Comment 45 for bug 602934

(In reply to comment #32)
> (In reply to comment #31)
> >> I think you will be able to repro it on Windows (and I assume on FFmpeg 0.6.1
> >> too, but I have not tried with 0.6.1 yet). What happens on Mac?
> >
> > Same sort of thing. If I create a mono M4A file using 0.6.1 and then try to
> > import it using a v0.5 library, it will always import as stereo.
> So if you import the 0.6.1-created mono file on Mac using 0.6.1, it's mono? A
> mono M4A created by Audacity on Ubuntu using 0.6.1 still imports as stereo into
> Audacity on Windows using FFmpeg 0.6.1 (as supplied in your installer).
>

Now that I have the v0.6.1 build working on the Mac, I'll try some more things.
 I thought it might be a difference between our older 0.5.x version and 0.6.1,
, but I've proven to myself that's not the case. I've also proven to myself
that it's not a case where a file is exported using the native encoder and
imported with faad or vice versa.

Using a v0.6.1 + faac/faad and the native aac disabled, I exported a 30 second
chirp and then imported it. It went out as a mono file and came back in as
stereo. This was with no library changes between...just out and in.

> > The only time I got the 3 - 4 times slower exports was after I'd imported an
> > OGG file.
> I never use OGG files so it's not an explanation for me. Also speed of WMA and
> AC3 exports are comparable to other formats for me.
>
> So for you (from a generated tone), how much slower are M4A exports using "M4A
> Files" and FFmpeg-with-native-AAC encoder, compared to other formats?

I used a 10 minute, mone tone for the following. (This is on the Mac)

ffmpeg 0.6.1 + faac/faad:
11 seconds to WMA
11 seconds to AC3
28 seconds to M4A (imported as stereo using faad, imported as mono using
native)

ffmpeg 0.6.1 + native:
11 seconds to WMA
11 seconds to AC3
16 seconds to M4A (imported as stereo using faad, imported as mono using
native)

I used the "faad" command line tool to read in both native and faac exported
files and both of them are reported by faad as 2 channels:

/Users/yam/10n.m4a file info:

LC AAC 599.418 secs, 2 ch, 44100 Hz

tool: Lavf52.64.2

/Users/yam/10f.m4a file info:

LC AAC 599.348 secs, 2 ch, 44100 Hz

tool: Lavf52.64.2

I also used the "faac" command line too to create the m4a directly and it also
imported as stereo using faad and mono using native aac.

So, to summarize:

1) No extreme time differences between m4a and other ffmpeg formats.
2) The native exporter is faster than faac
3) Faac exported files sound better
4) Any file imported with faad gets imported as stereo

This was all done on the Mac...

Leland