[Libav-user] Scale filter converting to grayscale

[Philippe Gorley]

Hi,

I'm having trouble getting filters to work correctly. It creates dummy 
YUV frames, scales them using libavfilter, and saves the raw data to 
disk (heavily based on filtering_video.c). The end goal is to use 
libavfilter instead of implementing such things ourselves.

It segfaults when writing the frame. I'm expecting a yuv420p frame, but 
the filtered frame is in grayscale (AV_PIX_FMT_GRAY8), even though I 
specify yuv420p in the filter string (scale=w=200:h=100:dst_format=0).

Here is the code: https://pastebin.com/rNegZcng
I'm on FFmpeg master (commit cae6f806a6367c7760ab6ed059d343d4a8eebd56).

And here are the logs I'm getting:
detected 4 logical cores
[in @ 0x1e41200] Setting 'video_size' to value '320x240'
[in @ 0x1e41200] Setting 'pix_fmt' to value '0'
[in @ 0x1e41200] Setting 'time_base' to value '1/1'
[in @ 0x1e41200] Setting 'pixel_aspect' to value '1/1'
[in @ 0x1e41200] w:320 h:240 pixfmt:yuv420p tb:1/1 fr:0/1 sar:1/1 sws_param:
[Parsed_scale_0 @ 0x1e42280] Setting 'w' to value '200'
[Parsed_scale_0 @ 0x1e42280] Setting 'h' to value '100'
[Parsed_scale_0 @ 0x1e42280] Setting 'dst_format' to value '0'
[Parsed_scale_0 @ 0x1e42280] w:200 h:100 flags:'bilinear' interl:0
[AVFilterGraph @ 0x1e407c0] query_formats: 3 queried, 2 merged, 0 
already done, 0 delayed
[Parsed_scale_0 @ 0x1e42280] w:320 h:240 fmt:yuv420p sar:1/1 -> w:200 
h:100 fmt:gray sar:2/3 flags:0x2
[Parsed_scale_0 @ 0x1e42280] w:320 h:240 fmt:yuv420p sar:0/1 -> w:200 
h:100 fmt:gray sar:0/1 flags:0x2
[swscaler @ 0x1e42f80] bad dst image pointers
Frame scaled from 320x240 to 200x100
Segmentation fault

Backtrace:
#0  __mempcpy_sse2 () at ../sysdeps/x86_64/memcpy.S:196
#1  0x00007ffff7364242 in _IO_new_file_xsputn (f=0x635430, data=0x0, 
n=0x64) at fileops.c:1319
#2  0x00007ffff73597bb in __GI__IO_fwrite (buf=0x0, size=0x64, 
count=0x1, fp=0x635430) at iofwrite.c:39
#3  0x000000000040114b in save_yuv_frame (frame=0x604040, 
frame_number=0x0) at video_filter.c:52
#4  0x0000000000401a4f in main (argc=0x1, argv=0x7fffffffda48) at 
video_filter.c:203

Any tips on what I'm doing wrong and why libavfilter is converting my 
frame to AV_PIX_FMT_GRAY8?

Cheers,

-- 
Philippe Gorley
Free Software Consultant | Montréal, Qc
Savoir-faire Linux

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