MODULE FOR I, P FRAME

[Rhodri James]

On Tue, 23 Feb 2010 10:39:21 -0000, DANNY <danijel.gvero at gmail.com> wrote:

> @James I am thinkinhg about effect of errors that are within the
> sequence of P frames. Where the P frames have only the information
> about the changes in previous frames, so that errors are present until
> the next I frame. So I would like to see how is this seen in different
> GoP sized clips.

Ah, I see.  What I'd suggest you do is to encode your video clip at  
various GOP sizes (you'll want some quite extreme ones for comparison),  
then write a little program that reads in the file byte by byte and  
randomly corrupts the data as it goes through.  "tsplay" from the tstools  
suite that I mentioned earlier will do that for you (because it was very  
handy for testing the robustness of our decoders).  Then watch the results  
using VLC or similar.

My recollection is that when the image isn't static, P frames tend to have  
enough intra-coded blocks that corrupted video data doesn't have as much  
effect as you might think.  I've dealt with streams that had ten seconds  
or more between I frames, and starting at a random spot (simulating  
changing channel on your digital TV) builds up an intelligible (if  
obviously wrong) image surprisingly quickly.

PS: my first name is Rhodri, not James.  Don't worry, it catches a lot of  
people out.

-- 
Rhodri James *-* Wildebeeste Herder to the Masses