FFMPEG Bitrate specification

[adhawkins]

Hi all,

I'm trying to convert an M2T file, specifying bit rates during the conversion. I'm using the following FFMPEG command line (under windows):

ffmpeg -y -threads 2 -i "nature.m2t" -vcodec libx264 -fpre "test.ffpreset" -bufsize 600 -maxrate 20000 -b 10000 -acodec mp2 -ac 2 -ar 48000 -ab 160k -f mpegts -metadata service_provider="OurCo" "nature-bitrate-10000.m2t"

The contents of test.ffpreset is below:

coder=0
flags=+loop
cmp=+chroma
partitions=+parti8x8+parti4x4+partp8x8+partb8x8
me_method=epzs
subq=5
me_range=16
g=100
keyint_min=25 
sc_threshold=40
i_qfactor=0.71
b_strategy=1
qcomp=0.6
qmin=10
qmax=30
qdiff=4
bf=16
refs=2
directpred=3
trellis=0
flags2=+bpyramid+wpred+dct8x8+fastpskip

However, I get the following message during the conversion:

[libx264 @ 01EC0B20] VBV maxrate specified, but no bufsize, ignored

This is the ffmpeg version information:

ffmpeg version git-N-30344-g5501afa, Copyright (c) 2000-2011 the FFmpeg developers
  built on May 27 2011 22:37:57 with gcc 4.5.3
  configuration: --enable-gpl --enable-version3 --enable-memalign-hack --enable-runtime-cpudetect --enable-avisynth --enable-bzlib --enable-frei0r --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libfreetype --enable-libgsm --enable-libmp3lame --enable-libopenjpeg --enable-librtmp --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxavs --enable-libxvid --enable-zlib --pkg-config=pkg-config

Can anyone offer any suggestions as to when it's saying I'm not specifying bufsize, when in fact I am?

Thanks

Andy

[Chris K]

Set buffersize to 600k.

Also check out bitrate and maxrate. Shouldn't that be -b 1000k and -maxrate 2000k?

[adhawkins]

I figured it would probably be something simple!

Now seeing:

[libx264 @ 01FF28E0] VBV buffer size cannot be smaller than one frame, using 800 kbit

I'm calculating the buffer size as bitrate * 3 / FPS (10000 * 3 / 50 = 600) based on advice at https://trac.handbrake.fr/wiki/VBVRateControl. Why does it think it needs to be bigger?

Thanks for the pointer so far!

Andy

[Chris K]

10000 is a bitrate of 10 kbps for FFmpeg which seems rather unrealistic for me, even for x264.

[adhawkins]

Ok, but same applies for 2000 and 5000. I get a similar error saying that the buffer size is smaller than a frame. These are all 'k' obviously (10000k, 5000k and 2000k). And the buffer size I'm specifying for 10000k is 600k, but it says that's too small and uses 800k.

Andy