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Problems with Bob Playback

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greg.mythtv at optusnet

Jan 13, 2006, 11:01 PM

Post #1 of 11 (4465 views)
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Problems with Bob Playback

I have a problem with Changeset 8510 where playback gets severely jerky after a pause/play.

Some specifics:

Only appears to effect the bob deinterlacer (which is the most useful one IMHO)
I use PAL DVB in australia.
Is quite repeatable.
I am using svideo from an FX 5200.
Problem occurs for both Standard and libmpeg2 playback.
Skipping forward in playback does not appear to cause the problem.
Switching timestretch to 1.05 or 0.95 makes it smooth again, but switching back to 1.00 causes it to start jerking again.

I would be very interested to know if anyone else is seeing(or not seeing) this issue.
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rob.r at plutohome

Jan 14, 2006, 12:48 AM

Post #2 of 11 (4397 views)
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Re: Problems with Bob Playback [In reply to]

What does your frontend log/console output show when it's being jerky?

-----Original Message-----
From: mythtv-dev-bounces[at]mythtv.org [mailto:mythtv-dev-bounces[at]mythtv.org]
On Behalf Of greg.mythtv[at]optusnet.com.au
Sent: Friday, January 13, 2006 11:02 PM
To: mythtv-dev[at]mythtv.org
Subject: [mythtv] Problems with Bob Playback

I have a problem with Changeset 8510 where playback gets severely jerky
after a pause/play.

Some specifics:

Only appears to effect the bob deinterlacer (which is the most useful one
IMHO)
I use PAL DVB in australia.
Is quite repeatable.
I am using svideo from an FX 5200.
Problem occurs for both Standard and libmpeg2 playback.
Skipping forward in playback does not appear to cause the problem.
Switching timestretch to 1.05 or 0.95 makes it smooth again, but switching
back to 1.00 causes it to start jerking again.

I would be very interested to know if anyone else is seeing(or not seeing)
this issue.
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stutty at gmail

Jan 14, 2006, 1:45 PM

Post #3 of 11 (4384 views)
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Re: Problems with Bob Playback [In reply to]

On 1/14/06, greg.mythtv[at]optusnet.com.au <greg.mythtv[at]optusnet.com.au> wrote:
>
> I have a problem with Changeset 8510 where playback gets severely jerky after a pause/play.
>

I'm also seeing this occasionally in SVN 8482, also PAL DVB, Bob
deinterlace, two seperate Frontends show the same fault (My desktop
machine running Mandriva - no other changes except Myth upgrade, and
the Media PC, EPIA running Gentoo).

No other info yet though.

Paul
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lists at ebourne

Jan 14, 2006, 3:14 PM

Post #4 of 11 (4380 views)
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Re: Problems with Bob Playback [In reply to]

On Sat, 14 Jan 2006 18:01:54 +1100, greg.mythtv wrote:
> I have a problem with Changeset 8510 where playback gets severely jerky
> after a pause/play.
>
> Some specifics:
>
> Only appears to effect the bob deinterlacer (which is the most useful one
> IMHO) I use PAL DVB in australia.
> Is quite repeatable.
> I am using svideo from an FX 5200.
> Problem occurs for both Standard and libmpeg2 playback. Skipping forward
> in playback does not appear to cause the problem. Switching timestretch to
> 1.05 or 0.95 makes it smooth again, but switching back to 1.00 causes it
> to start jerking again.
>
> I would be very interested to know if anyone else is seeing(or not seeing)

I'm getting the exact same thing. I am also PAL DVB but UK. I am using VGA
@ 1360x768/60Hz via a Matrox G550. It's not jerky as in pausing, but
rather the picture is vibrating vertically by about a source pixel, at
about the frame rate, which also causes jerky movement. Almost like it's
drawing the bottom field above the top field. It also affects the OSD in
the same way, and I see this not just on over the air programming, but
also on DVDs using the internal player. PAL and NTSC dvds and ones that I
believe are progressive too.

