Conversion artefact full HD TS files

[pasja]

Not much TV stations are sending on full HD (1920*1080).
Recording with a satellite receiver produces a TS file. A recorded full HD TS file correctly plays with a mediaplayer or PC (vlc, MPC-HC or Kodi).
However, when I convert the TS file into another format an artefact arises in the first beginning (~ 1 sec). It shows a block pattern before correct playing starts.
This artefact arises independent of the conversion programme used (Freemake, Bigasoft or Handbrake).
Any solution possible?

[pasja]

Instead of block pattern, I may better say: strong pixelation.

[LigH.de]

Most probably, the recording of the TransportStream does not start at the beginning of a GOP, so that some decoders start to decode inter frames which have no intra reference (imagine an expression like "two more", but you don't know "two more than ... how many at first?"). There may be other decoders which skip decoding until a GOP starts; or you have to pre-cut your recording a bit and remove the incomplete first GOP with tools which can handle that issue in TransportStreams specifically.

[pasja]

Most probably, the recording of the TransportStream does not start at the beginning of a GOP, so that some decoders start to decode inter frames which have no intra reference (imagine an expression like "two more", but you don't know "two more than ... how many at first?"). There may be other decoders which skip decoding until a GOP starts; or you have to pre-cut your recording a bit and remove the incomplete first GOP with tools which can handle that issue in TransportStreams specifically.

Thanks for your reaction. Although I do not know what a GOP is (I will search for that later) I believe your are right. I did some experimentation and I indeed found that if the conversion programme allows cutting, that cutting of -say- the first sec before the conversion solves the problem. It is better to miss the first sec. than to start with an artefact. It means that the artefact is already in the TS stream. I will notify TS Doctor. Thanks for the reaction.

[LigH.de]

I do not have much practical experience, but AFAIR, TS Doctor is among the recommended tools for pre-cleaning DVB recordings (which includes cutting the possibly incomplete start).

[pasja]

I do not have much practical experience, but AFAIR, TS Doctor is among the recommended tools for pre-cleaning DVB recordings (which includes cutting the possibly incomplete start).

I noticed the artefact after cutting with TS Doctor. I always cut at IF points. And I did not notice the effect with lower resolution TS (lower than 1920*1080).
I put my observation (and your reaction) on their Forum and awaits their reaction.

[sneaker]

Is the lower resolution using a different video format? Often HD is H.264 while SD is MPEG-2. The programs might treat those differently.

[LigH.de]

I would even have guessed that interlaced AVC was treated wrong; some software mistreated interlaced AVC in TS. But that's bold guessing.

Not to forget that interlacing in AVC can be PAFF as well as MBAFF. Hardware encoders will probably produce PAFF.

Blu-ray compatible encoding will require interlacing for some combinations of 1080 resolution and frame rates. I am not sure if DVB is just as strict.

[pasja]

First I am not a specialist, so many concepts (GOP, interlaced, PAFF etc) are not familiar for me and not understood.
Everything goes well with German broadcasts (cutting with TS Doctor followed by conversion).
MediaInfo says for some German TS files for instance: MPEG-TS; First Video stream 11.2 Mb/s; 1280*720 at 50 fps; AVC (High@L4) (CABAC/6 Ref Frames)
but for others: MPEG-4 (Base Media); First Video stream 5005 kbs; 1280*720 at 50 fps, AVC (Main@L3.1) (1Ref Frames).

Pixelation at the first sec are with BBC and with Brava. (cutting with TS Doctor no problem followed by conversion pixelation at the onset).
MediaInfo says for BBC TS and for Brava TS: MPEG-TS; First Video stream 6715 kbs; 1920*1080 at 25 fps; AVC (Component)(High@L4)(CABAC/4 Ref Frames).

In a reaction of Cypherus (TS Doctor) the different behavior is attributed to H264 (BBC) and MPEG-2 (others) and that H264 has no GOP.

My problem is solved by cutting the first sec during conversion. The detailed info of MediaInfo and the details of the discussion are not well understood by me.

[LigH.de]

First I am not a specialist, so many concepts (GOP, interlaced, PAFF etc) are not familiar for me and not understood.

Group of pictures (better diagram in Inter frame or in the German Wikipedia: Bildergruppe) is a basic concept necessary to understand most of the modern video codecs. Especially the fact that most frame content depends on previously decoded frame content because only a difference to a previous frame is stored (in case of B frames, even the minimum of differences to two frames, displayed either in the past or in the future of the currently decoded frame).

There are small structure differences between "open" and "closed" GOPs: The encoding of an open GOP is slightly more efficient, but relies on a previously decoded GOP for the first few dependent frames. A closed GOP, on the other hand, is mostly independent from a previous GOP, but independence (and thus better decodability from anywhere in the middle of the video) costs a bit additional bitrate.

MediaInfo says for some German TS files for instance: MPEG-TS; First Video stream 11.2 Mb/s; 1280*720 at 50 fps; AVC (High@L4) (CABAC/6 Ref Frames)
but for others: MPEG-4 (Base Media); First Video stream 5005 kbs; 1280*720 at 50 fps, AVC (Main@L3.1) (1Ref Frames).

That sounds like some of your files are indeed TransportStreams, but others are in an MP4 container instead. For a more certain comparison, you should possibly post some verbose MediaInfo analysis reports (for the CLI version of MediaInfo, use the parameter "-f"; for the GUI version, enable "Advanced mode" in the "Debug" menu, and export a "text" format report).

and that H264 has no GOP.

Surely not "no GOP"; but maybe "no closed GOP".

The detailed info of MediaInfo and the details of the discussion are not well understood by me.

Show us the detailed reports (due to the length, rather attached or on pastebin's). Some of us know well which details to look for.