[MPlayer-users] misdetected wav with default demuxer

[Andy Furniss]

Carl Eugen Hoyos wrote:
> Andy Furniss <adf.lists <at> gmail.com> writes:
>
>> http://www.datafilehost.com/d/2b546e2d
>
> Which sample is this?
> (Which file on http://www.ambisonia.com assuming that is
> where it comes from.)
> The reason I ask is that the file is not supposed to play
> at all (it contains four channels with content != center
> or left or right) but it plays fine here with old FFmpeg
> which makes me wonder if this really is an ambisonic file
> (or if I misunderstand the definition).

The file is part of the TetraMic Sample from -

http://ambisonic.info/audio/paulhodges/others.html

I just tried some more from there and the first one on that page 
(Hildegard & Wilbye) also fails, but the second and third don't and 
neither do some of the other pwh* I have from ambisonia - seems a bit 
hit and miss.

As for the channels I don't know what you mean (or how to look for that 
info to see if it's relevant to this issue).

 From what .amb files I have I do see that some are just normal wavs and 
some (like these) do at least have the GUID set - which causes current 
ffmpeg to comment -

[NULL @ 0x17d9be0] unknown subformat:010000002107d3118644c8c1ca000000
[wav @ 0x17d9140] Stream #0: not enough frames to estimate rate; 
consider increasing probesize
[wav @ 0x17d9140] Estimating duration from bitrate, this may be inaccurate
[wav @ 0x17d9140] Could not find codec parameters for stream 0 (Audio: 
none, 44100 Hz, 4 channels, 2822 kb/s): unknown codec
Consider increasing the value for the 'analyzeduration' and 'probesize' 
options
pwh-GeorgianFolksongs.amb: could not find codec parameters

but happily mplayer still plays them, though as I said -demuxer lavf is 
suboptimal WRT seeking and -demuxer audio is OK and doesn't fail.

Of course ambisonic files are just audio and do (in a way) "play fine" 
until you compare the mix with a properly decoded version (even if you 
don't have enough speakers for real surround ambdec can make a stereo 
mix and with supercollider + ambisonic tool kit you can make hrtf 
binaural from them - so I do think they are valid if not to the letter 
of the spec, which says that "WAVE_EX dwChannelMask field should be set 
to zero".

I don't know if that's what you are referring to but as long as mplayer 
just plays it as a wav with the channel order "as is" I think that's 
fine (assuming mplayer doesn't usually reorder wav channels  - my 
understanding is low here).

If somebody plays a .amb or a plain wav with wxyz in the name I don't 
think mplayer should care - IMHO it's up to the user to set things up 
for proper playback.