Implementation of PET (continued)
In the following two demonstration MPEG streams, encoded packets were
randomly thrown away in order to simulate a lossy medium. The
following viewgraph shows the number of packets sent (red steps) and
received (green steps) per message. The MPEG sequence "Red's Nightmare"
was encoded into 41 messages, encoding one whole GOP at a time. A GOP
consists of 1 I frame, 2 P frames and 27 B frames. The whole sequence
encompasses 1210 frames and the packet size was set to 2000 bytes.
![[Packet Loss Statistics]](GIFS/MPEG_packet_loss_stats_small.gif)
The following viewgraph shows the absolute number of packets lost per
message/GOP:
![[Absolute Packets Lost]](GIFS/MPEG_packet_loss.gif)
On the destination side the received packets were decoded and missing
frames were substituted by "dummy" B frames which repeat the last
correctly decoded frame.
Demos
To see the demonstration of how PET protects the MPEG stream,
choose one of the following:
- The following is the stream that was discussed earlier:
![[Red's Nightmare]](GIFS/MPEG_red_small.gif)
- This is another demo, a hockey MPEG sequence with a GOP pattern of
IBBPBBPBBPBBPBB:
![[Hockey Sequence]](GIFS/MPEG_hockey_small.gif)
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![[Packet Loss Statistics]](GIFS/MPEG_packet_loss_stats.gif)