Re: [ecasound] Wanted: examples of using the file update/readwrite mode

On Sun, 19 Sep 2010, Joel Roth wrote:

> I see that the -X flag sets this mode, but how does it work
> in practice?

Adding to the replies you already got: -X (which is the default), all
outputs are opened in update mode. This allows to extend an existing file
with new content, or replace portion/segments its contents.

The overwrite/truncate mode (-x, not the defaults), the output file is
truncated to zero length before processing is started. This happens when
the chainsetup is connected. The semantics match the O_TRUNC flag for
open system call.

So by default ecasound works in update mode. This basicly matches how old
tape recorders work. You can replace portions of the recording by seeking
to the wanted location and pressing 'rec', and stopping before replacing
anything you want to keep. By forwarding to the end of current recording,
one can record new stuff at the end. Of course in digital domain, both
number of tracks, and their length are in effect unlimited.

The truncate mode, OTOH, is same as erase the whole tape the minute you
press 'rec' (despite the current location).

Some gotchas:
  - Audio object types have limitations and not all support output mode.
    E.g. one cannot update mp3 and ogg outputs even if you specify -X.
    This applies generally to all encoded formats, as well to formats
    that do not support seeking. One exception is flac when using
    libsndfile.

> I'm contemplating a punch-in/punch-out function.
> Perhaps this mode will help me...

For punch-in/out, probably a better alternatige (than updating existing
takes), is to record a new track that only has audio for the punch-in part
(seek to punch-in location and start recording).

Then when mixing down, mix the original take out during the punch-in
section and mix the punched in track up. This allows for more freedom to
select the punch-in location (e.g. when you start recording the punch-in
track, and which parts of the punched-in new recording you really want to
use in final mix). By replacing the actual original take, you get many of
the downsides of traditional tape machines (which can be easily avoided in
digital domain).

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Received on Sat Sep 25 16:15:01 2010