[vlc-devel] Transcoding and wrong aspect calculation

Bjørn Olav Ruud bjorn.ruud at gmail.com
Fri Jan 19 14:24:14 CET 2007

Some TS streams get wrong aspect upon playback after being transcoded.
I use this command line to receive a multicast stream, transcode it,
and output a new multicast stream:

vlc \
--color \
--extraintf logger \
--logfile test-server.log \
-vvv \
--ttl 12 \
--udp-caching 10000 \
--sout '#transcode{vcodec=mp4v,vb=2000,deinterlace}:std{access=udp,mux=ts,url=}'

Server side I have these messages regarding aspect ratio:

libmpeg2 decoder debug: 720x576 (display 720,576), aspect 768000, sar
64:45, 25.000 fps
stream_out_transcode private debug: decoder aspect is 768000:432000
stream_out_transcode private debug: source pixel aspect is 1.422222:1
stream_out_transcode private debug: scaled pixel aspect is 1.419753:1
stream_out_transcode private debug: source 720x576, crop 720x576,
destination 720x576, padding 720x576
stream_out_transcode private debug: encoder aspect is 766667:432000

Upon playback VLC reports this:

main debug: picture in 720x576 (0,0,720x576), chroma I420, ar 425:128, sar 85:32
main debug: picture user 720x576 (0,0,720x576), chroma I420, ar
425:128, sar 85:32
main debug: picture out 720x576 (0,0,720x576), chroma I420, ar
425:128, sar 85:32

Since I haven't specified any scaling parameters, shouldn't the scaled
pixel aspect be the same as the source pixel aspect? If not, might the
problem lie with the TS muxer and not with transcode.c?

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