Here's what I need to do: convert a 30.0 sec WAV to a 30.0 MP3.
I've tried doing this using LAME however no matter what I try LAME always adds a short moment of silence to the output mp3. Using LAME my 30.0 sec WAV becomes a 30.1 sec MP3. That's lame.
Does anyone know of a way to convert WAV to MP3 using the Windows command line?
For example by running program.exe in.wav out.mp3 from CMD?
It is critical that NO silence is added to the resulting MP3 file. I can't stress that enough.
An MP3 stream contains info for generating a set of samples where each sample corresponds to a sample in the original LPCM data (like from the WAV file), but a side-effect of encoding is that there is some extra "junk" added to each end, and a side-effect of decoding is that there is even more junk added to the beginning. The decoder will know how much it adds and will skip those samples, but the encoder-added junk isn't entirely predictable (different encoders add different amounts), so the decoder can't skip those samples unless it is somehow informed of what to skip. Some encoders, like LAME, will add such "gapless playback" or "delay and padding" info (in an encoder-specific format, because there's no standard for it) into the file's VBR Info (VBRI) or Xing header, which is sort-of standard even on CBR files, and which contains other info that is sometimes helpful to the player. This header is actually a frame of silence (usually 1152 samples) with some specially formatted info embedded in between the frame's header and the start of its null audio data. Most decoders/players recognize the frame as special and skip those samples, but some don't, so there's another potential point of failure. so I would look toward making sure you use a compatible encoder/decoder combo to get correct-length, junk-trimmed files as output.
Your second question...did you notice the LAME command-line app's "--decode" option? :) This should solve your problem if you're using LAME as the encoder. The output length should match the input.
I want to add this FAQ and a superuser thread to the discussion:
just search for online audio converters, they are totally free, I use this one called DumpMedia Video Converter it can not only convert audio but also video files. And it has an online and offline version, you can't convert in batch using online tools, so you can use this one to convert your playlist at once.
I don't know how and why, but ffmpeg -i q.wav q.mp3; ffmpeg -i q.mp3 q2.wav preserve file length for me. And looks like it don't add silence in the begining of file.
I want to provide a somewhat more concise and clearer answer.
I'm afraid there is no way to create MP3 files that consistently play back without gaps at the start and end. This is known as Gapless Playback and is a much discussed problem.
As at least one of the other answers says, there are workarounds that work with some specific music players.
