[mythtv] Jitter with time stretch

[David Engel]

On Mon, Jul 16, 2018 at 10:47:53AM -0400, Peter Bennett wrote:
> 
> 
> On 07/15/2018 10:02 PM, David Engel wrote:
> > On Sun, Jul 15, 2018 at 07:05:21PM -0400, Peter Bennett wrote:
> > > On 07/15/2018 04:50 PM, David Engel wrote:
> > > > I found it!  In MythPlayer::SetFrameInterval(), the frame_interval and
> > > > avsync_predictor_enabled are getting set wrong because frame_period
> > > > passed in is wrong.  It is still set the 30fps equivalent instead of
> > > > the 60fps equivalent after the frame doubling in decoding.
> > > > 
> > > > After forcing frame_interval and avsync_predictor_enabled to the
> > > > correct values, I get smooth playback of my sample, 1080i content on
> > > > my 1080p TV at speed upto 1.90x.  At 1.95x, a little bit of
> > > > non-predicted adjustment is needed, but it's barely noticeable.  At
> > > > 2.00x, it a little more noticeable, but really isn't too bad.
> > > > 
> > > > On my 4k TV, the results aren't quite as good.  The video gets
> > > > noticeably jittry at 1.55x.  It seems the scaling from 1080 to 4k
> > > > impacts how fast the decoding and deinterlacing can go.  I wonder what
> > > > effect using Surface rendering would have on that.
> > > > 
> > > > Note that the above was all done with using the old numbers of buffers
> > > > (vbuffers.Init(31, true, 1, 12, 4, 2)).  I'm going to see how far I
> > > > can reduce them without degrading the timestretching performance.
> > Things seem to be okay with the modified numbers of buffers
> > (vbuffers.Init(4, true, 1, 2, 2, 1)).  I have more TV watching, I mean
> > testing, to do, though. :)
> I am adding a line to only allocate the lower number of buffers if it is
> mediacodec. I found that using the smaller number on Linux with OpenGL
> profile turns playback into a slideshow with corrupted frames.
> > > > Finally, I don't have a proposed fix for the correct setting of
> > > > frame_interval and avsync_predictor_enabled yet.  I'll defer to those
> > > > of you more familiar with the MythPlayer setup for the time being.  It
> > > > probably needs to be tied into the code that Peter added to detect the
> > > > frame doubling during decoding.
> > > > 
> > > > David
> > > > 
> > > > 
> > > I agree - frame_interval needs fixing. We just need to be careful of not
> > > using the adjusted value when seeking, because for file access it uses the
> > > original frame number. For example in MythPlayer::UpdateFFRewSkip, I amnot
> > > quite sure what that is doing with it. I will go through and check all the
> > > places where frame_interval is used and see if I can get it right.
> > We could possibly get by with just a new variable that flags when the
> > decoder doubles the frame rate.  I think the modified frame_interval
> > is only needed in MythPlayer::SetFrameInterval() where
> > avsync_predictor_enabled is initialized and in MythPlayer::AVSync()
> > where avsync_predictor_enabled is checked and used.
> I already have a flag stored in the decoder and accessed from mythplayer
> using "decoder->GetfpsMultiplier()" It takes values 1 or 2, 1=normal,
> 2=doubled frames as with mediacodec.

Excellent!

> I am currently using fpsMultiplier only in AVSync where frame_delay is
> calculated from frame_interval. I need to take that out and change the
> calculation of frame_interval itself to use fpsMultiplier instead.

So are you going to make the avsync_predictor_enabled change then or
do you want me to do it?  I have time for it today.

David
-- 
David Engel
david at istwok.net