[Ffmpeg-devel] [Ffmpeg-devel-old] Question about interlaced_frame and top_field_first

Luca Abeni lucabe72
Fri Jan 27 17:04:14 CET 2006

Hi all,

while working on the new video4linux2 input, I tried to design it to
properly set the interlaced_frame and top_field_first fields... How can
I obtain such result?

If I understand well, interlaced_frame and top_field_first are set by
the video codec (CODEC_ID_RAWVIDEO): how can the input format tell the
video codec how to set such fields? I immagine I can modify
raw_init_decoder() to properly set interlaced_frame and top_field_first
in priv_data.pic... But how can it decide if frames will be interlaced
or not? Should I add a new field to AVCodecContext? Or there is a simple
way that I am not seeing?

I am also wondering how such fields are used in libavcodec /
I mean: if I capture video from a bttv card, the video is interlaced but
interlaced_frame is never set (and maybe top_field_first has the wrong
value). What happens if I encode the video (for example using mpeg* with
Which kind of problems will I see?

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