[theora] Add an intro to a theora file without re-encoding?

[Michael Opdenacker]

On 07/17/2009 06:55 AM, yorn at gmx.net wrote:
> Hey Michael,
> How do you produce the "silence"? Sounds as if it was not a vorbis stream!?
>
> The message "We got a real problem ... " is a bit missleading ;-). This usually means the stream ends invalid (e.g. there is no End-Of-File indicator or a packet is corrupt because it is read from a livestream etc). oggCat tries (mostly successfully) to create a valid stream also in such situations.
>   
Here's how I produce this file now. I found a silence file on the
Internet (http://free-electrons.com/issues/oggcat-jul17-2009/silence.wav
about 1 minute long), and I convert it to vorbis with the same bitrate
and sample rate as my main video:

oggenc --managed --bitrate=112 --resample 48000 silence.wav

Here's the result:
http://free-electrons.com/issues/oggcat-jul17-2009/silence.ogg

Now, I want to cut it to 6 seconds (that's the duration of my video intro):
oggCut -i silence.ogg -o silence6s.ogg -e 6000

However, the new file is shorter than 6s! (see
http://free-electrons.com/issues/oggcat-jul17-2009/silence6s.ogg)

> ogginfo silence6s.ogg
Processing file "silence6s.ogg"...

New logical stream (#1, serial: 476dbad9): type vorbis
Vorbis headers parsed for stream 1, information follows...
Version: 0
Vendor: Xiph.Org libVorbis I 20070622 (1.2.0)
Channels: 2
Rate: 48000

Nominal bitrate: 112.000000 kb/s
Upper bitrate not set
Lower bitrate not set
Vorbis stream 1:
    Total data length: 537 bytes
    Playback length: 0m:05.387s
    Average bitrate: 0.797327 kb/s
Logical stream 1 ended

That's weird: even if I use "-s 10000", I still get this 5.387s lenght.
The input silence.ogg file looked good though:

> ogginfo silence.ogg
Processing file "silence.ogg"...

New logical stream (#1, serial: 628dbaa3): type vorbis
Vorbis headers parsed for stream 1, information follows...
Version: 0
Vendor: Xiph.Org libVorbis I 20070622 (1.2.0)
Channels: 2
Rate: 48000

Nominal bitrate: 112.000000 kb/s
Upper bitrate not set
Lower bitrate not set
Vorbis stream 1:
    Total data length: 5952 bytes
    Playback length: 0m:59.999s
    Average bitrate: 0.793600 kb/s
Logical stream 1 ended

Any idea why?
> I have a small program to create silence (in wave). I then use oggenc with the same parameters as from the subsequent audio stream and I have had no problems. I've used that method for my video tutorial. 
>   
Is this program available somewhere? I'd love to try it too.

Many thanks for your help.

Cheers,

Michael.

-- 
Michael Opdenacker, Free Electrons
Kernel, drivers and embedded Linux development,
consulting, training and support.
http://free-electrons.com
+ 33 621 604 642