尝试压缩最后一点时，我发现我的文件先变大然后又变小。不幸的是，我一定是误解了一些参数。
也许你可以帮助我。
参考文献是-preset placebo：
ffmpeg -y -hide_banner -i <input.mp4> \
[... audio ...] \
-pix_fmt yuv420p \
-preset placebo \
-crf 30 \
-codec:v libx265 \
-f mp4 \
-movflags +faststart+disable_chpl \
<output.mp4>
生成的文件大小为 130.780.586 字节。
然后我读了文档并尝试理解参数的含义。
后来我用
ffmpeg -y -hide_banner -i <input.mp4> \
[... audio ...] \
-pix_fmt yuv420p \
-preset placebo \
-crf 30 \
-x265-params "ssim=0:psnr=0:frame-threads=1:pools=*:wpp=0:pmode=0:pme=0:slices=1:copy-pic=1:level-idc=0:high-tier=1:ref=6:allow-non-conformance=0:uhd-bd=0:rd=6:ctu=64:min-cu-size=8:limit-refs=0:limit-modes=0:rect=0:amp=0:early-skip=0:rskip=0:splitrd-skip=0:fast-intra=0:b-intra=1:cu-lossless=1:tskip-fast=0:rd-refine=1:rdoq-level=1:tu-intra-depth=4:tu-inter-depth=4:limit-tu=0:nr-intra=0:tskip=0:rdpenalty=0:max-tu-size=32:dynamic-rd=0:ssim-rd=1:max-merge=5:me=full:subme=7:merange=32767:temporal-mvp=1:weightp=1:weightb=1:analyze-src-pics=1:strong-intra-smoothing=1:constrained-intra=0:psy-rd=2.0:psy-rdoq=1.0:open-gop=1:keyint=15000:min-keyint=2:scenecut=40:scenecut-bias=5:ctu-info=0:intra-refresh=0:rc-lookahead=250:lookahead-slices=0:lookahead-threads=0:b-adapt=2:bframes=16:bframe-bias=0:b-pyramid=1:force-flush=0:crf-max=51.0:crf-min=0.0:vbv-bufsize=0:vbv-maxrate=0:vbv-init=0.0:vbv-end=0.0:vbv-end-fr-adj=0:lossless=0:aq-mode=3:aq-strength=1.0:aq-motion=1:qg-size=8:cutree=1:strict-cbr=0:signhide=1:sao=1:sao-non-deblock=0:limit-sao=0:opt-qp-pps=1:opt-ref-list-length-pps=1:opt-cu-delta-qp=1" \
-codec:v libx265 \
-f mp4 \
-movflags +faststart+disable_chpl \
<output.mp4>
生成的文件大小为 300.468.224 字节。
显然视觉质量更好。但我认为它应该是恒定的，因为-crf 30。我是否必须通过增加来降低可变比特率-crf？
为了更好的可读性，再次说明参数：
-x265-params "
ssim=0:
psnr=0:
frame-threads=1:
pools=*:
wpp=0:
pmode=0:
pme=0:
slices=1:
copy-pic=1:
level-idc=0:
high-tier=1:
ref=6:
allow-non-conformance=0:
uhd-bd=0:
rd=6:
ctu=64:
min-cu-size=8:
limit-refs=0:
limit-modes=0:
rect=0:amp=0:
early-skip=0:
rskip=0:
splitrd-skip=0:
fast-intra=0:
b-intra=1:
cu-lossless=1:
tskip-fast=0:
rd-refine=1:
rdoq-level=1:
tu-intra-depth=4:
tu-inter-depth=4:
limit-tu=0:
nr-intra=0:
tskip=0:
rdpenalty=0:
max-tu-size=32:
dynamic-rd=0:
ssim-rd=1:
max-merge=5:
me=full:
subme=7:
merange=32767:
temporal-mvp=1:
weightp=1:
weightb=1:
analyze-src-pics=1:
strong-intra-smoothing=1:
constrained-intra=0:
psy-rd=2.0:
psy-rdoq=1.0:
open-gop=1:
keyint=15000:
min-keyint=2:
scenecut=40:
scenecut-bias=5:
ctu-info=0:
intra-refresh=0:
rc-lookahead=250:
lookahead-slices=0:
lookahead-threads=0:
b-adapt=2:
bframes=16:
bframe-bias=0:
b-pyramid=1:
force-flush=0:
crf-max=51.0:
crf-min=0.0:
vbv-bufsize=0:
vbv-maxrate=0:
vbv-init=0.0:
vbv-end=0.0:
vbv-end-fr-adj=0:
lossless=0:
aq-mode=3:
aq-strength=1.0:
aq-motion=1:
qg-size=8:
cutree=1:
strict-cbr=0:
signhide=1:
sao=1:
sao-non-deblock=0:
limit-sao=0:
opt-qp-pps=1:
opt-ref-list-length-pps=1:
opt-cu-delta-qp=1"
运行的输出placebo：
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '<input.mp4>':
Metadata:
major_brand : mp42
minor_version : 0
compatible_brands: mp42mp41
creation_time : 2018-03-25T07:58:52.000000Z
Duration: 00:07:03.46, start: 0.000000, bitrate: 207200 kb/s
Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1920x1080 [SAR 1:1 DAR 16:9], 207062 kb/s, 24 fps, 24 tbr, 24k tbn, 48 tbc (default)
