Slow Motion and Frame Advance missing?

Most Blu-ray & DVD players, PVRs, and even VCRs (!) as well as VLC media player have no  problem providing high quality search and slow motion in most video files – why not WDTV hub? As a new owner I was surprised and dismayed at the lack of slow motion, frame advance, and high quality search with frequent screen refresh. What’s the problem – not enough processing power? I imagine most movie fans find these features handy (or indispensable).

Your post sounds more like a good Feature Request; best placed in the Ideas Exchange section. This way someone from WD will be sure to see it and will allow more users to support your idea. However, I would first search and make sure that there are no other active Feature Requests suggesting the same or similar improvements. If there is, then you could add your post and vote on it.

Live Hub Ideas


dociso wrote:


VLC media player has no  problem providing high quality search and slow motion both forward and back in most video files – why not WDTV hub?

Well, actually VLC does have problems.

VLC was designed to (and advertises that it will) play bad/broken files.  Thus, it tends to ignore specs and do things its own way.

Technically, for any video stream, playback is only supposed to start at a sequence header, so that all the proper values for that sequence can be read and applied.

You don’t notice this with things like DVDs, because the sequences are 15 frames long… if you tell it to play back at a certain point, you can’t tell which frame it’s actually starting on… playback starts at the start of a sequence.

But, other encodings can use longer sequences.  In fact, the entire file can be one sequence.

The WDTV devices only support playback at the nearest sequence to where playback has been requested – even if you specify an exact frame timecode in a chapter mark, playback of that chapter will generally NOT begin on that frame… it will be at the nearest new sequence to that frame, so that all the correct settings for that sequence can be read.

VLC ignores this requirement – you can start playback anywhere… but unless you do start at a new sequence, the video output WILL generally be garbled until a new sequence header and I-frame is found.  If the sequence is long, the screen can remain garbled for a long time.  Again, if the sequences are short, you often don’t even notice – it totally depends on the encoding.

It doesn’t seem to be in WD’s interests (regardless of whether the chip has the processing power or not) for playback to be “mangled” every time you FF or REV.  It seems to me as if WD is better off sticking to the specs and playing back from the headers, as is spec’d out.  That way, the video is always going to look right when it plays.  But the downside is that playback may not be where you want it to be.  Some bad encodes have very long sequences, and if you FF or REV, sometimes the actual playback point is 10 minutes off (or more).  But the way to avoid that is to just not make bad encodes – not to break proper playback.  Because those same bad encodes don’t play “properly” in VLC either – the only difference is that playback starts where you ask instead of where it “should”, but/so the screen is garbled.

And again, the screen updates when FFing and REWing are problematic.  The WDTVs just don’t have the same processing power as a PC… they can’t really generate frames on the fly, and pretty much have to rely on I-frames.  If you try to FF a file that has short sequences on a WDTV, then you do get frequent screen updates, just like with any other DVD player.  But, if you try to FF/REV a file with long sequences, then there aren’t nearly as many I-frames to work with and the screen updates are much fewer and farther apart.  The WDTV simply doesn’t have any frames to display in the interim, and it can’t really generate intermediate frames like VLC can.  So again, the lack of “smoothness” is totally dependant on your encoding.  If you create (or download) files with very long sequences, then there just won’t be many frames for the WDTV to display while you’re trying to scan through and it will display what it physically can.

But you can’t really blame the WDTV for properly handling poor encodes.  It’s much better to just make decent encodes to start with, and then the files will play (and FF/REV) as you expect them to.  Or, if you insist on using bad encodes, then it’s better to use something like VLC that advertises support for bad/broken encodes, instead of a hardware player that expects the standards to be met.

Trancer, thanks – it appears there are similar feauture requests already in place.


Wow! Thanks for all the info, you obviously know a lot about this stuff – I don’t. However, I have not noticed the garbled video in VLC that you describe. Do these issues also apply to slow motion?

I just tried several files in VLC, .avi and DVD.iso, and variable speed search forward and jump forward and back by various amounts are perfectly clear.