Anything other than timestretch 1.0 works great, just at 1.0 it is broken.
From my laptop (ATI Radeon Mobility X700, VGA @ 1024x768/60Hz), with
exactly the same compile, it seems fine.

I am running r8586 on FC4. Thanks for reporting this Greg, mine is a new
LCD set I got today and the awful picture was rather concerning.
Fortunately I spotted your mail on the list & tried with timestretch. I'm
a lot happier now. :)

Cheers,

Martin.

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mtdean at thirdcontact

Jan 14, 2006, 6:12 PM

Post #5 of 11 (4369 views)
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Re: Problems with Bob Playback [In reply to]

Martin Ebourne wrote:
> Anything other than timestretch 1.0 works great, just at 1.0 it is broken.
>
If using timestretch, bob deinterlacing is disabled, so that would
explain why you don't see the problem with timestretch. :)

Mike
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greg.mythtv at optusnet

Jan 14, 2006, 9:34 PM

Post #6 of 11 (4399 views)
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Re: Problems with Bob Playback [In reply to]

>> Subject: [mythtv] Problems with Bob Playback
>>
>>
>> I have a problem with Changeset 8510 where playback gets severely jerky
>> after a pause/play.
>>
>> Some specifics:
>>
>> Only appears to effect the bob deinterlacer (which is the most useful
>> one
>> IMHO)
>> I use PAL DVB in australia.
>> Is quite repeatable.
>> I am using svideo from an FX 5200.
>> Problem occurs for both Standard and libmpeg2 playback.
>> Skipping forward in playback does not appear to cause the problem.
>> Switching timestretch to 1.05 or 0.95 makes it smooth again, but
>> switching
>> back to 1.00 causes it to start jerking again.

> Rob R <rob.r[at]plutohome.com> wrote:
>
> What does your frontend log/console output show when it's being jerky?

This is what I found with mythfrontend -v playback:

