[linux-dvb] Re: video pts differences on dvb-t in the uk

[Måns Rullgård <mru@mru.ath.cx>]

Ragnar Sundblad <ragge@nada.kth.se> writes:

> --On den 10 oktober 2004 23:43 +0200 Måns Rullgård <mru@mru.ath.cx> wrote:
>
>>>> But surely the difference should be detectable in some way?
>>>
>>> Sure, just compare the PTS fields? I probably don't
>>> understand your question.
>>
>> There is no requirement for the PTS values in different streams to
>> ever be equal.  The only requirement is that a PTS is present in all
>> streams at least once every 0.7 seconds.
>
> But there should be specified somewhere how much they may
> differ, which equals to how much buffer a decoder must have.
> I even suspect that his lagging audio thing may even be
> according to some spec, since most DVB streams seems to
> have it.
>
> Do you happen to know if there is any document that says
> anything about this?

For MPEG1 audio, the buffer size in the TS STD as defined in ISO
13818-1 is 3584 bytes.  For video, the buffer size is given by the
vbv_buffer_size field in the sequence header.  For MP@ML this is
limited to 1835008 bits.  At typical DVB bitrates, this is roughly 300
ms.

These values are specified by ISO 13818-1 and -2.  ETSI TR 101 154
states that any DVB receiver must be capable of decoding anything
within the ISO specs.

-- 
Måns Rullgård
mru@mru.ath.cx