[FFmpeg-devel] [PATCH] movtextdec: MPEG4 Part 17 Timed Text Decoder.
muken.the.vfrmaniac at gmail.com
Fri Jul 6 10:11:07 CEST 2012
2012/7/6 Philip Langdale <philipl at overt.org>
> On 05.07.2012 08:06, Yusuke Nakamura wrote:
>> 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
>> (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.
> Yes, you make a very valid point. Man, this stuff makes my head hurt. I
> stick to "3GPP Timed Text" as the description. Do you have access to
> that actually use TTUs? I've never seen one or tools that will write them
> an mp4 container.
I've also never seen even in reference softwares and conformance testing
files though streaming timed text can be stored into MP4 container and
MPEG-2 TS/PS (13818-1:2007 Amd1).
Probably, samples that use TTUs are in MPEG working files but I don't have
access to them.
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