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LAME MP3 encoding starts fast then slows down
Kaze3
post Apr 27 2012, 10:17
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Hi all.

I've been converting some FLAC files to MP3 using foobar and LAME 3.99.5 (64-bit). I find that the encoding starts at ~220x with 100% CPU usage, but after a short time (varies) it drops to ~60-80x with the CPU usage dropping significantly as well. I'm wondering if I'm being limited by the hard disk speed - I've tried converting with the source and destination on the same drive, and also the source on the HDD and the destination on my SSD drive and I see the same behaviour with both. I've also tried the 32-bit LAME encoder and the one that's built-in to foobar (same behaviour).

Can anyone suggest whether something's going wrong of if I am indeed limited by my hardware (HDD or otherwise)? Thanks.
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skamp
post Jun 13 2012, 09:29
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QUOTE (dumdidum @ Jun 12 2012, 23:40) *
are decoders and encoders really that fast so that disk access becomes the bottle neck?


The faster the CPU, the faster the codec, and the slower the HDD, the more of a bottleneck the latter will be. Encoding WAV files to FLAC at the default compression level on my machine shows a substantial difference in encoding time when caching the input files sequentially (see here).

The smaller size of FLACs compared to WAV (less reading), and the relatively slow encoding speed of LAME, mitigate the need for fast I/O, though the end result depends entirely on your hardware (and software) configuration. Caching input files sequentially is still beneficial in most cases where a (slowish) HDD is involved.

lvqcl also mentionned this related thread.

QUOTE (saratoga @ Jun 13 2012, 03:26) *
So basically, you're saying that its 220x is across all 4 CPUs?


That sounds about right: I get about 185x when encoding WAVs from a ramdisk to LAME --preset standard on my 2.2 GHz Core i7 (8 threads).


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See my profile for measurements, tools and recommendations.
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Posts in this topic
- Kaze3   LAME MP3 encoding starts fast then slows down   Apr 27 2012, 10:17
- - megar   Audio encoding is not very well suited for multi-t...   Apr 27 2012, 12:04
|- - Kaze3   Sorry I haven't replied for so long. I'm s...   Jun 12 2012, 19:42
- - Ouroboros   It's highly likely to be limited by disk I/O, ...   Jun 12 2012, 20:05
|- - dumdidum   QUOTE (Ouroboros @ Jun 12 2012, 21:05) It...   Jun 12 2012, 22:40
|- - Ouroboros   QUOTE (dumdidum @ Jun 12 2012, 22:40) I...   Jun 12 2012, 23:16
||- - dumdidum   QUOTE (Ouroboros @ Jun 13 2012, 00:16) QU...   Jun 12 2012, 23:37
||- - Ouroboros   QUOTE (dumdidum @ Jun 12 2012, 23:37) the...   Jun 13 2012, 00:02
||- - washu   QUOTE (dumdidum @ Jun 12 2012, 18:37) the...   Jun 13 2012, 01:05
|- - saratoga   QUOTE (dumdidum @ Jun 12 2012, 17:40) QUO...   Jun 12 2012, 23:26
|- - dumdidum   QUOTE (saratoga @ Jun 13 2012, 00:26) 4*2...   Jun 13 2012, 00:04
|- - saratoga   QUOTE (dumdidum @ Jun 12 2012, 19:04) QUO...   Jun 13 2012, 00:54
- - washu   Try running a test conversion with both the source...   Jun 12 2012, 20:24
- - probedb   It's also not necessarily true that running an...   Jun 12 2012, 21:56
- - pdq   The input file is much larger than the output, so ...   Jun 12 2012, 22:29
- - dumdidum   QUOTE (saratoga @ Jun 13 2012, 00:26) 4*2...   Jun 13 2012, 01:06
|- - saratoga   QUOTE (dumdidum @ Jun 12 2012, 20:06) so ...   Jun 13 2012, 02:26
|- - dumdidum   QUOTE (saratoga @ Jun 13 2012, 03:26) So ...   Jun 13 2012, 08:42
- - skamp   QUOTE (dumdidum @ Jun 12 2012, 23:40) are...   Jun 13 2012, 09:29


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