mythtv[at]mythtv:~$ cat frontend.log
2006-01-15 08:56:14.719 Using runtime prefix = /usr
2006-01-15 08:56:14.748 New DB connection, total: 1
2006-01-15 08:56:14.755 Total desktop dim: 720x576, with 1 screen[s].
2006-01-15 08:56:14.759 Using screen 0, 720x576 at 0,0
2006-01-15 08:56:14.765 Enabling Settings Cache.
2006-01-15 08:56:14.766 Clearing Settings Cache.
2006-01-15 08:56:14.766 user: 105 effective user: 105 before privileged thread
2006-01-15 08:56:14.767 user: 105 effective user: 105 after privileged thread
2006-01-15 08:56:14.768 user: 105 effective user: 105 run_priv_thread
2006-01-15 08:56:14.770 Current Schema Version: 1121
2006-01-15 08:56:14.772 mythfrontend version: 0.19.20051208-1 www.mythtv.org
2006-01-15 08:56:14.772 Enabled verbose msgs: important general playback
2006-01-15 08:56:14.935 max_width: 720 max_height: 576
2006-01-15 08:56:14.937 lang0: eng
2006-01-15 08:56:14.938 lang: eng
2006-01-15 08:56:14.945 lang1: eng
2006-01-15 08:56:14.946 lang: eng
2006-01-15 08:56:15.038 Total desktop dim: 720x576, with 1 screen[s].
2006-01-15 08:56:15.041 Using screen 0, 720x576 at 0,0
2006-01-15 08:56:15.068 Switching to square mode (blue)
2006-01-15 08:56:15.386 New DB connection, total: 2
2006-01-15 08:56:15.389 Joystick disabled.
2006-01-15 08:56:15.401 Clearing Settings Cache for 'Language'.
2006-01-15 08:56:15.402 Clearing Settings Cache.
2006-01-15 08:56:15.431 Registering Internal as a media playback plugin.
2006-01-15 08:56:15.465 Registering MythDVD DVD Media Handler as a media handler
2006-01-15 08:56:15.466 Registering MythDVD VCD Media Handler as a media handler
2006-01-15 08:56:16.597 Registering MythMusic Media Handler as a media handler
SIP listening on IP Address 10.1.1.24:5060 NAT address 10.1.1.24
SIP: Cannot register; proxy, username or password not set
2006-01-15 08:56:17.095 Starting media monitor.
2006-01-15 08:56:20.665 All Programs
2006-01-15 08:56:20.928 Connecting to backend server: 127.0.0.1:6543 (try 1 of 5)
2006-01-15 08:56:20.936 Using protocol version 22
2006-01-15 08:56:21.568 TV: Attempting to change from None to WatchingPreRecorded
2006-01-15 08:56:21.569 RingBuf(/myth/tv/1007_20060114142400.mpg): OpenFile(/myth/tv/1007_20060114142400.mpg, 6)
0: start_time: 2397.503 duration: 115.916
1: start_time: 4281.229 duration: 115.910
2: start_time: 4281.245 duration: 115.916
stream: start_time: 26638.927 duration: 22218.418 bitrate=415 kb/s
2006-01-15 08:56:21.764 AFD: Stream #0, has id 0x1284 codec id DVB_VBI, type Data at 0x0x81f4340
2006-01-15 08:56:21.765 AFD: data codec (Data)
2006-01-15 08:56:21.765 AFD: Stream #1, has id 0x1282 codec id MP3, type Audio at 0x0x8256ff0
2006-01-15 08:56:21.765 AFD: Looking for decoder for MP3
2006-01-15 08:56:21.790 AFD: Opened codec 0x823cb40, id(MP3) type(Audio)
2006-01-15 08:56:21.790 AFD: Audio Track #1 is A/V stream #1 and has 2 channels in the English language(6647399).
2006-01-15 08:56:21.790 AFD: Stream #2, has id 0x1281 codec id MPEG2VIDEO, type Video at 0x0x823ce80
2006-01-15 08:56:21.795 detectInterlace(Detect Scan, Detect Scan, 25, 576) ->Interlaced Scan
2006-01-15 08:56:21.795 Interlaced: Interlaced Scan video_height: 576 fps: 25
2006-01-15 08:56:21.795 AFD: Looking for decoder for MPEG2VIDEO
2006-01-15 08:56:21.795 AFD: Opened codec 0x87816e0, id(MPEG2VIDEO) type(Video)
2006-01-15 08:56:21.795 RingBuf:CalcReadAheadThresh(15256 KB) -> threshhold(750 KB) readblocksize(250 KB)
2006-01-15 08:56:21.795 AFD: Selected track 1: English MP2 2ch (A/V Stream #1)
2006-01-15 08:56:21.795 AFD: Initializing audio parms from audio track #1
2006-01-15 08:56:21.795 AFD: Audio format changed
from id(NONE) -1Hz -1ch 0bps ; id(NONE) -1Hz -1ch 0bps
to id( MP3) 48000Hz 2ch 16bps ; id( MP3) 48000Hz 2ch 16bps
2006-01-15 08:56:21.797 Opening audio device '/dev/dsp'.
