Occasional stuttering in MKV encoded AVC video

[svenssonsven8]

Hi all,

I need some help in understanding why my video encoded to mkv is sometimes stuttering during playback. The stuttering is most prominent during small movements, so my first thought was that QTGMC setting was too forgiving (using 'Slower'). Thus I encoded a segment of the file in three different speeds: 'Slower', 'Very Slow' and 'Placebo'. The resulting encodings are attached. The stuttering can be noticed between 8 and 11 seconds into the video, while the cars are moving. The whole video playback appears not to be smooth.

However, I am unable to see any noticable difference regarding the stuttering between the three QTGMC settings above. Currently, I am suspecting that there is an issue with the indexer I am using (DGDecodeNV), but I am far from sure.

I've also attached the sample AVS script used to encode the three sample files attached. Are there any obvious issues with it, or any improvement suggestions?

Thank you in advance.

Kind Regards,
Veroslav

Input AVC file:

Original input file:

General
ID                                       : 1062 (0x426)
Complete name                            : C:\file.ts
Format                                   : MPEG-TS
File size                                : 4.05 GiB
Duration                                 : 1h 57mn
Overall bit rate mode                    : Variable
Overall bit rate                         : 4 927 Kbps

Video
ID                                       : 160 (0xA0)
Menu ID                                  : 30001 (0x7531)
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High@L4
Format settings, CABAC                   : Yes
Format settings, ReFrames                : 4 frames
Codec ID                                 : 27
Duration                                 : 1h 57mn
Bit rate                                 : 4 296 Kbps
Width                                    : 1 920 pixels
Height                                   : 1 080 pixels
Display aspect ratio                     : 16:9
Frame rate                               : 25.000 fps
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : MBAFF
Scan type, store method                  : Separated fields
Scan order                               : Top Field First
Bits/(Pixel*Frame)                       : 0.083
Stream size                              : 3.53 GiB (87%)
Color range                              : Limited
Color primaries                          : BT.709
Transfer characteristics                 : BT.709
Matrix coefficients                      : BT.709

Audio #1
ID                                       : 80 (0x50)
Menu ID                                  : 30001 (0x7531)
Format                                   : MPEG Audio
Format version                           : Version 1
Format profile                           : Layer 2
Codec ID                                 : 4
Duration                                 : 1h 57mn
Bit rate mode                            : Constant
Bit rate                                 : 192 Kbps
Channel(s)                               : 2 channels
Sampling rate                            : 48.0 KHz
Compression mode                         : Lossy
Delay relative to video                  : 20ms
Stream size                              : 162 MiB (4%)
Language                                 : Spanish
Language, more info                      : Clean effects

Audio #2
ID                                       : 81 (0x51)
Menu ID                                  : 30001 (0x7531)
Format                                   : MPEG Audio
Format version                           : Version 1
Format profile                           : Layer 2
Codec ID                                 : 4
Duration                                 : 1h 57mn
Bit rate mode                            : Constant
Bit rate                                 : 192 Kbps
Channel(s)                               : 2 channels
Sampling rate                            : 48.0 KHz
Compression mode                         : Lossy
Delay relative to video                  : 44ms
Stream size                              : 162 MiB (4%)
Language                                 : qaa
Language, more info                      : Clean effects

AVS script:

# Set DAR in encoder to 64 : 45. The following line is for automatic signalling
global MeGUI_darx = 64
global MeGUI_dary = 45

LoadPlugin("C:\megui\tools\dgindexnv\DGDecodeNV.dll")
LoadPlugin("C:\megui\tools\avisynth_plugin\UnDot.dll")

ms = DGSource("C:\file.dgi",fieldop=0)
ms = ms.Trim(8293,8793)

ms = ms.crop(286, 26, -282, -6)
ms = ms.Undot()
ms = ms.Spline36Resize(960,ms.height)
ms = QTGMC(ms, Preset="Placebo", Sharpness=0.8)
ms = ms.Spline36Resize(ms.width,720)

return ms

x264 command line:

C:\megui\tools\x264\x264.exe --level 4.1 --preset veryslow --cabac --ref 5 --deblock -3:-3 --partitions all --me umh --subme 8 --psy-rd 1.00:0.00 --merange 24 --trellis 2 --8x8dct --cqm flat --deadzone-inter 21 --deadzone-intra 11 --chroma-qp-offset 0 --threads 12 --lookahead-threads 2 --no-dct-decimate --bframes 6 --b-pyramid normal --b-adapt 2 --b-bias 0 --direct auto --weightp 2 --keyint 500 --min-keyint 50 --scenecut 40 --rc-lookahead 40 --crf 20.0 --qcomp 0.60 --qpmin 10 --qpmax 51 --qpstep 4 --stitchable --ipratio 1.40 --aq-mode 1 --aq-strength 1.00 --sar 16:15 --output C:\output.264 C:\script.avs

[jagabo]

I only downloaded the "slower" video but I don't see any problems here. 50 fps video does judder a bit on a 60 Hz monitor. However, changing the frame rate to 60 fps showed perfectly smooth video. Stepping through the video frame by frame there are a few places where one car moves but another doesn't. But I doubt that's QTGMC's problem. It's more likely motion artifacts in the original video or the final encoding.

[svenssonsven8]

Thank you for your reply, jagabo.

I am playing the video on my media player at 50 fps (an option I set in the player). I admit that it can be hard to notice the stuttering. I would also like to know whether I need to use AssumeTFF(), as the clip is "Top Field First", according to the media info?

[jagabo]

I haven't used DgDecodeNV but Donald Graft's MPEG 2 decoder (Mpeg2Source) sets AviSynth's field order. So I would guess DgDecodeNV does too. If the field order was backward you would see very obvious two-steps-forward-one-step-back motion. That's not the problem here.

Try using a simple Bob() instead of QTGMC() and see if the motion looks any smoother.

[svenssonsven8]

Thank you for helping me jagabo, much appreciated!

Just tried with:

Yadif(clip, Mode=1, Order=1)

but no difference

[svenssonsven8]

Actually, looking a bit closer, it appears to me that it is not the motion specifically that is stuttering, but the whole picture itself.

[jagabo]

In addition to the helicopter motion the camera might be panning with a little jerkiness.