Help:why use 264 encode, The target file is larger than the original file

[cscxk]

source file is 278MB, target file is 387MB
encoding para is:CRF 18, keyint-min=4:--bframes=3:qpmax=51:merange=24:direct=auto:ref=5:analyse=all:level=4.1:keyint=240:qpmin=10:b-adapt=2:rc-lookahead=60:trellis=2: open-gop=1:vbv-bufsize=62500:me=umh:colorprim=film:transfer=bt709:colormatrix=bt709:cpu-independent=1:deblock=-1,-1: psy-rd=1,0.15:vbv-maxrate=50000


the source is VC1, eg:
Format : VC-1
Format profile : MP@HL
Codec ID : WMV3
Codec ID/Info : Windows Media Video 9
Codec ID/Hint : WMV3
Description of the codec : Windows Media Video 9 - Professional
Duration : 9m23s
Bit rate mode : VBR
Bit rate : 4 000 Kbps
Width : 1 280
Height : 720
Display aspect ratio : 16:9
Frame rate : 29.970 (29970/1000) fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8bit

and the target is :
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4.1
Format settings, CABAC : Yes
Format settings, ReFrames : 5 frames
Codec ID : V_MPEG4/ISO/AVC
Duration : 9mn 22s
Width : 1 280 pixels
Height : 720 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 29.970 (30000/1001) fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Writing library : x264 core 148 r2665 a01e339
Encoding settings : cabac=1 / ref=5 / deblock=1:-1:-1 / analyse=0x3:0x133 / me=umh / subme=7 / psy=1 / psy_rd=1.00:0.15 / mixed_ref=1 / me_range=24 / chroma_me=1 / trellis=2 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-3 / threads=6 / lookahead_threads=1 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=2 / b_bias=0 / direct=3 / weightb=1 / open_gop=1 / weightp=2 / keyint=240 / keyint_min=4 / scenecut=40 / intra_refresh=0 / rc_lookahead=60 / rc=crf / mbtree=1 / crf=18.0 / qcomp=0.60 / qpmin=10 / qpmax=51 / qpstep=4 / vbv_maxrate=50000 / vbv_bufsize=62500 / crf_max=0.0 / nal_hrd=none / filler=0 / ip_ratio=1.40 / aq=1:1.00
Default : Yes
Forced : No
Color range : Limited
Color primaries : Generic film
Transfer characteristics : BT.709
Matrix coefficients : BT.709

[raffriff42]

CRF 18,That's very high quality, much more than you need for a source encoded at 4 000 Kbps. Try CRF 24 or higher (higher CRF = smaller file, lower quality) or fixed bitrate. Re-encoding such a low bitrate source at a new low bitrate is gonna look pretty terrible though: I advise against it.

[cscxk]

That's very high quality, much more than you need for a source encoded at 4 000 Kbps. Try CRF 24 or higher (higher CRF = smaller file, lower quality) or fixed bitrate. Re-encoding such a low bitrate source at a new low bitrate is gonna look pretty terrible though: I advise against it.
I know crf 18 is very high quality, and more crf big more smaller file.
I use crf 18 want to save all infomation in source. I think if source is lower quality, crf 18 will be lower quality, but filesize will be smaller than source filesize. but it is not

[Groucho2004]

I know crf 18 is very high quality
That depends on who you ask, what equipment they have to judge quality, etc. Some consider CRF22 high quality, others won't go above CRF14.

I use crf 18 want to save all infomation in source. I think if source is lower quality, crf 18 will be lower quality, but filesize will be smaller than source filesize. but it is not
The file size (bitrate) at a given CRF value depends entirely on the source material. You can have an animation source that requires for example 1Mbps or you have a movie with lots of grain and/or action scenes and the required bitrate for the same CRF will be 10Mbps.

[StainlessS]

Your low quality source when compressed, and decompressed has additional artifacts that were not in the original (due to the compression).
When you try to re-compress again with high quality crf, its not going to get even smaller, its going to get bigger because it sees the
additional artifacts/noise as additional detail (over and above what was in original pre-compressed source), and because you select
high quality crf, is doing its best to keep intact all of the extra artifacts/noise.

[cscxk]

Your low quality source when compressed, and decompressed has additional artifacts that were not in the original (due to the compression).
When you try to re-compress again with high quality crf, its not going to get even smaller, its going to get bigger because it sees the
additional artifacts/noise as additional detail (over and above what was in original pre-compressed source), and because you select
high quality crf, is doing its best to keep intact all of the extra artifacts/noise.

maybe, you are right

[kypec]

maybe, you are right

Not "maybe" but "for sure" he is right. Anyway, if you want to keep the quality but do not want to accept bigger filesize why bother with re-encoding at all? :confused: Just play the original video file and you're done.