[linux-dvb] Re: vbv delay/buffer overflows on VBR statmux

[Oliver Endriss <o.endriss@gmx.de>]

Gregor Lawatscheck wrote:
> Some things I wanted to say:
>
> 1) Could it be a problem under certain conditions that the vbv buffer
> size is bigger than the actualy buffer set aside in the firmware? Of
> all the streams I've seen so far the vbv buffer size is 224 kbyte, as
> Ralph says the video memory in the firmware is at 210 k now. I
> suppose if settitng the bitrate alone doesn't save us from ARM
> crashes and if nothing can be done about freeing another 20k (to be
> safe) from the firmware I suppose we could try patching that value
> too. But let's see how far we get.

I do not understand why the firmware has problems with *low-bitrate* 
streams. If buffer space is limited I would rather expect problems with 
high-bitrate streams.

> 3) The remaining two bits of the 10th byte aren't patched yet so on
> certain bitrates higher than 26.2 Mbit it wouldn't actually patch it
> to 15 MBit - but it's fairly unlikely to have such a high bitrate
> even on VBR.

The two bits in byte 10 are the *low* significant bits! If they are set, 
the bitrate would be increased by 1200 bits/s max. These bits are 0 in 
all streams I have seen.

> Great job devising and optimizing these patches Oliver, I don't
> notice much (or any) CPU impact as long as there is no logging. Let's
> just hope setting the bitrate avoids lockups and ARM crashes over
> here. I'll report once I have some more data.

If this patch will ever find its way into CVS, I'll add a module 
parameter to disable it completely.

Oliver


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