ffmpeg WebM to MP4: ужасное качество видео

Я пытаюсь преобразовать видео WebM с веб-камеры в формат MP4 x264. Я пытался использовать эту команду ffmpeg:

ffmpeg -stats -nostdin -y -flags global_header -i "/home/Foto/incoming-video/2017-05-01-122614.webm" -c:v libx264 -preset slower -crf 20 -c:a aac "/home/Foto/rename-video/webm-test.mp4"

Журнал, поступающий от команды:

ffmpeg version 3.4.2-1~16.04.york0 Copyright (c) 2000-2018 the FFmpeg developers built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.6) 20160609 configuration: --prefix=/usr --extra-version='1~16.04.york0' --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth -enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgs --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex -enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enabl-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared libavutil 55. 78.100 / 55. 78.100 libavcodec 57.107.100 / 57.107.100 libavformat 57. 83.100 / 57. 83.100 libavdevice 57. 10.100 / 57. 10.100 libavfilter 6.107.100 / 6.107.100 libavresample 3. 7. 0 / 3. 7. 0 libswscale 4. 8.100 / 4. 8.100 libswresample 2. 9.100 / 2. 9.100 libpostproc 54. 7.100 / 54. 7.100 Input #0, matroska,webm, from '/home/Foto/incoming-video/2017-05-01-122614.webm': Metadata: encoder : GStreamer matroskamux version 1.8.3 creation_time : 2017-05-01T10:26:14.000000Z Duration: 00:00:57.57, start: 0.000000, bitrate: 3198 kb/s Stream #0:0(eng): Video: vp8, yuv420p(progressive), 1280x720, SAR 1:1 DAR 16:9, 250 tbr, 1k tbn, 1k tbc (default) Metadata: title : Video Stream #0:1(eng): Audio: vorbis, 44100 Hz, mono, fltp (default) Metadata: title : Audio Stream mapping: Stream #0:0 -> #0:0 (vp8 (native) -> h264 (libx264)) Stream #0:1 -> #0:1 (vorbis (native) -> aac (native)) [libx264 @ 0x55cb6afacd80] using SAR=1/1 [libx264 @ 0x55cb6afacd80] using cpu capabilities: MMX2 SSE2Fast SSSE3 Cache64 [libx264 @ 0x55cb6afacd80] profile High, level 5.1 [libx264 @ 0x55cb6afacd80] 264 - core 152 r2854 e9a5903 - H.264/MPEG-4 AVC codec - Copyleft 2003-2017 - http://www.videolan.org/x264.html - options: cabac=1 ref=8 deblock=1:0:0 analyse=0x3:0x133 me=umh subme=9 psy=1 psy_rd=1.00:000 mixed_ref=1 me_range=16 chroma_me=1 trellis=2 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=3 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframs=3 b_pyramid=2 b_adapt=2 b_bias=0 direct=3 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=60 rc=crf mbtree=1 crf=20.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00 Output #0, mp4, to '/home/Foto/rename-video/webm-test.mp4': Metadata: encoder : Lavf57.83.100 Stream #0:0(eng): Video: h264 (libx264) (avc1 / 0x31637661), yuv420p, 1280x720 [SAR 1:1 DAR 16:9], q=-1--1, 250 fps, 16k tbn, 250 tbc (default) Metadata: title : Video encoder : Lavc57.107.100 libx264 Side data: cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1 Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 69 kb/s (default) Metadata: title : Audio encoder : Lavc57.107.100 aac More than 1000 frames duplicated More than 10000 frames duplicated frame=14392 fps= 14 q=-1.0 Lsize= 44929kB time=00:00:57.55 bitrate=6394.8kbits/s dup=12683 drop=0 speed=0.0575x video:44230kB audio:489kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.471058% [libx264 @ 0x55cb6afacd80] frame I:61 Avg QP:17.26 size: 98800 [libx264 @ 0x55cb6afacd80] frame P:3627 Avg QP:20.45 size: 10478 [libx264 @ 0x55cb6afacd80] frame B:10704 Avg QP:23.79 size: 118 [libx264 @ 0x55cb6afacd80] consecutive B-frames: 0.8% 0.0% 0.0% 99.1% [libx264 @ 0x55cb6afacd80] mb I I16..4: 6.5% 79.7% 13.8% [libx264 @ 0x55cb6afacd80] mb P I16..4: 0.7% 1.6% 0.1% P16..4: 33.3% 4.7% 5.2% 0.0% 0.0% skip:54.3% [libx264 @ 0x55cb6afacd80] mb B I16..4: 0.0% 0.0% 0.0% B16..8: 3.2% 0.0% 0.0% direct: 0.0% skip:96.8% L0:30.0% L1:69.7% BI: 0.3% [libx264 @ 0x55cb6afacd80] 8x8 transform intra:71.1% inter:60.1% [libx264 @ 0x55cb6afacd80] direct mvs spatial:100.0% temporal:0.0% [libx264 @ 0x55cb6afacd80] coded y,uvDC,uvAC intra: 68.5% 91.9% 70.6% inter: 4.2% 7.6% 1.4% [libx264 @ 0x55cb6afacd80] i16 v,h,dc,p: 20% 17% 33% 30% [libx264 @ 0x55cb6afacd80] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 16% 11% 11% 6% 11% 15% 10% 10% 10% [libx264 @ 0x55cb6afacd80] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 15% 7% 5% 5% 24% 20% 9% 7% 7% [libx264 @ 0x55cb6afacd80] i8c dc,h,v,p: 50% 20% 16% 14% [libx264 @ 0x55cb6afacd80] Weighted P-Frames: Y:1.7% UV:0.9% [libx264 @ 0x55cb6afacd80] ref P L0: 68.7% 15.8% 8.2% 1.4% 1.9% 2.3% 1.3% 0.3% 0.0% [libx264 @ 0x55cb6afacd80] ref B L0: 92.5% 6.3% 0.7% 0.3% 0.1% 0.1% 0.0% [libx264 @ 0x55cb6afacd80] ref B L1: 95.0% 5.0% [libx264 @ 0x55cb6afacd80] kb/s:6293.87 [aac @ 0x55cb6afc6bc0] Qavg: 233.656 

Я заметил предупреждающее сообщение «Более 10000 кадров дублировано» во время сжатия видео. В конце я получил файл MP4 с ужасным качеством, отрывистое видео со множеством блоков, сильно отличающихся от оригинала (это было очень плавное видео с дискретным качеством кадра). Более того, размер выходного файла в два раза больше исходного (44 МБ вместо 22), поэтому я не понимаю причины этого недостатка качества.

Вы можете мне помочь?