Re: [MMUSIC] Remarks from today

[Ted Hardie <[e-mail]>]

Hi,

Some further comments in-line.

On Thu, Apr 14, 2011 at 11:21 PM, Bert Greevenbosch <
[e-mail]> wrote:

>  Hi Ted,
>
>
>
> My suspicion is that there are probably practical limits to some system's
> ability to either upsample or interpolate.  Would it make sense to add
> something to the 3dFormat line to indicate what the resulting per-view rate
> will be?  So that
>
> a=3dFormat:FP SbS
>
> had an additional parameter:
>
> a=3dFormat:FP SbS 30Hz
>
>  We could also consider using the SDP attribute "framerate" (RFC 4566).
> This attribute would give the frame rate of the 2D channel stream, but we
> can write in the draft that in the frame sequential case the frame rate per
> view is half of it.
>

The relevant text from RFC 4566 is:

a=framerate:<frame rate>

         This gives the maximum video frame rate in frames/sec.  It is
         intended as a recommendation for the encoding of video data.
         Decimal representations of fractional values using the notation
         "<integer>.<fraction>" are allowed.  It is a media-level
         attribute, defined only for video media, and it is not
         dependent on charset.

While I think it could be re-used here, it seems to me to make more sense to
use a separate indicator.  This is partly because it is more for the
decoder/upsampler/interpolation check (Can I upsample this to something
reasonable?  If not, don't select this choice).  And it's partly because I
worry a bit about the interaction with existing code.



>  Or do you want to indicate the target shutter glass frequency?
>
>
>

No, I think you're right that it's more likely that things will get adjusted
to a standard shutter speed by upsampling than they will change the shutter
speed.

regards,

Ted Hardie


> Best regards,
>
> Bert
>
>
>
>
>
> *From:* Ted Hardie [mailto:[e-mail]]
> *Sent:* 15 April 2011 02:49
>
> *To:* Bert Greevenbosch
> *Cc:* [e-mail]; [e-mail]
> *Subject:* Re: [MMUSIC] Remarks from today
>
>
>
> On Wed, Apr 13, 2011 at 10:44 PM, Bert Greevenbosch <
> [e-mail]> wrote:
>
>  I agree, the 30Hz (per view) case would give a flickering effect. Since
> normal TVs have a frequency of 60Hz or more, for a similar quality with
> shutter glasses the frame rate should be 120Hz (=60 Hz/view) or more.
>
>
>
> But the receiver can also upsample the received signal to a higher display
> rate. For example, if it receives the following frame sequence at 30Hz/view:
>
>
>
> L1,R1,L2,R2,L3,R3,...,
>
>
>
> then it could display at 60Hz/view:
>
>
>
> L1,R1,L1,R1,L2,R2,L2,R2,L3,R3,L3,R3,....
>
>
>
> The receiver can also use some interpolation technique to generate the
> frames between L*k* and L(*k*+1).
>
>
>
> I think that in praxis the receiving device will process the received
> stream to make it fit the display system. This allows different
> types/standards of shutter glasses to be used, independent on the format in
> which the 3D stream was received. It also allows other display types such as
> polarisation or autostereoscopic displays.
>
>
>
>
> My suspicion is that there are probably practical limits to some system's
> ability to either upsample or interpolate.  Would it make sense to add
> something to the 3dFormat line to indicate what the resulting per-view rate
> will be?  So that
>
> a=3dFormat:FP SbS
>
> had an additional parameter:
>
> a=3dFormat:FP SbS 30Hz
>
>
>    *>I know only know one manufacturer's system at all well, and my
> understanding is that the timing signals which synchronize them are really
> matching the frame start times to the shuttering, but don't adjust the frame
> rates.  Are there glasses which can modify the rate substantially as well?
> *
>
>
>
> Can you please explain a bit more about the system you are referring too,
> especially about not modifying the frame rate? Do you mean the frame rate
> between the TV screen and the signalling device (that transmits the signal
> to the shutter glasses) or the frame rate of the video stream as it is
> received before it is decoded (by the codec)?
>
>
>
>
> I probably should have said "shuttering rate", sorry.  I mean that it
> matches the shutters to the alternating left and right view, but that the
> shuttering rate is consistent (resulting in 60Hz per view, in this case).
>
> regards,
>
> Ted Hardie
>