Deinterlace?

terrypin wrote on 9/30/2015, 3:50 AM

I haven't used my Vimeo account a great deal so had not seen the following until today. I'd just uploaded a family video and noticed this message:

Help this video look its best by following these video file recommendations

One of the two recommendations was to increase bit rate (straightforward). The second was to deinterlace:

Should I deinterlace before I upload?

It's almost always a good idea. If you're outputting 1080i, deinterlace and resize to 1280×720 before you upload. If your final outcome is a progressive medium (web, HDTVs, Blu-Ray, etc.) you might want to deinterlace before you even start editing.

I'd appreciate thoughts from the experts on this please?

Here's an extract from MediaInfo:

Format: MPEG-4
Format profile: Base Media / Version 2
Codec ID: mp42
Overall bit rate mode: Variable
Overall bit rate: 8334 Kbps
Format: AVC
Format/Info: Advanced Video Codec
Format profile: High@L4
Format settings, CABAC: Yes
Format settings, ReFrames: 3 frames
Format settings, GOP: M=1, N=33
Codec ID: avc1
Codec ID/Info: Advanced Video Coding
Duration: 54mn 9s
Bit rate: 8 172 Kbps
Width: 1920 pixels
Height: 1080 pixels
Display aspect ratio: 16:9
Frame rate mode: Constant
Frame rate: 25.000 fps
Standard: PAL
Color space: YUV
Chroma subsampling: 4:2:0
Bit depth: 8 bits
Scan type: Interlaced
Scan order: Top Field First
Bits/(Pixel*Frame): 0.158
Stream size: 3.09 GiB (98%)
Color range: Limited
Color primaries: BT.709
Transfer characteristics: BT.709
Matrix coefficients: BT.709

--
Terry, East Grinstead, UK

Comments

johnebaker wrote on 9/30/2015, 4:39 AM

Hi Terry

The reason for the de-interlace is because LCD monitors are Progressive scan devices, as are LCD Tv's and as ou will have noticed they play interlaced video OK.

The real advantage in using a Progressive video is for mobile devices.

De-interlacing to Progressive does introduce a problem which can be very irritating to the viewer - where there is a panning shot or movement across the screen the image can apear to jerk.

I used to advise using the recommended settings from Youtube and Vimeo, however I have had issues with them - in particular Youtube.

I now use the following settings for the MainConcept codec - these were determined after many days testing analysing and playing on a multitude of devices from the web:

Setting	480p (720p)

Resolution	854 x 480 (1240 x 720)
Framerate	25 fps
AR	16:9
AVC Encoder	Auto
AVC Preset	High
Profile	High
Level	5
Performance	9
Frame type	Progressive
Slice count	1
Max GOP length	100
Max B frames	3
Adaptive B frames	checked
Mode	Variable bitrate
Bitrate	2570 (3800)
HSS bitrate	8000
CPB size	32000
Picture aspect ratio	16:9

I save these as presets for exporting for the web.

HTH

John EB

Scenestealer wrote on 9/30/2015, 9:59 AM

Hi Terry

I guess their suggestion to deinterlace to 720p is based on the fact that 1080i is only half the vertical resolution of 1080p so you might as well encode to 720p which would be the effective vertical resn. after deinterlacing anyway. This is because deinterlacing in its' simplist form just throws away every alternate line and duplicates the other one and this is why it creates a jerky pan as John has mentioned.

Their suggestion to deinterlace before editing is a new one but it is likely based on the fact that deinterlacing on the fly in your editing program uses extra resources during preview. I always uncheck the deinterlace setting in the Program settings when I have Progressive footage on the timeline and smoother preview is the result.

John - I presume you mean 1280 x 720 and not 1240 x 720?

Peter

terrypin wrote on 9/30/2015, 1:52 PM

John, Peter,

Thanks both. I'll experiment with those suggestions in mind.

--
Terry, East Grinstead, UK

johnebaker wrote on 9/30/2015, 2:46 PM

@Peter

. . . . I presume you mean 1280 x 720 and not 1240 x 720? . . .

You are correct - missed the typo !!!

. . . . I guess their suggestion to deinterlace to 720p is based on the fact that 1080i is only half the vertical resolution of 1080p so you might as well encode to 720p which would be the effective vertical resn. after deinterlacing anyway. . . .

The reason for reducing the resolution is due to bandwidth and datarate constraints with respect to the devices, in particular mobile devices, connection speeds when playing video from the Internet.

This is one of the problems I had with putting hires video on our website and the amount of time and testing to ensure a suitable format which would work on most devices. This included uploading not just mp4 but ogv and webm formats as well.

With current de-interlacers there is no loss of vertical resolution - most de-interlacers use a line by line a combination of:

Static combination - where there is no movement in the image between fields, then the static parts of the 2 fields are added together.
Motion adaptive deinterlacing - where there is movement in the image the de-interlacer interpolates the change of a moving object between the top field and bottom field of sequential frames to generate a line - this removes or smooths out the fact that one field was recorded after the other.

This is because interleaved PAL (NTSC) video at 25fps (30fps) contains 50 (60) fields per second - one field is half the vertical resolution - 2 interlaced fields give one full image so by combining fields as above you still end up with a framerate of 25fps (30fps) but progressive.

The jerkiness results from the direction of pan or movement, the motion adaptive de-interlacing has a larger difference in one direction compared to the other to interpolate correctly.

For example with my Top Field First (TFF) video the jerkiness is worse in a right to left pan then a left to right pan when converted to progressive.

HTH

John EB