A quick hack to prevent segfault. However this should not be incorrect i...

...n the first place.

The segfault occurs in vp8_parser.c line 30:

```c
s->pict_type= (buf[0]&0x01) ? AV_PICTURE_TYPE_P : AV_PICTURE_TYPE_I;
```

buf is NULL. It appears that the AVPacket object has been corrupted at some earlier point. See my quickhack branch for a test that might be useful in tracking this to its source.