this and am posting just to assist others
I have 2 v4k’s and 2 rapi3s
problem does not occur on raspi3 even with Hardware acceleration
on the V4k if hardware acceleration is enabled then fast forwarding at any speed above 2x will result in the frame freezing and you cannot restart play
Rewinding always causes a freeze up
However disabling the amcodec acceleration results in normal PVR behaviour
Strangely the raspi’s behave correctly even though they have hardware acceleration (a different one of course OMXPI and MMAL)
JM
PS on one Vero4k I can fast forward with Hardware acceleration enabled and it only occasionally freezes BUT the playback resumes usually after 30-60 seconds (not very usable)
Rewind freezes more frequently - the minutes rewound does not update . Sometimes the playback resumes where it should and sometimes it stays frozen
All better if no hardware acceleration but puzzled by the performance of two identical Vero4k
I can partly confirm the behaviour of the Vero 4k with active hardware acceleration and the mkv videos (h264) I used for tests:
- fast forwarding is not smooth but I can resume at any point of time
- fast rewinding simply stops the screen picture but you see the timestamp walking back in time; on try to resume I see a short “buffering” message but the screen picture stays frozen although the timestamp starts to continue in normal speed
Since it is so easy to reproduce, here no debug log etc. … but let me know if you need this neverthless.
I’m using a Full HD 1920x 1080 plasma TV and audio passthrough.
Thanks for the report.
As you’ve noted, the HW acceleration implementations on Pi and Vero 4K are different, and as such, they can behave differently.
Increasing the buffer size in advancedsettings.xml might improve this. We are planning to use a larger buffer size in a future update.
The rewinding issue is caused by amcodec and it needs some more work
Sam
You’re welcome
Even with the acceleration off the rewind is ‘troublesome’ - in the first place at any speed above 2x it fails to show the seconds counter so it is difficult to guess how far one has rewound.
Anyway I am sure you can sort that in a future edition
I’ll have a look at the buffer and see if that has an effect on the counter and report back
Yes – that suggests buffer to me.
Being worked on
Sam
While not solving your problem, if you want to know how far you jumped I wonder why you not just use step forward/backward instead of fast forward/backward
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@sam_nazarko - see what happens when you have FFWD and RWD buttons on a remote ! 
Fix it with some Volume control and that will stop most complaints.
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Yes the step forward (right/left arrows on v4k remote) are more controllable but worth mentioning this as it is a function which is supposed to work but doesn’t.
@wrxtasy dont quite know what you mean here (your point to @sam_nazarko)
Nor about ‘fixing it with volume control’ Is this about the Vero4k’s rather limited but stylish remote?
FWIW I have two remotes - the V4k which I like because of the rf interface but clearly has sacrificed volume control AND I have an old IR MC remote - the issue is the same regardless of which is used to rewind or fast forward