Option "bitrate=32k" fails silently when exporting to ogg.

[BreadMaker]

I have this script that I use to maintain a music database. So far I have no problems, the files are exported to ogg format and stored in the database, but I've noticed that the quality options (intended to reduce the final size of the DB) are ignored completely. I tried both the bitrate and the parameters options.

preview.export("tmp.ogg", "ogg", codec="libvorbis", parameters=["-aq", "1", "-ab", "32k"])

preview.export("tmp.ogg", "ogg", codec="libvorbis", bitrate="64k")

I've done some tests in mp3, and the quality options work as they should. My question is: Do I need some library (libav seems to be installed), or I found a bug?

In case you were wondering, I prefer to use ogg for its best quality/size ratio compared to mp3.

I'm using python 2.7.6 and pydub 0.9.5. Don't know if relevant, but I'm using a 64-bit GNU/Linux system.

[BreadMaker]

After reading through a lot of different documentations, I have found the correct parameters for avconv, adding -ab (non-existent) made the important parameter -aq be ignored. bitrate keeps ignored. This info should be documented.

BTW, the corrected (and working as expected) line is:

preview.export("tmp.ogg", "ogg", codec="libvorbis", parameters=["-aq", "0", "-ar", "32000"])

[BreadMaker]

I've been trying different settings and I've noticed something, the bitrate parameter has always worked, but not the way I expected.

Now the following happens: bitrate="64k" works but bitrate="32k" fails silently. The lowest option that works for me is bitrate="48k" that generates a much smaller file (just what I need)

preview.export("tmp.ogg", "ogg", codec="libvorbis", bitrate="48k")

After this odyssey, I conclude that pydub is a great project, but unfortunately requires more documentation.

[jiaaro]

@BreadMaker thanks for the bug report! I've been working on docs (even wrote some today!) but there's a lot to cover, especially for the export method, since it covers much of the functionality of ffmpeg.

I will update the docs with your notes when I'm back at my computer :)

Thanks again!

[jiaaro]

@BreadMaker After further research, each codec has it's own rules about acceptable bitrates. The ffmpeg documentation is pretty light on details but does have some info on bitrate arguments.

[BreadMaker]

Cool, if you add an statement about that in the export docstring, I think we can close this issue.