How to stop ffmpeg from interlacing when converting from m2ts to mkv

Question

I have a m2ts video file that contains a h264 video stream and an ac3 audio stream. The quality is not the best, but it is okay, but converting it with ffmpeg without any additional options makes the video interlaced and very ugly with that:

ffmpeg -i input.m2ts output.mkv

Output:

ffmpeg version 3.2.2 Copyright (c) 2000-2016 the FFmpeg developers
  built with gcc 6.2.1 (GCC) 20160916 (Red Hat 6.2.1-2)
  configuration: --arch=x86_64 --bindir=/usr/bin --datadir=/usr/share/ffmpeg --disable-debug --disable-static --disable-stripping --enable-avfilter --enable-avresample --enable-bzlib --enable-cuda --enable-cuvid --enable-libnpp --enable-doc --enable-fontconfig --enable-frei0r --enable-gnutls --enable-gpl --enable-iconv --enable-libass --enable-libbluray --enable-libcdio --enable-libdc1394 --enable-libebur128 --enable-libfdk-aac --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libkvazaar --enable-libmfx --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenh264 --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libv4l2 --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxcb-shm --enable-libxcb-xfixes --enable-libxcb-shape --enable-libxvid --enable-libzvbi --enable-lzma --enable-nonfree --enable-openal --enable-opencl --enable-nvenc --enable-opengl --enable-postproc --enable-pthreads --enable-sdl2 --enable-shared --enable-version3 --enable-x11grab --enable-xlib --enable-zlib --extra-cflags='-I/usr/include/nvenc -I/usr/include/cuda' --incdir=/usr/include/ffmpeg --libdir=/usr/lib64 --mandir=/usr/share/man --optflags='-O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -m64 -mtune=generic' --prefix=/usr --shlibdir=/usr/lib64 --enable-runtime-cpudetect
  libavutil      55. 34.100 / 55. 34.100
  libavcodec     57. 64.101 / 57. 64.101
  libavformat    57. 56.100 / 57. 56.100
  libavdevice    57.  1.100 / 57.  1.100
  libavfilter     6. 65.100 /  6. 65.100
  libavresample   3.  1.  0 /  3.  1.  0
  libswscale      4.  2.100 /  4.  2.100
  libswresample   2.  3.100 /  2.  3.100
  libpostproc    54.  1.100 / 54.  1.100
Input #0, mpegts, from 'input.m2ts':
  Duration: 01:15:49.44, start: 0.984822, bitrate: 19636 kb/s
  Program 1 
    Stream #0:0[0x1011]: Video: h264 (High) (HDMV / 0x564D4448), yuv420p(tv, bt709, top first), 1920x1080 [SAR 1:1 DAR 16:9], 25 fps, 50 tbr, 90k tbn, 50 tbc
Stream #0:1[0x1100]: Audio: ac3 (AC-3 / 0x332D4341), 48000 Hz, stereo, fltp, 384 kb/s
File 'output.mkv' already exists. Overwrite ? [y/N] y
[libx264 @ 0xf21240] using SAR=1/1
[libx264 @ 0xf21240] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 AVX2 LZCNT BMI2
[libx264 @ 0xf21240] profile High, level 4.0
[libx264 @ 0xf21240] 264 - core 148 - H.264/MPEG-4 AVC codec - Copyleft 2003-2016 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=18 lookahead_threads=3 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, matroska, to 'output.mkv':
  Metadata:
    encoder         : Lavf57.56.100
    Stream #0:0: Video: h264 (libx264) (H264 / 0x34363248), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], q=-1--1, 25 fps, 1k tbn, 25 tbc
    Metadata:
      encoder         : Lavc57.64.101 libx264
    Side data:
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
    Stream #0:1: Audio: vorbis (libvorbis) (oV[0][0] / 0x566F), 48000 Hz, stereo, fltp
    Metadata:
      encoder         : Lavc57.64.101 libvorbis
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
  Stream #0:1 -> #0:1 (ac3 (native) -> vorbis (libvorbis))
Press [q] to stop, [?] for help

Additional options, like presets and crf did not change that and I could not find anything on the Internet except that ffmpeg is supposed to always use progressive unless told otherwise. I also tried hardware transcoding on my GPU, which made the transcode much much faster, but the result was about the same, still heavily interlaced video.

ffmpeg -hwaccel cuvid -c:v h264_cuvid -i input.m2ts -c:v hevc_nvenc -preset slow output.mkv

Any idea what might be causing this and how to fix it? Adding -deinterlace helps with the interlacing, but makes the quality worse.

Answer 1

The source is interlaced. To deinterlace it, you can use the yadif filter.

To use it with the default values:

ffmpeg -i input.m2ts -vf yadif=parity=auto output.mkv

Answer 2

You can try deinterlace it on decoding step with the following command:

ffmpeg -hwaccel cuvid -c:v h264_cuvid -deint 2 -drop_second_field 1 -i input.m2ts -c:v hevc_nvenc -preset slow output.mkv

Or keep interlacing with the next command:

ffmpeg -i input.m2ts -flags +ildct -c:v hevc_nvenc -preset slow output.mkv