[FFmpeg-user] Errors in swscaler or broken video

[WR]

Am 08.05.2021 um 10:58 schrieb WR:
> Hello community,
> 
> since some days I experience errormessages in ffplay:
> (ffplay version 4.2.4-1ubuntu0.1 )
> 
> [swscaler @ 0x55c6a680c880] 82x0 -> 82x0 is invalid scaling dimension
> Cannot initialize the conversion context
> [swscaler @ 0x55c6a680c880] 82x0 -> 82x0 is invalid scaling dimension
> Cannot initialize the conversion context
> [swscaler @ 0x55c6a680c880] 82x0 -> 82x0 is invalid scaling dimension
> Cannot initialize the conversion context
> [swscaler @ 0x55c6a680c880] 82x0 -> 82x0 is invalid scaling dimension
> Cannot initialize the conversion context
> [swscaler @ 0x55c6a680c880] 82x0 -> 82x0 is invalid scaling dimension
> Cannot initialize the conversion context
> [swscaler @ 0x55c6a680c880] 82x0 -> 82x0 is invalid scaling dimension
> Cannot initialize the conversion context
> [swscaler @ 0x55c6a680c880] 291x0 -> 291x0 is invalid scaling dimension
> Cannot initialize the conversion context
> [swscaler @ 0x55c6a680c880] 291x0 -> 291x0 is invalid scaling dimension
> Cannot initialize the conversion context
> [swscaler @ 0x55c6a680c880] 291x0 -> 291x0 is invalid scaling dimension
> Cannot initialize the conversion context
> [swscaler @ 0x55c6a680c880] 291x0 -> 291x0 is invalid scaling dimension
> Cannot initialize the conversion context
> [swscaler @ 0x55c6a680c880] 291x0 -> 291x0 is invalid scaling dimension
> Cannot initialize the conversion context
> [swscaler @ 0x55c6a680c880] 291x0 -> 291x0 is invalid scaling dimension
> Cannot initialize the conversion context
> [swscaler @ 0x55c6a680c880] 291x0 -> 291x0 is invalid scaling dimension
> Cannot initialize the conversion context
> [swscaler @ 0x55c6a680c880] 291x0 -> 291x0 is invalid scaling dimension
> Cannot initialize the conversion context
> 
> The messages arise in chunks and while they arise video output is black. 
> between the chunks, the video runs fine.
> 
> It only happens, when I play a video, which I edited before with 
> ffmpeg's crop-filter :
> -c:v libx264 -preset medium  -filter:v crop=iw-0-0:ih-72-74:0:72
> 
> The source video comes from a DVD (from what I created a concat-file 
> with dvd2concat-script from ffmpeg-sources)
> 
> I do that to cut the black stripes on the top and at the bottom.
> When I don't use the crop filter, the result video runs fine in ffplay.
> 
> The cropped video (which produces the error messages) runs fine in other 
> players (vlc, parole). I also (for test) took it as input for another 
> transcoding in ffmpeg -> no errors while processing (but again errors 
> while playing this result)
> 
> So my question is: can I be sure, that the cropped videofile is without 
> scaling faults and only the ffplay has a problem while playing? Or is 
> the cropped video really erroneous because the crop filter makes 
> mistakes and all other players are a bit more "scaling problems friendly".
> 
> I think this appeared since one of the last ubuntu updates, I can't 
> remember such an effect in former times, but I use the crop filter since 
> a long time now.
> 
> (And another strange effect in the last days is, that video playback 
> runs in double speed for some seconds, when I switch the audio-channels 
> with key A. I've never seen this before.)
> 
> Thank you, RockfordC64
> 

Hello Again,

I think I've got it. The problem is really a playback-problem. And it 
has nothing to do with a software-update.
The reason is, that I learnt, how to save the subtitles from the DVD to 
my videofile. And the combination of subtitlestreams and cropped video 
stream is the reason of the swscaler-errors.
I believe that after cropping the video, and leaving the subtitles, as 
they are, the bitmaps of the subtitles are to large to fit on the video.
When I switch off subtitles in ffplay, errors and black screen gaps 
don't occure.
Maybe, there is a way, to scale the subtitles in that way, that they 
would fit the videos size.
Please correct me, if I'm wrong.

Thank you, RockfordC64


-- 
May the source be with you