path: root/DOCS/tech/libavc-options.txt

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 (default)
	3 is recommended for h263(p)/msmpeg4
	   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
	31 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)
	0-2 is a sane range for mpeg4

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)
        for strict mpeg1/2/4 compliance this would have to be <=132

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)
        Tip: u can try to use constant quantizer mode for pass1 (vqscale=<quantizer>)
        for huffyuv:
        	pass 1 saves statistics
                pass 2 encodes with a optimal huffman table based upon the pass 1 stats

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

vrc_maxrate (maximum bitrate in kbit/sec) for pass1/2
vrc_minrate (minimum bitrate in kbit/sec) for pass1/2
vrc_buf_size (buffer size    in kbit) for pass1/2
	this is for stuff like VCD
	VCD:  FIXME
	SVCD: ...
	DVD:  ...
	Note: vratetol should not be too large during the 2.pass or there might 
              be problems if vrc_(min|max)rate is used

vb_qfactor (-31.0-31.0) for pass1/2
	1.25 is default
vi_qfactor (-31.0-31.0) for pass1/2
	0.8 is default
vb_qoffset (-31.0-31.0) for pass1/2
	1.25 is default
vi_qoffset (-31.0-31.0) for pass1/2
	0.0 is default
        if v{b|i}_qfactor > 0  
            I/B-Frame quantizer = P-Frame quantizer * v{b|i}_qfactor + v{b|i}_qoffset
        else    
            do normal ratecontrol (dont lock to next P frame quantizer) and
            set q= -q * v{b|i}_qfactor + v{b|i}_qoffset
	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 (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
vqblur (0.0-99.0) quantizer blur (pass2)
	gaussian blur (gaussian blur cant be done during pass 1 as the future quantizers arent known)
	0.5 is the default
	larger values will average the quantizer more over time so that it will
        be changed slower

vqcomp  quantizer compression (for pass1/2) 
	depends upon vrc_eq

vrc_eq	the main ratecontrol equation (for pass1/2)
	1			constant bitrate
	tex			constant quality
	1+(tex/avgTex-1)*qComp	approximately the equation of the old ratecontrol code
	tex^qComp		with qcomp 0.5 or something like that (default)

        infix operators: +,-,*,/,^
        variables:
		tex		texture complexity
		iTex,pTex	intra, non intra texture complexity
		avgTex		average texture complexity
		avgIITex	average intra texture complexity in I frames
		avgPITex	average intra texture complexity in P frames
		avgPPTex	average non intra texture complexity in P frames
		avgBPTex	average non intra texture complexity in B frames
		mv		bits used for MVs
		fCode		maximum length of MV in log2 scale
		iCount		number of intra MBs / number of MBs
		var		spatial complexity
		mcVar		temporal complexity
		qComp		qcomp from the command line
		isI, isP, isB	is 1 if picture type is I/P/B else 0
		Pi,E		see ur favorite math book

        functions: 
		max(a,b),min(a,b)	maximum / minimum
		gt(a,b)			is 1 if a>b, 0 otherwise
		lt(a,b)			is 1 if a<b, 0 otherwise
		eq(a,b)			is 1 if a==b,0 otherwise
		sin,cos,tan,sinh,cosh,tanh,exp,log,abs

vrc_override	user specified quality for specific parts (ending credits ...) (for pass1/2)
	<start-frame>,<end-frame>,<quality>[/<start-frame>,<end-frame>,<quality>[/...]]
	quality 2..31 -> quantizer
	quality -500..0 -> quality correcture in %
        
vrc_init_cplx	(0-1000) initial complexity for pass1

vqsquish (0 or 1) for pass1/2 how to keep the quantizer between qmin & qmax
	0 use cliping
	1 use a nice differentiable function (default)

vlelim (-1000-1000) single coefficient elimination threshold for luminance
	0 disabled (default)
	-4 (JVT recommendation)
	negative values will allso consider the dc coefficient
	should be at least -4 or lower for encoding at quant=1

vcelim (-1000-1000) single coefficient elimination threshold for chrominance
	0 disabled (default)
	7 (JVT recommendation)
	negative values will allso consider the dc coefficient
	should be at least -4 or lower for encoding at quant=1

