Friday, July 16, 2010

Increasing podcast tempo (playback speed) with Mplayer and Lame

The following commands will re-encode an mp3 file at a faster speed without increasing the pitch and making it sound like a chipmunk. How this actually works is pretty neat.

mplayer -vo null -vc null \
        -speed 1.33 \
        -af scaletempo,volume=0,resample=44100:0:1 \
        -ao pcm:fast:waveheader:file=temp.wav \
lame -b 64 --resample 22.05 temp.wav faster.mp3

It will also set the bitrate to 64kbit which was for compatibility with my old player and to reduce the filesize for some podcasts which are unnecessarily big.

There should be a way to use mkfifo instead of temp.wav, and run the mplayer process and lame at the same time, I'll update this when I figure it out.

Update: The above method broke after upgrading to Ubuntu 11.10 (one or both of mplayer or lame changed something I suspect...), so I swapped it out for the simpler and better SoX:

sox --show-progress --norm source.mp3 dest.mp3 \
    tempo -s 1.33 channels 1 rate 22050

This version is easier to understand, faster, doesn't leave need a temp file and also, as a bonus, normalizes the audio to prevent clipping and not hurt my ears.

Using Sansa Clip+ MP3 Player for Podcasts

A mini-review after buying the 2GB model to replace my old mp3 player. I'll only consider it for the purpose of listening to podcasts, other music related features can be found on the SanDisk site or other reviews easily enough.

3 key features for listening to podcasts:

  • No software required, just plug in as a USB drive and copy files across (using a script or manually.)
  • Ability to easily delete files from the player after listening to them.
  • Increase the tempo/speed of playback.

The Sansa Clip+ does all of these, however the fast playback speed is pretty useless as the pitch is increased giving "chipmunk" effects. See the next post for a work-around.

The player remembers the position in each track, which is very nice.

A couple of other issues I've noticed immediately are that it is very small, making one-handed operation difficult, and it has no "hold" button to prevent inadvertent bumping of the buttons. Hopefully being able to clip it outside clothing/bags will alleviate this, time will tell.

It also has a built in battery so you can't carry a spare and must plug it in to charge.

Update: So far, everything is working well. I'm not used to the built in battery, and waiting for it to recharge if I let it go flat is a major pain, but I'll just have to keep it topped up and an hour of charging goes a long way.

One other minor annoyance is that you can't quickly see the duration of a podcast when skipping through them.

Update: One issue that I initially didn't notice, as the ID3 tags were stripped during my reencode process, is that the podcasts are organised by show and there is no "play all" option. This is a pain, I'm used to just listening to them in a more or less random order and not having to stop and select a new show when one finishes.

To quickly fix this, use the id3v2 utility to delete all ID3 tags from the podcast before copying them to the player. This way they are all categorised under a single "Unknown" show menu and the filename is usually sufficient to identify the program.