I also tried variable slow motion and frame advance, and again, clear as can be on .m2ts files as well.

I guess it just must be a lack of processing power in the hub. Maybe someday…!

As I say, it does depend on the encode, but I stand corrected –  just double-checked and it seems like VLC no longer behaves like I said it did. :cry:

What used to happen, if a chapter didn’t begin on a new sequence and an I-frame, or if you used the scroll bar to advance in the movie, when playback resumed, since VLC only had B-frames and P-frames to work with (the I-frames are basically a jpeg of the entire screen… the P- and B- frames are essentially only what’s changed from the last frame) it would draw the “changed” areas properly, but the “unchanged” areas would just be a matte gray… the screen would look funky until it got to the next I-frame, and then full pictures would again be shown.  This is what I was calling “garbled”.

But, I just checked.  I don’t know what update they changed that, but now it plays exactly like the WDTV does… it starts on the closest I-frame with a clear picture, and not exactly where you tell it to.

I can tell because some things I’ve added chaptering info to.  If I pick a certain chapter, playback on the WDTV would usually be 2 or 3 seconds on either side of the actual chapter point.  VLC used to start at the specified frame, but the screen would be garbled, as described above, until the next I-frame was encountered.  Now VLC starts at the same 2-3 second-off point that the WDTV does.  Since they changed this in VLC in one of the recent updates, the screen no longer ever gets mangled like I’d described.

Media Player Classic, on the other hand, still behaves poorly.  It will start on the exact time code, and it doesn’t garble the screen, but it messes up playback for me another way.  If I pick a chapter, or use the slider, then when playback resumes, there’s no picture at all, just audio, until the next sequence begins. :wink:  It apparently knows it doesn’t have the full picture information, so instead of generating a garbled screen, it just generates nothing.

But, because playback begins on the nearest sequence beginning on the WDTV, as it is supposed to, many people with pirated movies run into the odd effect of playback being up to 10 minutes off where they expect it.  Some of the pirated movies floating around have very long sequences.  So, someone’s merrily watching it, and goes to FF or REW 30 seconds, and when they push play, it starts playing like 2 minutes or 5 minutes or 10 minutes before or after the point they started FF/REW from.  Then they come here and complain that the WDTV won’t FF/REW properly, because when they go to FF 30 seconds ahead, playback resumes 5 minutes before the point they FF’d from. :wink:

Usually a DVD will have 15-frame sequences… so you have about a half second of “accuracy” when trying to random-access a playback point.

It seems as if the encodes that Handbrake makes for me has sequences that are about 5 seconds long (i.e. around 100 frames or so).  My “accuracy” is usually within a second or two of the expected point.

Some internet downloads (and PVR encodes) have much longer sequences.  Occasionally, a PVR encode is only one sequence, and can not be FF/REW at all… it can only be played straight through.

It shouldn’t affect slow-mo at all, on either VLC or the WDTV.  When the file’s playing, if you pause and then start advancing frames, it already has the full picture, so it makes no difference whether the next frame it reads is an I-frame or a P-frame or a B-frame… it can always generate the next frame with no garbling.

But, as I said, the 10 second and 30 second jumps you originally asked about, would work reasonably well with DVD material, and alright with Handbrake encodes, but would be utterly useless for a good deal of pirated material, due to the sequence lengths – playback simply can’t start properly where you’d expect it to.

I have just realized that the subject header “Re: JUMP 10 SEC FORWARD, 30 SEC FORWARD…” relates to a different thread. I originally posted my message in that thread, but it was moved here by an administrator including the subject line that isn’t really appropriate to my post. So I’ll edit it now.

I don’t know much about the technical stuff.

I just know that I have had slow motion and frame advance on every video playback device I can remember:

My current PVR, DVD player, and PS3. Even most of my VCRs (I’m old) had these features. So here we are in 2011 with the Latest Cool Toy, and I’m surprised that it’s missing that’s all.

If I’m told I can’t have them for whatever reason, I accept that. I’m sure someday these features will be added. :smiley:

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