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Description of what all those libavcodec options do ...
WARNING: I am no encoding expert so the recommendations might be bad ...
if you find any errors, missing stuff, ... send a patch or cvs commit if you
have an cvs account :)
lavcopts: (encoder options)
---------------------------
vqmin 2-31 (minimum quantizer) for pass1/2
1 is not recommended (much larger file, little quality difference (if u are lucky)
and other weird things (if u are less lucky))
weird things: msmpeg4, h263 will be very low quality
ratecontrol will be confused -> lower quality
some decoders will not be able to decode it
2 is recommended for normal mpeg4/mpeg1video encoding
3 is recommended for h263(p)/msmpeg4 (default)
the reason for 3 instead of 2 is that 2 could lead to overflows
(this will be fixed for h263(p) by changing the quanizer per MB in
the future, but msmpeg4 doesnt support that so it cant be fixed for
that)
vqscale 1-31 quantizer for constant quantizer / constant quality encoding
1 is not recommended (much larger file, little quality difference and
possible other weird things)
lower means better quality but larger files
see vqmin
vqmax 1-31 (maximum quantizer) for pass1/2
15 default
10-31 should be a sane range
vqdiff 1-31 (maximum quantizer difference between I or P frames) for pass1/2
3 default
vmax_b_frames 0-4 (maximum number of B frames between non B frames)
0 no b frames (default)
vme 0-5 (motion estimation)
0 none (not recommanded, very lq)
1 full (not recommanded, too slow)
2 log (not recommanded, lq)
3 phods (not recommanded, lq)
4 EPZS (default)
5 X1
vhq (high quality mode)
encode each MB as in all modes and choose the best (this is slow but
better filesize/quality)
disabled by default
v4mv
allow 4 MV per MB (little difference in filesize/quality)
disabled by default
cannot be used with B frames (should now work in lq mode)
keyint 0-300 (maximum interval between keyframes)
keyframes are needed for seeking as seeking is only possible to a
keyframe but they need more space than non-keyframes so larger numbers here
mean slightly smaller files, but less precise seeking
0 no keyframes
>300 is not recommended as the quality might be bad (depends upon
decoder, encoder and luck)
vb_strategy 0-1 for pass 2
0 allways use the max number of B frames (default)
1 avoid B frames in high motion scenes (this will cause bitrate
misprediction)
vpass
1 first pass
2 second pass
(only need to specify if two-pass encoding is used)
vbitrate (kbits per second) for pass1/2
800 is default
(if value is bigger then 16000 it is interpreted as bit not kbit!)
vratetol (filesize tolerance in kbit) for pass1/2
this is just an approximation, the real difference can be much smaller
or larger
1000-100000 is a sane range
8000 is default
vb_qfactor (1.0-31.0) for pass1/2
(B-Frame quantizer = IP-Frame quantizer * vb_qfactor)
2.0 is default
tip: to do constant quantizer encoding with different quantizers for
I/P and B frames you can use:
vqmin=<ip_quant>:vqmax=<ip_quant>:vb_qfactor=<b_quant/ip_quant>
vqblur (0.0-1.0) quantizer blur (only for pass1)
0.0 qblur disabled
0.5 is the default
1.0 average the quantizer over all previous frames
larger values will average the quantizer more over time so that it will
be changed slower
vqcomp (0.0-1.0) quantizer compression (for pass1/2)
0.0 constant bitrate encoding, so fast motion frames will get as many
bits as low motion (high motion scenes look bad)
0.5 (default)
1.0 constant quantizer encoding (low motion scenes look bad)
vrc_strategy (0,1,2)
FIXME (different rate control strategies)
vlelim (0-1000) single coefficient elimination threshold for luminance
0 disabled (default)
4 (JVT recommendation)
vcelim (0-1000) single coefficient elimination threshold for chrominance
0 disabled (default)
7 (JVT recommendation)
vstrict strict standard compliance
only recommended if you want to feed the output into the mpeg4 reference
decoder
vdpart data partitioning
adds 2 byte per video packet
improves error-resistance when transfering over unreliable channels (eg.
streaming over the internet)
vpsize (0-10000) video packet size
0 disabled (default)
500-1000 good choice
improves error-resistance (see vdpart for more info)
gray grayscale only encoding (a bit faster than with color ...)
lavdopts: (decoder options)
---------------------------
ver error resilience
-1 needed for some very broken, encoders which completly ignore the
standards (one M4S2 asf sample know to need this) (default)
0
1 more aggressive error detection, lavc might think that some correct
streams contain errors
bug manual workaround encoder bugs (cant be easily detected automatically)
0 (default)
1 for msmpeg4v3 workaround for some old lavc generated msmpeg4v3 files
1 for mpeg4 workaround some opendivx? files
see http://heroinewarrior.com for some samples
gray grayscale only decoding (a bit faster than with color ...)
Notes: 1. lavc will strictly follow the quantizer limits vqmin, vqmax, vqdiff
even if it violates the bitrate / bitrate tolerance
2. changing some options between pass1 & 2 can reduce the quality
FAQ: Q: Why is the filesize much too small?
A: Try to increase vqmin=2 or 1 (be carefull with 1, it could cause
strange things to happen).
Q: Can I use -pass 1 & -pass 2 with vmax_b_frames>0 ?
A: -pass x uses the divx4 twopass-encoding codem which is incompatible
with the libavcodec encode.
If you want to fix it read DOCS/tech/patches.txt and send a patch.
Q: What provides better error recovery while keeping the filesize low?
Should I increase data partitioning or the number of video packets?
A: Data partitioning is better in this case.
Glossary:
MB Macroblock (16x16 luminance and 8x8 chrominance samples)
MV Motion vector
ME Motion estimation
MC Motion compensation
JVT Joint Video Team Standard -- http://www.itu.int/ITU-T/news/jvtpro.html
Examples:
mencoder foobar.avi -lavcopts vcodec=mpeg4:vhq:keyint=300:vqscale=2 -o new-foobar.avi
mplayer foobar.avi -lavdopts bug=1
--
Written 2002 by Michael Niedermayer and reviewed by Felix Buenemann.
Check the MPlayer documentation for contact-addresses.
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