[FFmpeg-devel] [RFC] seek when streamed

[Michael Niedermayer]

On Tue, Nov 13, 2007 at 12:31:55AM +0100, Baptiste Coudurier wrote:
> Hi,
> 
> Michael Niedermayer wrote:
> > On Sun, Oct 07, 2007 at 10:59:33PM +0200, Baptiste Coudurier wrote:
> > 
> >>Hi
> >>
> >>I noticed a weird behaviour (bug ?) when seeking is requested when file
> >>is streamed:
> >>
> >>in url_fseek:
> >>    } else if(s->is_streamed && !s->write_flag &&
> >>         offset1 >= 0 && offset1 < (s->buf_end - s->buffer) + (1<<16)){
> >>        while(s->pos < offset && !s->eof_reached)
> >>            fill_buffer(s);
> >>        s->buf_ptr = s->buf_end + offset - s->pos;
> >>
> >>if eof_is_reached then s->pos might be < offset, therefore buf_ptr might
> >>be > buf_end. Next get_buffer will memcpy negative size:
> >>
> >>int get_buffer(ByteIOContext *s, unsigned char *buf, int size)
> >>{
> >>    int len, size1;
> >>
> >>    size1 = size;
> >>    while (size > 0) {
> >>        len = s->buf_end - s->buf_ptr;
> >>        if (len > size)
> >>            len = size;
> >>        if (len == 0) {
> >>	   [...]
> >>	} else {
> >>	    memcpy(buf, s->buf_ptr, len);
> >>            buf += len;
> >>	[...]
> >>
> >>Note that url_fseek clear eof_reached.
> >>
> >>That will only happen when reading a streamed file.
> >>Im submitting the attached patch, but Im not sure what the correct
> >>behaviour should be. Any suggestion welcome.
> > 
> > 
> > i think returning some error for attempts to seek after the end of the
> > file seems appropriate
> > 
> 
> Ok, patch attached.

i think this is buggy, that is if the seek is slightly to before EOF
fill_buffer() could still set EOF as the end of the buffer is further
ahead

[...]
-- 
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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