2006-01-15 08:56:21.798 Opening OSS audio device '/dev/dsp'.
2006-01-15 08:56:21.807 Resyncing position map. posmapStarted = 0 livetv(0) watchingRec(0)
2006-01-15 08:56:21.869 Position map filled from DB to: 32196
2006-01-15 08:56:21.870 SyncPositionMap prerecorded, from DB: 2684 entries
2006-01-15 08:56:21.871 SyncPositionMap, new totframes: 32196, new length: 1287, posMap size: 2684
2006-01-15 08:56:21.872 AFD: Position map found
2006-01-15 08:56:21.872 AFD: Successfully opened decoder for file: "/myth/tv/1007_20060114142400.mpg". novideo(0)
2006-01-15 08:56:21.880 VideoOutputXv: ctor
2006-01-15 08:56:21.890 Over/underscan. V: 0, H: 0, XOff: 0, YOff: 0
2006-01-15 08:56:21.896 Snapping width to avoid scaling: dispwoff 720, dispxoff: 0
2006-01-15 08:56:21.897 Image size. dispxoff 0, dispyoff: 72, dispwoff: 720, disphoff: 432
2006-01-15 08:56:21.898 Image size. imgx 0, imgy: 0, imgw: 720, imgh: 576
2006-01-15 08:56:21.898 VideoOutputXv: Pixel dimensions: Screen 720x576, window 720x576
2006-01-15 08:56:21.899 VideoOutputXv: Estimated display dimensions: 244x195 mm Aspect: 1.25128
2006-01-15 08:56:21.899 VideoOutputXv: Estimated window dimensions: 244x195 mm Aspect: 1.25128
2006-01-15 08:56:21.901 VideoOutputXv: @ j=3 Looking for flag[s]: XvInputMask XvImageMask
2006-01-15 08:56:21.902 VideoOutputXv: Adaptor: 0 has flag[s]: XvInputMask XvImageMask
2006-01-15 08:56:21.903 VideoOutputXv: XVideo surface found on port 177
2006-01-15 08:56:21.904 VideoOutputXv: XVideo Format #0 is 'YUY2'
2006-01-15 08:56:21.905 VideoOutputXv: XVideo Format #1 is 'YV12'
2006-01-15 08:56:21.905 VideoOutputXv: XVideo Format #2 is 'UYVY'
2006-01-15 08:56:21.905 VideoOutputXv: XVideo Format #3 is 'I420'
2006-01-15 08:56:21.906 VideoOutputXv: Using XVideo Format 'I420'
2006-01-15 08:56:22.002 Snapping width to avoid scaling: dispwoff 720, dispxoff: 0
2006-01-15 08:56:22.002 Image size. dispxoff 0, dispyoff: 85, dispwoff: 720, disphoff: 405
2006-01-15 08:56:22.003 Image size. imgx 0, imgy: 0, imgw: 720, imgh: 576
2006-01-15 08:56:23.569 NVP: ClearAfterSeek()
2006-01-15 08:56:23.569 TV: StartPlayer(): took 1970 ms to start player.
2006-01-15 08:56:23.570 VideoOutputXv: ClearAfterSeek()
2006-01-15 08:56:23.571 VideoBuffers::DiscardFrames(0): AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
2006-01-15 08:56:23.571 VideoBuffers::DiscardFrames(0): AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA -- done
2006-01-15 08:56:23.574 Realtime priority would require SUID as root.
2006-01-15 08:56:23.575 TV: Changing from None to WatchingPreRecorded
2006-01-15 08:56:23.601 AFD: DoFastForward(57 (1), do discard frames)
2006-01-15 08:56:23.601 Dec: DoFastForward(57 (1), do discard frames)
2006-01-15 08:56:23.602 AFD: SeekReset(60, 0, do flush, do discard)
2006-01-15 08:56:23.602 AFD: SeekReset() flushing
2006-01-15 08:56:23.602 VideoBuffers::DiscardFrames(1): UAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
2006-01-15 08:56:23.602 VideoBuffers::DiscardFrames(): AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA -- done()
2006-01-15 08:56:23.602 VideoBuffers::DiscardFrames(1): AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA -- done
2006-01-15 08:56:23.603 NVP: ClearAfterSeek()
2006-01-15 08:56:23.603 VideoOutputXv: ClearAfterSeek()
2006-01-15 08:56:23.603 VideoBuffers::DiscardFrames(0): AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
2006-01-15 08:56:23.603 VideoBuffers::DiscardFrames(0): AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA -- done
2006-01-15 08:56:23.733 Using deinterlace method bobdeint
2006-01-15 08:56:23.836 nVidiaVideoSync: VBlank ioctl did not work, unimplemented in this driver?
2006-01-15 08:56:23.963 DRMVideoSync: Could not open device /dev/dri/card0, No such device or address
