[FFmpeg-devel] [PATCH] movtextdec: MPEG4 Part 17 Timed Text Decoder.

Yusuke Nakamura muken.the.vfrmaniac at gmail.com
Thu Jul 5 17:06:54 CEST 2012

> > > + * 3GPP TS 26.245/MPEG4 Part 17 Timed Text decoder
> >
> > All that naming looks quite inconsistent: you use "mov
> > text" (sometimes "MPEG4 Timed Text"), but the specs are the MPEG-4
> > ones, and are talking about "3GPP Timed Text" (and sometimes called
> > "tx3g" right?) so wouldn't it make sense to actually call that
> > decoder tx3gdec.c?
> >
> > AFAICT all of this is the same thing. Eventually you could add a @file
> > doxy to briefly give the good references, but I don't want to block
> > this patch.
> Yeah, the thing is that its the same thing with a lot of different
> names. I only use mov_text because the codec id already exists in the
> codebase - I wouldn't have called it that if I had a choice.
> * 3GPP TS 26.245 defines the stream content
> * MPEG4 Part 17 defines how it gets muxed into mp4 containers
> * TX3G is the FOURCC but doesn't reflect any official naming
> I obviously can't use all those names in every spot, so I ended up
> using MPEG4 Part 17 as the "short" form, just because this hasn't
> been tested in any other context - so I don't want to claim it will
> work for any other container.
I don't recommend you use MPEG4 Part17 as the "short" form.
MPEG-4 Part17 defines structure of __streaming__ timed text format.
MPEG-4 Part17 refers to 3GPP TS 26.245 as one example to fragment timed
text sample into TTUs.
(Streaming timed text access unit consists of concatenation of TTUs, not
simple text string + text modifiers.)
Therefore, if you use MPEG-4 Part17, the decoder should extract text sample
(text string + text modifiers) and sample description from TTUs and decode
them, or just extract them.
As long as this decoder decodes only 3GPP or QuickTime form timed text
stream, it is not an MPEG-4 Part17 decoder.

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