Re: [VCDImager Bugs/Devel] problems with vcdimager 0.7.x

[Herbert Valerio Riedel]

On Thu, 16 Aug 2001, Arnd Bergmann wrote:

> On Wed, 15 Aug 2001 address@hidden wrote:
> I am pretty sure this is a bug. The parse_user_data function
> does not seem to consider the fact that user_data() in the MPEG
> standard can contain any data and not just what may be in
> allowed for VCD. My guess is that either tmpeg inserts some
> user data of its own (e.g. 'encoded with tmpeg1.2a at ...') or
> bbmpeg inserts invalid scan information.

well, for (S)VCDs the concerned user data id has a fixed syntax...

bbmpeg is known to insert correct scan information... I would trust bbmpeg
more (even if its source code looks quite bad) than tmpgenc (of which
the source code is hidden from mankind)...

> The patch below is a quick fix for the problem, but I don't
> have the (S)VCD standard, so I can't tell if it might miss
> scan data now.

for user data with the scan data id,  the length is fixed to 14, it's the
same for VCD2.0 as well btw, any other length may confuse firmwares...

> Hvr probably wants the beginning of the MPEG file to
> give a more complete analysis, the interesting part is
> whatever follows '000001b2'.

that would surely help... :-)

> Arnd <><
>
> --- libvcd/vcd_mpeg.c   2001/08/15 08:18:16     1.1.1.3
> +++ libvcd/vcd_mpeg.c   2001/08/15 22:06:00
> @@ -326,7 +326,11 @@
>            {
>              struct vcd_mpeg_scan_data_t *usdi = (void *) udg;
>              vcd_assert (sizeof (struct vcd_mpeg_scan_data_t) == 14);
> -            vcd_assert (usdi->len == 14);
> +            if (usdi->len != 14)
> +              {
> +                vcd_debug ("invalid scan information (len=%d) found", 
> usdi->len);
> +                return;
> +              }
>              _check_scan_data ("previous_I_offset", &usdi->prev_ofs, state);
>              _check_scan_data ("next_I_offset    ", &usdi->next_ofs, state);
>              _check_scan_data ("backward_I_offset", &usdi->back_ofs, state);
> @@ -342,7 +345,7 @@
>            break;
>
> -        default:
> -          break;
> +        default: /* any unknown user data */
> +          return;
>          }
>
>        pos += udg->len;
>
>
>
>
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Herbert Valerio Riedel       /    Phone: (EUROPE) +43-1-58801-18840
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