2006-01-15 08:56:23.967 OpenGLVideoSync: GLX extensions: GLX_EXT_visual_info GLX_EXT_visual_rating GLX_SGIX_fbconfig GLX_SGIX_pbuffer GLX_SGI_video_sync GLX_SGI_swap_control GLX_ARB_multisample GLX_NV_float_buffer GLX_ARB_get_proc_address
2006-01-15 08:56:23.968 OpenGLVideoSync: x,y -> 361, 289
2006-01-15 08:56:24.076 Using OpenGLVideoSync
2006-01-15 08:56:24.079 Set video sync frame interval to 40000
2006-01-15 08:56:24.079 Video sync method can't support double framerate (refresh rate too low for bob deint)
2006-01-15 08:56:24.079 Set video sync frame interval to 40000
2006-01-15 08:56:24.082 Using deinterlace method onefield
2006-01-15 08:56:24.096 Using audio as timebase
2006-01-15 08:56:24.096 Video timing method: SGI OpenGL
2006-01-15 08:56:24.097 Refresh rate: 40000, frame interval: 40000
2006-01-15 08:56:24.219 NVP: Video is 3.01892 frames ahead of audio, dropping frame.
2006-01-15 08:56:24.220 NVP: Video is 3.03292 frames ahead of audio, dropping frame.
'video_output' mean = '37773.65', std. dev. = '8150.90', fps = '26.47'
'video_output' mean = '39796.64', std. dev. = '1510.01', fps = '25.13'
2006-01-15 08:56:35.228 NVP: Changing speed to 0
2006-01-15 08:56:35.228 rate: 25 speed: 1 skip: 1 = interval 40000
2006-01-15 08:56:35.229 Set video sync frame interval to 40000
2006-01-15 08:56:36.140 NVP: Play( 1.0, normal 1, unpause audio 1)
2006-01-15 08:56:36.143 NVP: Changing speed to 1
2006-01-15 08:56:36.143 NVP: DoPlay: rate: 25 speed: 1 skip: 1 => new interval 39999
2006-01-15 08:56:36.144 Set video sync frame interval to 39999
2006-01-15 08:56:36.144 Set video sync frame interval to 39999
2006-01-15 08:56:36.146 Using deinterlace method bobdeint
2006-01-15 08:56:36.146 NVP: Stretch Factor 1, allow passthru
2006-01-15 08:56:36.340 NVP: Video is 3.71842 frames ahead of audio, dropping frame.
2006-01-15 08:56:36.343 NVP: Video is 5.22011 frames ahead of audio, dropping frame.
2006-01-15 08:56:36.345 NVP: Video is 6.11513 frames ahead of audio, dropping frame.
2006-01-15 08:56:36.351 NVP: Video is 6.54889 frames ahead of audio, dropping frame.
2006-01-15 08:56:36.353 NVP: Video is 6.66169 frames ahead of audio, dropping frame.
2006-01-15 08:56:36.356 NVP: Video is 6.50879 frames ahead of audio, dropping frame.
2006-01-15 08:56:36.373 NVP: Video is 6.16285 frames ahead of audio, dropping frame.
2006-01-15 08:56:36.376 NVP: Video is 5.75967 frames ahead of audio, dropping frame.
2006-01-15 08:56:36.379 NVP: Video is 5.22601 frames ahead of audio, dropping frame.
2006-01-15 08:56:36.381 NVP: Video is 4.59451 frames ahead of audio, dropping frame.
2006-01-15 08:56:36.397 NVP: Video is 3.8834 frames ahead of audio, dropping frame.
2006-01-15 08:56:36.399 NVP: Video is 3.1938 frames ahead of audio, dropping frame.
'video_output' mean = '46785.88', std. dev. = '93627.05', fps = '21.37'
2006-01-15 08:56:36.779 NVP: Video is 3.39006 frames ahead of audio, dropping frame.
2006-01-15 08:56:36.787 NVP: Video is 3.46756 frames ahead of audio, dropping frame.
2006-01-15 08:56:36.790 NVP: Video is 3.32568 frames ahead of audio, dropping frame.
2006-01-15 08:56:36.899 NVP: Video is 3.15353 frames ahead of audio, dropping frame.
2006-01-15 08:56:36.902 NVP: Video is 3.04015 frames ahead of audio, dropping frame.
2006-01-15 08:56:37.079 NVP: Video is 3.25408 frames ahead of audio, dropping frame.
2006-01-15 08:56:37.081 NVP: Video is 3.24058 frames ahead of audio, dropping frame.
2006-01-15 08:56:37.199 NVP: Video is 3.28066 frames ahead of audio, dropping frame.
2006-01-15 08:56:37.202 NVP: Video is 3.26051 frames ahead of audio, dropping frame.
2006-01-15 08:56:37.207 NVP: Video is 3.01413 frames ahead of audio, dropping frame.
2006-01-15 08:56:37.462 NVP: Video is 3.39121 frames ahead of audio, dropping frame.
mythtv[at]mythtv:~$

