midi to ogg - pipeline distortion - audio

Question

I am trying to convert midi files to ogg or mp3. Eventually this will happen on a linux webserver but currently I am using a Windows 7 machine. I am using timidity to convert the midi to wav and then either sox or ffmpeg to convert the wav to ogg/mp3.
When I use an intermediate file the process works fine (in the first line below timidity creates file.wav)
timidity.exe file.mid -Ow
sox.exe file.wav file.ogg
However, when I try to pipe the timidity output into sox (as below), the resulting file ogg is horribly distorted
timidity.exe file.mid -Ow -o - | sox.exe -t wav - file.ogg
and I get a warning
sox.exe WARN wav: Premature EOF on .wav input file
I also get the same distortion problem when I replace sox with ffmpeg (and the appropriate command line options), or when I replace ogg with mp3 as the output format.
So what am I doing wrong?
Thanks,
Chris

Answer 1

Regarding the warning itself, you're doing nothing wrong. You may also see a warning from timidity that reads something like
Warning: -: Illegal seek: Can't make valid header
What's happening there is explained in the timidity manual page:
If output is directed to a non-seekable file, or if TiMidity++ is interrupted before closing the file, the file header will contain 0xffffffff in the RIFF and data block length fields.
Note that RIFF is the encoding format commonly called by its file extension, .wav. When timidity writes a RIFF file, it doesn't know how long the file will be, so it writes some placeholder junk in the header and moves on to writing the data. When it finishes with the data, it knows how long the file is, so it goes back to the beginning of the file and writes over that junk in the header. When you write to a pipe, it has no way to go back and rewrite anything: the downstream program has to handle the placeholder junk. Also from the timidity manual page:
The popular sound conversion utility sox is able to read such malformed files, so you can pipe data directly to sox for on-the-fly conversion to other formats.
Thus, the message you mentioned. Sox is informing you that the chef prepared the file wrong BUT SOX IS HAPPY TO EAT IT ANYWAY BECAUSE SOX IS NOT PICKY. Sox is apparently passive-aggressive. Who knew?
You can ignore those warning messages, because now they are telling you something you already know. Or, you can use a raw format and explicitly tell timidity and sox how to play well with one another:
timidity file.midi -Or1Ssl -s44.1 -o- | sox -t raw -b 16 -e signed -r 44.1k -c 2 - file.ogg
As for the distortion, that may be caused in part by quirks in the audio libraries on the Windows system. I note that the pipeline in the question, sans .exe extensions, produces output with no notable distortion on a linux system. Using a well-defined raw format in the pipeline may also help with that issue.
Note that for Ogg output, you can now get that directly from timidity:
timidity file.midi -o file.ogg -Ov