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

Måns Rullgård mru at inprovide.com
Fri Mar 17 00:24:59 CET 2006

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

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