The interesting part seems to be this:

2006-01-15 08:56:24.079 Video sync method can't support double framerate (refresh rate too low for bob deint)

Information about the modeline I am using from XFree log:

(**) NVIDIA(0): Mode "720x576i": 13.9 MHz, 15.6 kHz, 50.0 Hz (I)

The modeline from XF86Config-4:

# 720x576i 50 Hz
Modeline "720x576i" 13.875 720 744 808 888 576 582 588 625 -HSync -VSync interlace

This is a 50 Hz interlaced modeline, so it should sync at 50 Hz which should be perfect for displaying PAL DVB because it is interlaced 25 FPS as shown by the following logs.

2006-01-15 08:56:21.795 detectInterlace(Detect Scan, Detect Scan, 25, 576) ->Interlaced Scan
2006-01-15 08:56:21.795 Interlaced: Interlaced Scan video_height: 576 fps: 25

I wondered if it was an issue because the modeline is interlaced, so I changed it to a non interlaced version as follows:

(**) NVIDIA(0): Mode "720x576p": 27.8 MHz, 31.2 kHz, 50.0 Hz
(II) NVIDIA(0): Setting mode "720x576p"

Modeline "720x576p" 27.75 720 744 808 888 576 582 588 625 -HSync -VSync

The error message about the video sync method went away, but the problem with the jerkiness still occurs after resuming from a pause. The "Video is n frames ahead of audio , dropping frame" messages still appear.

Any Ideas?
Greg Frost
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lists at ebourne

Jan 15, 2006, 6:18 AM

Post #7 of 11 (4377 views)
Permalink

Re: Problems with Bob Playback [In reply to]

On Sat, 14 Jan 2006 21:12:05 -0500, Michael T. Dean wrote:
> Martin Ebourne wrote:
>> Anything other than timestretch 1.0 works great, just at 1.0 it is
>> broken.
>>
> If using timestretch, bob deinterlacing is disabled, so that would explain
> why you don't see the problem with timestretch. :)

Yes, that is certainly implicated. But then something else is still going
on because with bob on and timestretch other than 1.0 the picture is
clearly being deinterlaced somehow - with bob off completely (from the
settings page) scrolling text has a comb effect at any timestretch, but
with bob on and timestretch in action there is no comb.

Actually, looking at the picture some more I think I can see what's
happening. With bob on and timestretch active the vertical resolution
appears to be halved, so I guess it's doing one-field deinterlacing
instead. That would explain the lack of shake.

Cheers,

Martin.

