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

Christophe Massiot massiot at via.ecp.fr
Mon Mar 20 12:22:03 CET 2006

On Sat, Mar 18, 2006, Robert Scheffler wrote:

> The requirement is that every access unit in the video elementary stream
> should be aligned to a PES header. That is the first byte of each PES packet
> payload is the first byte of an access unit. The data_alignment_indicator
> bit should also be set in the PES header. This type of alignment corresponds
> to an alignment_type of two in the data_stream_alignment_descriptor. This
> alignment requirement is dictated in the USA CableLabs VOD Content Encoding
> Profiles, and is used in all US Cable System VOD deployment. So it isn’t
> just my weird situation. I would think this should be useful to others as
> well.
> The error I am having means that the ingest analyzer on the server receiving
> device has not detected a picture header within two transport packets of
> PUSI being set for the video PID (counting only video PID packets). There
> are circumstances when the streaming chip needs to alter the picture header
> and extension and its offsets are limited to two packets.
> Måns commented:
> OK, I think I understand the problem.  IIRC the VLC muxer uses a more
> typical approach of ~2k size PES packets with no specific alignment
> constraints. Modifying it to produce the type of stream you want shouldn't
> be difficult, though.
> The question is can anyone modify the VLC muxer to allow this alignment
> option?
> I would be greatly appreciative of any effort to help me with this
> non-standard alignment.

I have just added a --sout-ts-alignment option which you should set to
1. However, I have re-implemented the old behaviour, meaning that access
units are always aligned, but the data_alignment flag in the PES header
has never been set. Tell me if it is a problem.

Christophe Massiot.

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