[vlc-devel] Re: Is there a way to force PES alignment to a TS boundary when Streaming UDP?

[Måns Rullgård]

Christophe Massiot <massiot at via.ecp.fr> writes:

> On Wed, Mar 15, 2006, Robert Scheffler wrote:
>
>> Let's just say there are many good reasons that makes it in my best
>> interest to stream to this device. It may be abnormal and strange,
>> but I really can not change that. If this can be adjusted inside
>> VLC, then it is a possible connection. If it can not be done in
>> VLC, then I am stuck and will have to try going a different
>> way. Most professional hardware MPEG-2 encoders (Harmonic, GI/Mot,
>> Optibase, and Ligos) can be set to send "aligned", and can feed
>> this device fine. But all of my consumer capture cards and VLC will
>> not send the format that this server likes.
>
> As Måns said, MPEG specifies that a device should be able to cope with
> access units which don't start with at a PES boundary. Sometime between
> 0.8.1 and 0.8.4, I changed the behaviour of the TS mux to build one PES
> per TS for audio streams.
>
> The reason is that MPEG audio streams at low bitrates (64 kbi/s) have a
> frame size of approximately 200 bytes. If we "align" the PES, as you
> say, a frame takes up 2 TS packets, wasting more than 150 bytes per
> frame. I have streams here with 20 audio PIDs at 64 kbi/s, and I can
> tell you that it doubles the bandwidth needed by the audio ESes.

My understanding of the MPEG standard is that the data_alignment_indicator
bit only means that the start of the PES packet is also the start of
an access unit.  It still allows multiple access units per PES packet.

-- 
Måns Rullgård
mru at inprovide.com

-- 
This is the vlc-devel mailing-list, see http://www.videolan.org/vlc/
To unsubscribe, please read http://developers.videolan.org/lists.html