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
	each videopacket will be encoded in 3 seperate partitions:
		1. MVs             (=movement)
		2. DC coefficients (=low res picture)
		3. AC coefficients (=details)
	the MV & DC are most important, loosing them looks far worse than 
	loosing the AC and the 1. & 2. partition (MV&DC) are far smaller than
	the 3. partition (AC) -> errors will hit the AC partition much more
	often than the MV&DC -> the picture will look better with partitioning
	than without, as without partitining an error will trash AC/DC/MV 
	equally
	improves error-resistance when transfering over unreliable channels (eg.
        streaming over the internet)

vpsize	(0-10000) video packet size
	0 disabled (default)
	100-1000 good choice
	improves error-resistance (see vdpart for more info)

gray	grayscale only encoding (a bit faster than with color ...)

vfdct	(0-99) dct algorithm
	0 automatically select a good one (default)
	1 fast integer 
        2 accurate integer
        3 mmx
        4 mlib
        
idct	(0-99) idct algorithm
	0 automatically select a good one (default)
	1 jpeg reference integer
        2 simple
        3 simplemmx
        4 libmpeg2mmx (inaccurate, DONT USE for encoding with keyint >100)
        5 ps2
        6 mlib
        7 arm
        note: all these IDCTs do pass the IEEE1180 tests AFAIK

lumi_mask	(0.0-1.0) luminance masking
	0.0 disabled (default)
        0.0-0.3 should be a sane range
        warning: be carefull, too large values can cause disasterous things
        warning2: large values might look good on some monitors but may look horrible
        on other monitors

dark_mask	(0.0-1.0) darkness masking
	0.0 disabled (default)
        0.0-0.3 should be a sane range
        warning: be carefull, too large values can cause disasterous things
        warning2: large values might look good on some monitors but may look horrible
        on other monitors / TV / TFT
        
tcplx_mask	(0.0-1.0) temporal complexity masking
	0.0 disabled (default)

scplx_mask	(0.0-1.0) spatial complexity masking
	0.0 disabled (default)
        0.0-0.5 should be a sane range
        larger values help against blockiness, if no deblocking filter is used
        for decoding
        Tip: crop any black borders completly away as they will reduce the quality
        of the MBs there, this is true if scplx_mask isnt used at all too

naq	normalize adaptive quantization
	experimental
 
ildct	use interlaced dct

format
	YV12 (default)
        422P (for huffyuv)

pred (for huffyuv)
	0 left prediction
        1 plane/gradient prediction
        2 median prediction

lavdopts: (decoder options)
---------------------------

ec	error concealment
	1 use strong deblock filter for damaged MBs
        2 iterative MV search (slow)
        3 all (default)
        Note: just add the ones u want to enable

er	error resilience
	0 disabled
        1 carefull (should work with broken encoders)
        2 normal (default) (works with compliant encoders)
        3 agressive (more checks but might cause problems even for valid bitstreams)
        4 very agressive

bug	manual workaround encoder bugs (autodetection isnt foolproof for these)
	0 nothing
	1		autodetect bugs (default)
	2 for msmpeg4v3	some old lavc generated msmpeg4v3 files (no autodetect)
	4 for mpeg4	xvid interlacing bug     (autodetected if fourcc==XVIX)
	8 for mpeg4	UMP4                     (autodetected if fourcc==UMP4)
        16for mpeg4	padding bug
        32for mpeg4	illegal vlc bug          (autodetected per fourcc)
	64for mpeg4	XVID&DIVX qpel bug	 (autodetected)
        Note: just add the ones u want to enable

gray	grayscale only decoding (a bit faster than with color ...)

idct	see lavcopts
        note: the decoding quality is highest if the same idct algorithm is used 
        for decoding as for encoding, this is often not the most accurate though


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 use data partitioning or increase 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
RC	Rate control
DCT	Discrete Cosine Transform
IDCT	Inverse Discrete Cosine Transform
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

Links:
short intro to mpeg coding:
http://www.eecs.umich.edu/~amarathe/mpeg.html
longer intro to jpeg/mpeg coding:
http://www.cs.sfu.ca/undergrad/CourseMaterials/CMPT479/material/notes/Chap4/Chap4.2/Chap4.2.html

--
Written 2002 by Michael Niedermayer and reviewed by Felix Buenemann.
Check the MPlayer documentation for contact-addresses.