BBC HD Frame rate query (1 Viewer)

[porky996t]

Hi Guys,

I'm being a bit picky trying to resolved a dropped frames problem (well, not really a problem, I'm just being a bit anal - dropping about 30 frames in 20,000) Whilst displaying the "shift & 1" screen and watching BBC HD I noticed that the frame rate was up and down like a brides nightie. It varies between 24.9999, 49.9999, 24.2, 24.3,24.6 I then tried Channel 4 HD and that too varies between 21, 22, 23, 24.999, 32, 34, 35 and up to 49.9999

Can anybody explain what is happening?

I am using DVB-T2, although not tried DVB-S2 to see if it changes anything.

 

[jameson_uk]

AIUI this is just what the broadcast stream is reporting as the frame rate. If you are seeing any issues (I was getting annoying lip sync issues on 4HD when they keep reporting output as 24fps when using MPAR) then try the latest TSReader (https://forum.team-mediaportal.com/threads/experimental-tsreader-development.102693/) as that tries to get the fps from the video rather than what is reported in the transport stream

 

[Owlsroost]

In addition to what jameson_uk has said, UK Freeview HD uses dynamic field/frame encoding i.e. the FPS flips between 25 and 50 depending on picture content (FPS after deinterlacing, which is what dshowhelper sees).

The only H.264 decoder I've found that can handle this properly is LAV Video Decoder, with the 'Aggressive Deinterlacing' box ticked in it's settings - otherwise you'll sometimes get a burst of stuttering and dropped/repeated frames whenever the video transitions between 25 & 50 fps.

In the render stats screen, 'Act FPS' (& the red line) is real time actual rendering rate to the screen, 'Rptd FPS' is what the source/splitter filter (e.g. TsReader.ax for TV) thinks it is, and 'Detd FPS' is what dshowhelper calculates from the video stream timestamps in real time. If the system is not dropping frames then 'Act FPS' and 'Detd FPS' should be the same, but 'Rptd FPS' can be different e.g. Rptd FPS = 25 and Detd FPS = 50

Note that 'Act FPS' and 'Detd FPS' are smoothed/averaged values, but the red line is not smoothed so dropped/repeated frames show up as glitches.

 

[porky996t]

@jameson_uk @Owlsroost

Just a quick update and message of thanks.

First I tried using LAV with Aggressive Deinterlacing and I was getting more dropped frames than with the MS Codec. I then tried the "non stop mod70" TS Reader and this reduced the dropped frames from about 130 per 20,000 to 3 per 30,000 which ain't bad at all.

I was beginning to doubt all sorts of things such as network speed, or TV Cards or even the new graphics card I put in this lounge PC the other week.

Thanks again, HD is now great! If you were both local I'd get you a pint.

EDIT: I have also put this TS Reader on both my Zotac Zbox ID41 clients and it has certainly improved the 'watchability' of the HD channels. Whilst they performed well, occaisional dropped frames were a pain. I'm now getting about 12 - 14 dropped frames per 30,000 and this is with the BBC HD channel that is just previewing HD stuff with an extremely variable FPS