[FFmpeg-devel] parameter ranges bug / minrate q

[Michael Niedermayer]

On Thu, Jul 17, 2008 at 09:29:16AM -0700, tripp wrote:
> hi,
> 
> 1. i'd like to ask the exact meaning of this:
> [mpeg4 @ 00AD0900]Warning min_rate > 0 but min_rate != max_rate 
> isn't recommended!

The exact meaning is that it is not recommanded to
set min_rate > 0 when min_rate != max_rate.


> 
> i asked over a week ago on ffmpeg-user.
> at first i'd thought i didn't pad the bitsream 
> like other encoders, with a minrate setting,
> but it seems to do so,
> 
> so i assume that there's the recommendation because,
> setting -minrate != -maxrate ratecontrol is unable to meet target bitrate?
> and currently -minrate is only useful in setting cbr encodes,
> with minrate=maxrate?
> if so is it to change?

interresting speculations
Now while i do not exactly remember why this was added originally 
i do not think it means much more now than that min_rate>0 is a waste of bits.


> a word in the docs would be nice.

send a patch


> 
> 
> 2. values of 0 for:
> qblur
> qcomp
> b_qoffset
> 
> return errors like so:
> ffmpeg143 -i input.avi -b 700k -qcomp 0 -an -y out.mp4
> FFmpeg version SVN-r14236, Copyright (c) 2000-2008 Fabrice Bellard, et al.
>   configuration: --enable-memalign-hack --enable-postproc --enable-swscale --ena
> ble-gpl --enable-libfaac --enable-libfaad --enable-libgsm --enable-libmp3lame --
> enable-libvorbis --enable-libtheora --enable-libx264 --enable-libxvid --disable-
> ffserver --disable-vhook --enable-avisynth --enable-pthreads
>   libavutil version: 49.7.0
>   libavcodec version: 51.60.0
>   libavformat version: 52.17.0
>   libavdevice version: 52.0.0
>   built on Jul 15 2008 19:35:58, gcc: 4.2.4 (TDM-1 for MinGW)
> 
> Seems stream 0 codec frame rate differs from container frame rate: 23.98 (65535/
> 2733) -> 23.98 (24000/1001)
> Input #0, avi, from 'input.avi':
>   Duration: 00:00:41.71, start: 0.000000, bitrate: 689 kb/s
>     Stream #0.0: Video: mpeg4, yuv420p, 624x352 [PAR 1:1 DAR 39:22], 23.98 tb(r)
> 
>     Stream #0.1: Audio: mp3, 44100 Hz, stereo, 112 kb/s
> Value 0.000000 for parameter 'qcomp' out of range.
> Value 0.000000 for parameter 'qcomp' out of range.
> Value 0.000000 for parameter 'qcomp' out of range.
> ffmpeg143: unrecognized option '-qcomp'

fixed


[...]
> 3. speaking of,
> setting -rc_eq "1" does not deliver a cbr encode
> nor does -rc_eq "tex" do the opposite from what i gather.

yes, this is correct.

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The greatest way to live with honor in this world is to be what we pretend
to be. -- Socrates
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