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danielk at cuymedia

Jan 15, 2006, 11:01 AM

Post #8 of 11 (4362 views)
Permalink

Re: Problems with Bob Playback [In reply to]

On Sun, 2006-01-15 at 14:18 +0000, Martin Ebourne wrote:
> On Sat, 14 Jan 2006 21:12:05 -0500, Michael T. Dean wrote:
> Actually, looking at the picture some more I think I can see what's
> happening. With bob on and timestretch active the vertical resolution
> appears to be halved, so I guess it's doing one-field deinterlacing
> instead. That would explain the lack of shake.

The result of using bob-deinterlacing with an interlaced display is
undefined. If you search the archives you will find that this has
been discussed before. If you are using an interlaced display and
need deinterlacing for some reason, then you should use some other
deinterlacer.

-- Daniel

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mtdean at thirdcontact

Jan 15, 2006, 12:57 PM

Post #9 of 11 (4359 views)
Permalink

Re: Problems with Bob Playback [In reply to]

Martin Ebourne wrote:
> On Sat, 14 Jan 2006 21:12:05 -0500, Michael T. Dean wrote:
>
>> Martin Ebourne wrote:
>>
>>> Anything other than timestretch 1.0 works great, just at 1.0 it is
>>> broken.
>>>
>> If using timestretch, bob deinterlacing is disabled, so that would explain
>> why you don't see the problem with timestretch. :)
>>
> Yes, that is certainly implicated. But then something else is still going
> on because with bob on and timestretch other than 1.0 the picture is
> clearly being deinterlaced somehow - with bob off completely (from the
> settings page) scrolling text has a comb effect at any timestretch, but
> with bob on and timestretch in action there is no comb.
>
> Actually, looking at the picture some more I think I can see what's
> happening. With bob on and timestretch active the vertical resolution
> appears to be halved, so I guess it's doing one-field deinterlacing
> instead. That would explain the lack of shake.
>
Yes. If you have enabled bob deinterlacing, you've told Myth that you
want deinterlacing, however bob only works at certain multiples of the
frame rate, so Myth falls back to one-field deint when you turn on
timestretch.

http://cvs.mythtv.org/trac/changeset/6723

Mike
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kcodyjr at verizon

Jan 15, 2006, 3:01 PM

Post #10 of 11 (4362 views)
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Re: Problems with Bob Playback [In reply to]

I'm still experimenting with this, so YMMV, but...

1.) If you're outputting to an interlaced mode, you shouldn't be doing
-anything- to the signal: match the monitor resolution to the capture
resolution, do not deinterlace by any means, and more importantly:

2.) Make sure your vertical refresh is synced to the source stream.
You're in PAL, so you need a 50Hz refresh rate - no getting around it.

With this approach, you shouldn't see any motion or scaling artifacts at
all. You will probably see the spaces between lines at 720x576, and in
an interlaced mode you'll definitely see the odd line phosphors fade
before the even lines are drawn, resulting in a twitchy picture.
Televisions have much slower phosphors.

Alternatively, you can process the signal to improve visible image
quality. YMMV, but try the following (only applies to CRT via VGA/DVI):

1.) Set your display to double the capture resolution, both directions.
2.) Use linear or kernel deinterlacing and progressive output.
3.) Set the vertical refresh to an even multiple of the source rate -
for PAL, any multiple of 25 from 75Hz up will do. NTSC will want 120Hz
if possible, 90Hz if not.

Allowing a noneven multiple refresh rate guarantees motion jitter. This
is one place where NTSC is actually more useful than PAL, for there is
no practical refresh rate that can be divided both by 25Hz (video) and
24Hz (film). 120Hz, however, divides cleanly by both 24 and 30.

IMO it's better for NTSC users to pick 90Hz at 2x resolution over 120Hz
at only 480 output lines; I can still see the spaces between lines even
in progressive mode regardless of refresh rate. Older monitors, and more
expensive recent monitors, might not have this problem.

