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Subject: Re: [PATCH] mp2 filenames
From: Dave Chapman (dave_at_dchapman.com)
Date: 2002-08-28


On Wednesday 28 August 2002 12:48, Björn Stenberg wrote:
> Dave Chapman wrote:
> > I finally bought an Archos JBR20 and my first patch is to allow me to
call
> > my Layer 2 files ".mp2".
> >
> > In fact, the included patch allows all filenames ending with ".mp?". If
the
> > maintainers don't like that, then I would suggest that ".mp3", ".mp2" and
> > ".mpa" all be recognised as legal MPEG audio files.
>
> What is ".mpa"? I've never seen anyone use that.

You're going to regret asking that :-)

It's commonly used in the MPEG video world - if you "demultiplex" an MPEG
video file into the audio and video "elementary streams" then you would
commonly call the two resulting files "file.mpv" and "file.mpa".

There are many different types of "MPEG file". It may help if I briefly
describe the various MPEG file formats:

1) Elementary streams (ES) - the raw data. Files known as "mp3" are "mpeg
audio" elementary streams. You can also have "mpeg video" elementary streams
as well as data streams.

2) Packetised elementary streams (PES) - generated by splitting your ES into
packets (e.g. 4096 bytes for audio streams), and putting a "PES header" at
the start of each packet containing meta-data about the stream - e.g. a
timestamp for synchronising decoding of multiple streams.

3) Program Streams (PS) - these consist of a set of related PES streams (e.g.
video and audio) "multiplexed" together. "VOB" files on DVDs are PS files
(but with some extra "system" packets inserted for navigation etc).

4) Transport Streams (TS) - these consist of PES streams split into tiny 188
byte packets (including the TS header). DVB (the standard for European
digital satellite TV and radio) broadcasts using Transport Streams (with on
average 6 TV channels in a single TS).

The transformation to PES streams from either a PS/VOB or TS is trivial. So
is the removal of the PES headers to generate an elementary stream.

Is there any interest in this functionality (i.e. playing the audio parts of
video files containing MPEG audio) in Rockbox?

> A problem is that windows types tend to name their MPEG movies ".mpg".

Agreed. So should I commit a patch that only allows "mp3", "mp2" and "mpa" ?

Dave.



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