Artefacts at onset full HD TS files

Begonnen von Oldman13, August 31, 2017, 14:47:53

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Oldman13

There are not much TV stations which send full HD (1920*1080).
For me interesting stations in this respect are BBC and Brava. Working with TS Doctor seems ok. For cutting with TS Doctor I always use IF points. Resulting TS files play correctly on PC and mediaplayer.
However, artefacts become visible when converting these full HD TS files to another format. Strong pixelation or even other effects take place with conversion in the beginning of the resulting file (~ 1 sec). After ~ 1 sec the converted file plays without further problems. The effect takes place independent of the conversion programme used (Freemake, Bigasoft, Handbrake). I am now convinced that the artefact is already in the TS file, although not noticible when the TS file is played.
With TS Doctor and with Freemake it is possible to see individual frames (in their respective cutting sections). There, a difference becomes visible.
For BBC records both TS Doctor and Freemake show these artefacts in the images. For Brava, only Freemake shows pixelation in the first frames.

I did find some solution to the problem. With Freemake and Bigasoft, when cutting the first second it yields a converted file without artifacts. It is better to miss the first second than to start a movie with pixelation.

Oldman13

Since at first I thought that the artefact was conversion related, I put the question already on another forum. From this forum came a reaction from Light.de, which seems to me relevant although I am not familiar with the details. The reaction reads:

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.


Cypheros

OK, that is a difficult problem, because H264 (used by BBC for full HD) has no GOP! GOP applies only for MPEG2.

H264 is more difficult than MPEG2. TS-Doctor tries to remove disturbing frames but some decoders doesn't handle that correctly. As TS-Doctor creates no frames but only removes them, it's not possible to make it work for any player/transcoder without artefacts at the cutting points, if that tools process frames blindly.


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