Michael T. Dean wrote:

>Martin Ebourne wrote:
>
>
>>On Sat, 14 Jan 2006 21:12:05 -0500, Michael T. Dean wrote:
>>
>>
>>
>>>Martin Ebourne wrote:
>>>
>>>
>>>
>>>>Anything other than timestretch 1.0 works great, just at 1.0 it is
>>>>broken.
>>>>
>>>>
>>>>
>>>If using timestretch, bob deinterlacing is disabled, so that would explain
>>>why you don't see the problem with timestretch. :)
>>>
>>>
>>>
>>Yes, that is certainly implicated. But then something else is still going
>>on because with bob on and timestretch other than 1.0 the picture is
>>clearly being deinterlaced somehow - with bob off completely (from the
>>settings page) scrolling text has a comb effect at any timestretch, but
>>with bob on and timestretch in action there is no comb.
>>
>>Actually, looking at the picture some more I think I can see what's
>>happening. With bob on and timestretch active the vertical resolution
>>appears to be halved, so I guess it's doing one-field deinterlacing
>>instead. That would explain the lack of shake.
>>
>>
>>
>Yes. If you have enabled bob deinterlacing, you've told Myth that you
>want deinterlacing, however bob only works at certain multiples of the
>frame rate, so Myth falls back to one-field deint when you turn on
>timestretch.
>
>http://cvs.mythtv.org/trac/changeset/6723
>
>Mike
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>
>
>
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lists at ebourne

Jan 15, 2006, 4:24 PM

Post #11 of 11 (4352 views)
Permalink

Re: Problems with Bob Playback [In reply to]

On Sun, 15 Jan 2006 14:01:38 -0500, Daniel Kristjansson wrote:
> The result of using bob-deinterlacing with an interlaced display is
> undefined. If you search the archives you will find that this has been
> discussed before. If you are using an interlaced display and need
> deinterlacing for some reason, then you should use some other
> deinterlacer.

True indeed, but while I can see many people do seem to use deinterlacing
with an interlaced TV I'm glad to say I'm not that daft. :)

What I have had until now is a normal TV for which I didn't use any
deinterlacing, and therefore worked fine making sure there was no scaling.
I've just switched to a new LCD which does need deinterlacing. I wouldn't
have posted to the list if I hadn't seen the current thread which sounded
very similar.

I've fixed my problems now though. I enabled the 'Field' debugging for Bob
in videoout_xv.cpp to see what was going on and found that some of the
values were wrong (especially the source ones). I tracked it down to some
overscan settings still set from the TV which I'd forgotten about. I
reset those and now I've got excellent Bob playback and am very happy.

There do seem to be some bugs here though:

1. With the overscan settings bob was getting the calculations wrong. Up
close at the tv with horizontal lines in the picture it was clear the top
& bottom frames were being displayed several lines apart, rather than just
one.

2. The timestretch is being disabled based on playback speed. This is
wrong, it should be done based on source and video vertical frame rates.
Unfortunately it is not always possible to get 50Hz display rate on
modern screens. Most LCDs only do 60Hz (or maybe 75Hz) through the VGA or
DVI ports. Fine for NTSC, but in PAL land we have to live with displaying
50Hz material on a 60Hz screen. In this case timestretch at 1.2x should be
the correct display rate and should therefore use bob. Even if I was
displaying on 50Hz I've also got some NTSC DVDs so it still matters.

3. Even if timestretch is in use, bob should only be disabled for
playback rate > display rate. When that is the case bob clearly doesn't
work and gives really jerky movement. If playback rate < display rate (ie.
normally when timestretch < 1) the bob does work very effectively still.
It always seems to produce better results than onefield. eg. 50Hz playback
on 60Hz is entirely watchable - 95% smooth.

I'll most likely code up 2 & 3 and submit a patch when I get chance.

Cheers,

Martin.

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