[vdr] Re: Nasty bug in StillPicture()

[Klaus Schmidinger <Klaus.Schmidinger@cadsoft.de>]

Oliver Endriss wrote:
> 
> On Wednesday 15 October 2003 18:47, Stefan Huelswitt wrote:
> > But, in the meantime I found out that this particular bug is a
> > side effect of the AC3overDVB patch and doesn't happens with
> > plain VDR.
> >
> > With plain VDR all non-video packets are stripped from the data
> > buffer before passing it to StillPicture().

Maybe it's not a bad idea to strip these here, anyway, while we're
already scanning the data. This could later even lead to defining
cDevice::StillPicture() as "audio safe".

> Anyway, the range check should be added to the next vdr release.

I have also received a patch from Thomas Heiligenmann which adds
handling of MPEG1 frames.

Here's the complete cDvbDevice::StillPicture(). Please take a look
at it and let me know if this is ok (especially the part marked
"MPEG-1 PES header", since I haven't tested that myself):

void cDvbDevice::StillPicture(const uchar *Data, int Length)
{
#define VIDEO_STILLPICTURE_WORKS_WITH_VDR_FRAMES
#ifdef VIDEO_STILLPICTURE_WORKS_WITH_VDR_FRAMES
  if (Data[0] == 0x00 && Data[1] == 0x00 && Data[2] == 0x01 && (Data[3] & 0xF0) == 0xE0) {
     // PES data
     char *buf = MALLOC(char, Length);
     if (!buf)
        return;
     int i = 0;
     int blen = 0;
     while (i < Length - 6) {
           if (Data[i] == 0x00 && Data[i + 1] == 0x00 && Data[i + 2] == 0x01) {
              int len = Data[i + 4] * 256 + Data[i + 5];
              if ((Data[i + 3] & 0xF0) == 0xE0) { // video packet
                 // skip PES header
                 int offs = i + 6;
                 // skip header extension
                 if ((Data[i + 6] & 0xC0) == 0x80) {
                    // MPEG-2 PES header
                    offs += 3;
                    offs += Data[i + 8];
                    len -= 3;
                    len -= Data[i + 8];
                    }
                 else {
                    // MPEG-1 PES header
                    while (offs < Length && len > 0 && Data[offs] == 0xFF) {
                          offs++;
                          len--;
                          }
                    if ((Data[offs] & 0xC0) == 0x40) {
                       offs += 2;
                       len -= 2;
                       }
                    if ((Data[offs] & 0xF0) == 0x20) {
                       offs += 5;
                       len -= 5;
                       }
                    else if ((Data[offs] & 0xF0) == 0x30) {
                       offs += 10;
                       len -= 10;
                       }
                    else if (Data[offs] == 0x0F) {
                       offs++;
                       len--;
                       }
                    }
                 if (blen + len > Length) // invalid PES length field
                    break;
                 memcpy(&buf[blen], &Data[offs], len);
                 i = offs + len;
                 blen += len;
                 }
              else if (Data[i + 3] >= 0xBD && Data[i + 3] <= 0xDF) // other PES packets
                 i += len + 6;
              else
                 i++;
              }
           else
              i++;
           }
     video_still_picture sp = { buf, blen };
     CHECK(ioctl(fd_video, VIDEO_STILLPICTURE, &sp));
     free(buf);
     }
  else {
     // non-PES data
     video_still_picture sp = { (char *)Data, Length };
     CHECK(ioctl(fd_video, VIDEO_STILLPICTURE, &sp));
     }
#else
#define MIN_IFRAME 400000
  for (int i = MIN_IFRAME / Length + 1; i > 0; i--) {
      safe_write(fd_video, Data, Length);
      usleep(1); // allows the buffer to be displayed in case the progress display is active
      }
#endif
}


Klaus


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