[Ffmpeg-devel] Re: Bethsoft VID demuxer and decoder

Michael Niedermayer michaelni
Sat Apr 7 17:26:02 CEST 2007


On Sat, Apr 07, 2007 at 07:23:13AM -0700, Nicholas T wrote:
> >>    vid->frame.data[0] = NULL;
> >this was wrong
> I think other codecs had it to ensure that the codec close function
> wouldn't try to free a buffer with no data in it. Just out of
> curiosity, why is this wrong? because frame data is not initialized
> yet, or it is just unneeded

it either does nothing or hides a bug

> >clicking on the window is supposed to seek not pause
> okay, so, what do I do, or should I ignore this...bethsoftvid
> obviously isn't the greatest format for seeking, as the block sizes
> aren't known...

i dont think seeking is trivially possible in this format so just
forget seeking

> >and its of course not possible that the end could have been reached
> >if remaining>0 your checks are much more complex than needed
> >one thing which you should check though is that the initial pointer
> >before the loop is entered is valid (VIDEO_OFFSET_DIFFERENCE_FRAME_BLOCK
> >frame can move that to pretty much arbitrary positions)
> Okay, I did this in a pretty simple way, hopefully it's valid.
>            yoffset = bytestream_get_le16(&buf);
>            if(yoffset > avctx->height) { return -1; }

should be >=

>            destination += vid->frame.linesize[0] * yoffset;
> >i know that, my question was if such 0 index actually occurs
> >from a hex dump it appears it does.
> >wrong, these are not initalized before (re)get_buffer()
> sorry. I can assume linesize doesn't change though, right?

well other codecs assume that too so its ok ...

ill review the patch in a moment ...

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Breaking DRM is a little like attempting to break through a door even
though the window is wide open and the only thing in the house is a bunch
of things you dont want and which you would get tomorrow for free anyway
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