[FFmpeg-devel] [RFC] using ByteIOContext with buffer without reading function
Baptiste Coudurier
baptiste.coudurier
Sun Apr 12 00:52:44 CEST 2009
Hi Michael,
On Fri, Mar 20, 2009 at 04:36:04AM +0100, Michael Niedermayer wrote:
> On Sun, Mar 15, 2009 at 03:53:07PM -0700, Baptiste Coudurier wrote:
> > Hi,
> >
> > I notice something strange when using ByteIOContext with a supplied
> > buffer without read function, reading only.
> >
> > aviobuf.c
> > init:
> > if(!read_packet && !write_flag){
> > s->pos = buffer_size;
> > s->buf_end = s->buffer + buffer_size;
> > }
> >
> > seek:
> > if (!s->must_flush &&
> > offset1 >= 0 && offset1 < (s->buf_end - s->buffer)) {
> > /* can do the seek inside the buffer */
> > s->buf_ptr = s->buffer + offset1;
> >
> > mov.c:
> > if(init_put_byte(&ctx, moov_data, moov_len, 0, NULL, NULL, NULL,
> > NULL) != 0)
> > goto free_and_return;
> >
> > Problem is:
> > when you use url_fskip on the ByteIOContext, for example to skip
> > everything not read (size is 51, url_fskip(51)), you will end up seeking
> > at s->buf_end.
> >
> > However the condition in "seek" won't allow this since offset1 ==
> > s->buf_end - s->buffer.
> >
> > Would it be better to change init to set buf_end to s->buffer +
> > buffer_size + 1 or check for <= in seek ?
>
> i would guess to <= in seek but this should be carefully tested, iam
> not sure if this might have some unexpeted sideeffects
>
Any confidence in the <= case ?
I've checked the buf_end tests in aviobuf.c and they seem ok.
It would be nice to move on on the multiple stsd feature. This should be a
good step in exporting the struct to decoders needing it.
--
Baptiste COUDURIER GnuPG Key Id: 0x5C1ABAAA
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