[Libav-user] avfilter generates garbage after 3f9137c without setting AVFrame::pts to AV_NOPTS_VALUE

[Max Weber]

Commit 3f9137c 
<https://github.com/FFmpeg/FFmpeg/commit/3f9137c57d2344d7613f134128235c18edcede95>changed 
how avfilter behaved in my application and I was wondering if it is a 
FFmpeg bug, my bug, or intended behavior?

My application reads in media with avfilter/avcodec, resizes it with 
swscale, applies an overlay with avfilter, swscales it again, then 
encodes it with libjpeg-turbo. If I don't set AVFrame::pts to 
AV_NOPTS_VALUE before giving it to avfilter, I get a blank frame with 
some garbage at the bottom 
<https://abex.sauville.org/ffmpeg_garbage/garbage%20at%20bottom.jpg>. 
Additionally this only happens with some PNG inputs 
<https://abex.sauville.org/ffmpeg_garbage/rawpng.png>(afaik, haven't 
tried many formats). This does not happen with h264 in a mp4, or with a 
PNG in a mp3 <https://abex.sauville.org/ffmpeg_garbage/png_in_mp3.mp3>. 
In this configuration only one frame goes through the filter before it 
is destroyed.

Relevant code in my application is here:
base.go 
<https://bitbucket.org/Abex/yumeko/src/3960c8e03f2e69a329b1074ba6bda7fb2b08c112/thumblink/mutators/thumbnailer/base.go?fileviewer=file-view-default#base.go-393>
format.h 
<https://bitbucket.org/Abex/yumeko/src/3960c8e03f2e69a329b1074ba6bda7fb2b08c112/ffmpeg/format.h?fileviewer=file-view-default>
format.go 
<https://bitbucket.org/Abex/yumeko/src/3960c8e03f2e69a329b1074ba6bda7fb2b08c112/ffmpeg/format.go?at=master&fileviewer=file-view-default>

Unfortunately this code does not lend itself to debugging very well, due 
to tight integration, lack of testing, and FFI borders, so if this does 
look like a bug, I can try to get a smaller repro if that would help.


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