Metadata:
creation_time : 2018-03-25T07:58:52.000000Z
handler_name : ?Mainconcept Video Media Handler
encoder : AVC Coding
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 157 kb/s (default)
Metadata:
creation_time : 2018-03-25T07:58:52.000000Z
handler_name : #Mainconcept MP4 Sound Media Handler
Stream mapping:
Stream #0:0 -> #0:0 (h264 (native) -> hevc (libx265))
Stream #0:1 -> #0:1 (aac (native) -> aac (native))
Press [q] to stop, [?] for help
x265 [info]: HEVC encoder version 2.6
x265 [info]: build info [Linux][GCC 7.2.0][64 bit] 8bit+10bit+12bit
x265 [info]: using cpu capabilities: MMX2 SSE2Fast LZCNT SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
x265 [info]: Main profile, Level-4 (Main tier)
x265 [info]: Thread pool created using 8 threads
x265 [info]: Slices : 1
x265 [info]: frame threads / pool features : 3 / wpp(17 rows)
x265 [info]: Coding QT: max CU size, min CU size : 64 / 8
x265 [info]: Residual QT: max TU size, max depth : 32 / 4 inter / 4 intra
x265 [info]: ME / range / subpel / merge : star / 92 / 5 / 5
x265 [info]: Keyframe min / max / scenecut / bias: 24 / 250 / 40 / 5.00
x265 [info]: Lookahead / bframes / badapt : 60 / 8 / 2
x265 [info]: b-pyramid / weightp / weightb : 1 / 1 / 1
x265 [info]: References / ref-limit cu / depth : 5 / off / off
x265 [info]: AQ: mode / str / qg-size / cu-tree : 1 / 1.0 / 32 / 1
x265 [info]: Rate Control / qCompress : CRF-30.0 / 0.60
x265 [info]: tools: rect amp rd=6 psy-rd=2.00 rdoq=2 psy-rdoq=1.00 tskip
x265 [info]: tools: signhide tmvp b-intra strong-intra-smoothing deblock sao
Output #0, mp4, to '<output.mp4>':
Metadata:
major_brand : mp42
minor_version : 0
compatible_brands: mp42mp41
encoder : Lavf57.83.100
Stream #0:0(eng): Video: hevc (libx265) (hev1 / 0x31766568), yuv420p(progressive), 1506x1080 [SAR 1:1 DAR 251:180], q=2-31, 24 fps, 12288 tbn, 24 tbc (default)
Metadata:
creation_time : 2018-03-25T07:58:52.000000Z
handler_name : ?Mainconcept Video Media Handler
encoder : Lavc57.107.100 libx265
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 48 kb/s (default)
Metadata:
creation_time : 2018-03-25T07:58:52.000000Z
handler_name : #Mainconcept MP4 Sound Media Handler
encoder : Lavc57.107.100 aac
[mp4 @ 0x558418671660] Starting second pass: moving the moov atom to the beginning of the file
frame=10162 fps=0.1 q=-0.0 Lsize= 127715kB time=00:07:03.43 bitrate=2470.8kbits/s speed=0.00405x
video:124915kB audio:2502kB subtitle:0kB other streams:0kB global headers:2kB muxing overhead: 0.233744%
x265 [info]: frame I: 58, Avg QP:32.08 kb/s: 3827.66
x265 [info]: frame P: 1838, Avg QP:33.65 kb/s: 3792.41
x265 [info]: frame B: 8266, Avg QP:36.26 kb/s: 2100.06
x265 [info]: Weighted P-Frames: Y:7.0% UV:7.0%
x265 [info]: Weighted B-Frames: Y:18.1% UV:17.6%
x265 [info]: consecutive B-frames: 4.7% 3.3% 11.0% 20.1% 16.9% 12.9% 10.2% 9.7% 11.2%
encoded 10162 frames in 104535.21s (0.10 fps), 2416.02 kb/s, Avg QP:35.76
[aac @ 0x5584186c0220] Qavg: 156.304
夸张运行的输出如下：
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '<input.mp4>':
Metadata:
major_brand : mp42
minor_version : 0
compatible_brands: mp42mp41
creation_time : 2018-03-25T07:58:52.000000Z
Duration: 00:07:03.46, start: 0.000000, bitrate: 207200 kb/s
Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1920x1080 [SAR 1:1 DAR 16:9], 207062 kb/s, 24 fps, 24 tbr, 24k tbn, 48 tbc (default)
Metadata:
creation_time : 2018-03-25T07:58:52.000000Z
handler_name : ?Mainconcept Video Media Handler
encoder : AVC Coding
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 157 kb/s (default)
Metadata:
creation_time : 2018-03-25T07:58:52.000000Z
handler_name : #Mainconcept MP4 Sound Media Handler
Stream mapping:
Stream #0:0 -> #0:0 (h264 (native) -> hevc (libx265))
Stream #0:1 -> #0:1 (aac (native) -> aac (native))
Press [q] to stop, [?] for help
x265 [info]: HEVC encoder version 2.6
x265 [info]: build info [Linux][GCC 7.2.0][64 bit] 8bit+10bit+12bit
x265 [info]: using cpu capabilities: MMX2 SSE2Fast LZCNT SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
x265 [info]: Main profile, Level-4 (Main tier)
x265 [info]: Slices : 1
x265 [info]: frame threads / pool features : 1 / none
x265 [info]: Coding QT: max CU size, min CU size : 64 / 8
x265 [info]: Residual QT: max TU size, max depth : 32 / 4 inter / 4 intra
x265 [info]: ME / range / subpel / merge : full / 32767 / 7 / 5
x265 [info]: Keyframe min / max / scenecut / bias: 2 / 15000 / 40 / 5.00
x265 [info]: Lookahead / bframes / badapt : 250 / 16 / 2
x265 [info]: b-pyramid / weightp / weightb : 1 / 1 / 1
x265 [info]: References / ref-limit cu / depth : 6 / off / off
x265 [info]: AQ: mode / str / qg-size / cu-tree : 3 / 1.0 / 8 / 1
x265 [info]: Rate Control / qCompress : CRF-30.0 / 0.60
x265 [info]: tools: rd=6 ssim-rd psy-rd=2.00 rdoq=1 psy-rdoq=1.00 rd-refine
x265 [info]: tools: cu-lossless signhide tmvp b-intra strong-intra-smoothing
x265 [info]: tools: deblock sao
Output #0, mp4, to '<output.mp4>':
Metadata:
major_brand : mp42
minor_version : 0
compatible_brands: mp42mp41
encoder : Lavf57.83.100
Stream #0:0(eng): Video: hevc (libx265) (hev1 / 0x31766568), yuv420p(progressive), 1506x1080 [SAR 1:1 DAR 251:180], q=2-31, 24 fps, 12288 tbn, 24 tbc (default)
Metadata:
creation_time : 2018-03-25T07:58:52.000000Z
handler_name : ?Mainconcept Video Media Handler
encoder : Lavc57.107.100 libx265
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 48 kb/s (default)
Metadata:
creation_time : 2018-03-25T07:58:52.000000Z
handler_name : #Mainconcept MP4 Sound Media Handler
encoder : Lavc57.107.100 aac
[mp4 @ 0x564f7705a760] Starting second pass: moving the moov atom to the beginning of the file
frame=10162 fps=0.1 q=-0.0 Lsize= 293426kB time=00:07:03.43 bitrate=5676.7kbits/s speed=0.00402x
video:290747kB audio:2502kB subtitle:0kB other streams:0kB global headers:2kB muxing overhead: 0.060220%
x265 [info]: frame I: 34, Avg QP:28.44 kb/s: 8462.33
x265 [info]: frame P: 1710, Avg QP:31.95 kb/s: 6614.87
x265 [info]: frame B: 8418, Avg QP:32.51 kb/s: 5411.77
x265 [info]: Weighted P-Frames: Y:7.0% UV:6.8%
x265 [info]: Weighted B-Frames: Y:18.4% UV:17.2%
x265 [info]: consecutive B-frames: 5.6% 3.6% 11.8% 22.0% 17.3% 11.6% 7.3% 5.3% 2.9% 1.9% 1.5% 2.2% 0.8% 0.9% 0.7% 1.5% 2.9%
encoded 10162 frames in 105460.05s (0.10 fps), 5624.43 kb/s, Avg QP:32.40
[aac @ 0x564f770d19e0] Qavg: 156.304
感谢您的阅读！
答案1
建议您坚持常规预设。
尚未检查所有自定义参数，但确实注意到您有cu-lossless=1。这告诉 x265 在 CU 级别评估无损编码作为选项。如此编码的 CU 将不会应用任何变换/量化，并且熵编码对结果残差的影响也将更大。
此外，x265 文档说，
--psy-rd 影响 RDO 决策，使其有利于节省能量（细节）而不是降低比特成本，从而对更多块进行无损编码。
并且您已经设置psy-rd=2.0