[FFmpeg-devel] [PATCH] Demuxer for Leitch/Harris' VR native stream format (LXF)

[Michael Niedermayer]

On Mon, Sep 13, 2010 at 08:44:00PM +0100, M?ns Rullg?rd wrote:
> Michael Niedermayer <michaelni at gmx.at> writes:
> 
> > On Mon, Sep 13, 2010 at 10:56:43AM +0100, M?ns Rullg?rd wrote:
> >> Tomas H?rdin <tomas.hardin at codemill.se> writes:
> > [...]
> >> >> > +//reads and checksums packet header. returns format and size of payload
> >> >> > +static int get_packet_header(AVFormatContext *s, unsigned char *header,
> >> >> > +                             uint32_t *format)
> >> >> > +{
> >> >> > +    LXFDemuxContext *lxf = s->priv_data;
> >> >> > +    ByteIOContext   *pb  = s->pb;
> >> >> > +    int size, track_size, samples;
> >> >> > +    AVStream *st;
> >> >> > +
> >> >> > +    if (get_buffer(pb, header, LXF_PACKET_HEADER_SIZE) != LXF_PACKET_HEADER_SIZE)
> >> >> > +        return AVERROR(EIO);
> >> >> > +
> >> >> > +    if (memcmp(header, LXF_IDENT, LXF_IDENT_LENGTH)) {
> >> >> > +        av_log(s, AV_LOG_ERROR, "packet ident mismatch - out of sync?\n");
> >> >> > +        return -1;
> >> >> > +    }
> >> >> > +
> >> >> > +    if (check_checksum(header))
> >> >> > +        av_log(s, AV_LOG_ERROR, "checksum error\n");
> >> >> > +
> >> >> > +    *format = AV_RL32(&header[32]);
> >> >> > +    size    = AV_RL32(&header[36]);
> >> >> > +
> >> >> > +    //type
> >> >> > +    switch (AV_RL32(&header[16])) {
> >> >> > +    case 0:
> >> >> > +        //video
> >> >> > +        //skip VBI data and metadata
> >> >> > +        url_fskip(pb, AV_RL32(&header[44]) + AV_RL32(&header[52]));
> >> >> 
> >> >> cant this lead to a backward seek and thus infinite loop ?
> >> >
> >> > Yes, assuming AV_RL32() returns signed. Fixed by casting to uint32_t and
> >> > splitting up into two skips.
> >
> > split is ugly
> >
> >> 
> >> AV_RL32() returns an unsigned value.
> >
> > maybe it should but i dont think it does
> >
> > #   define AV_RL32(x)                           \
> >     ((((const uint8_t*)(x))[3] << 24) |         \
> >      (((const uint8_t*)(x))[2] << 16) |         \
> >      (((const uint8_t*)(x))[1] <<  8) |         \
> >       ((const uint8_t*)(x))[0])
> 
> You are right.  Should we change it?

i do not know, but at least we should make sure all implementations of AV_R*
are consistent in terms of signedness

--
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

No human being will ever know the Truth, for even if they happen to say it
by chance, they would not even known they had done so. -- Xenophanes
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