Error on avconv 2-pass

**johny why** · September 5th, 2015

with 2-pass, i'm getting:

$ avconv -i run.mp4 -pass 1 -vn -y -passlogfile run.log /dev/null
avconv version 9.18-6:9.18-0ubuntu0.14.04.1, Copyright (c) 2000-2014 the Libav developers
built on Mar 16 2015 13:19:10 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'run.mp4':
Metadata:
major_brand : mp42
minor_version : 0
compatible_brands: isommp42
creation_time : 2015-02-07 18:18:58
Duration: 00:06:02.11, start: 0.000000, bitrate: 656 kb/s
Stream #0.0(und): Video: h264 (High), yuv420p, 1280x720 [PAR 1:1 DAR 16:9], 462 kb/s, 29.97 fps, 29.97 tbr, 30k tbn, 59.94 tbc
Stream #0.1(und): Audio: aac, 44100 Hz, stereo, fltp, 191 kb/s
Metadata:
creation_time : 2015-02-07 18:18:59
Unable to find a suitable output format for '/dev/null'

thx for any help.

**TheFu** · September 5th, 2015

Don't use 2-pass encoding. I stopped using it about 3 yrs ago when h.264 become easily available. Do you need xvid or mpeg2v4 output?

Use "constant quality" encoding for better results.

Also, use ffmpeg, not avconv. Things like this tend to work better with ffmpeg; don't know why. Yesterday, I posted a conversion script in these forums. Should be easy to find and tweak for your needs. Quality values of 19 are insanely great. 19.5 doesn't show any artifacts, but 20 begins to for high-action scenes. You can also control the file compression levels using presets in ffmpeg. This impacts transcoding fps more than anything else, IME.

Code:

 FF_OPTS="-vcodec libx264 -crf 19 -vf scale=-1:720 -preset medium -strict experimental -c:a aac "
nice ffmpeg -y -i file-in.mpeg2 $FF_OPTS  file-out.mkv

You get the idea.

**johny why** · September 5th, 2015

thx, but this is for conversion to audio-only mp3, so i think your suggestions about video would not apply. Is h.264 for audio mp3's?

**TheFu** · September 5th, 2015

I'd use mplayer for that - not a 2-pass video encoding. Is there a specific reason for the 2-pass video?

Something like ...

Code:

#!/bin/bash
nice mplayer -ao pcm:waveheader -vc null -vo null $1 -ao pcm:fast:file=$1.wav
nice lame --preset mw-us $1.wav
rm $1.wav

Haven't used in this in awhile. Or something like ....

I suspect ffmpeg -i file.mp4 file.mp3 would do what you want.

**johny why** · September 6th, 2015

my understanding is that the 2-pass process optimizes the conversion, re size and quality.

is that incorrect?

**mc4man** · September 6th, 2015

Then copy the audio only out to a file & do as you please converting to mp3
(I think very few see value in 2 pass mp3 encoding, do a web search
1 ex. http://www.hydrogenaud.io/forums/ind...howtopic=49127