• man page
• All Options

• ffmpeg with Nvidia GPU

• https://www.ramugedia.com/how-encode-decode-hevc-h-265-by-intel-quick-sync-video-hw--qsv-
• https://trac.ffmpeg.org/wiki/Hardware/QuickSync
• https://gist.github.com/andrearug/ee461152acfbbd3f52b3bb9ffb55b6b8
• https://geoffruddock.com/bulk-compress-videos-x265-with-ffmpeg/
• https://slhck.info/video/2017/02/24/crf-guide.html
• https://netflixtechblog.com/a-large-scale-comparison-of-x264-x265-and-libvpx-a-sneak-peek-2e81e88f8b0f
• https://www.youtube.com/watch?v=wi1BefrfTos
• https://video.stackexchange.com/questions/14907/how-to-downsample-4k-to-1080p-using-ffmpeg-while-maintaining-the-quality

• https://github.com/markus-perl/ffmpeg-build-script

• https://trac.ffmpeg.org/wiki/AudioChannelManipulation#a5.1stereo
• https://superuser.com/a/1616102
• https://datatracker.ietf.org/doc/html/rfc7845#section-5.1.1.5

FL, FC, FR, BL, BR, LFE → FL, FR

-ac 2 \
-af "pan=stereo|FL = 0.374107*FC + 0.529067*FL + 0.458186*BL + 0.264534*BR + 0.374107*LFE |FR = 0.374107*FC + 0.529067*FR + 0.458186*BR + 0.264534*BL + 0.374107*LFE" \

FL, FC, FR, SL, SR, BL, BR, LFE → FL, FR

-ac 2 \
-af "pan=stereo|FL = 0.274804*FC + 0.388631*FL + 0.336565*SL + 0.194316*SR + 0.336565*BL + 0.194316*BR + 0.274804*LFE | FR = 0.274804*FC + 0.388631*FR + 0.336565*SR + 0.194316*SL + 0.336565*BR + 0.194316*BL + 0.274804*LFE" \

FL, FC, FR, SL, SR, BC, LFE → FL, FR

-ac 2 \
-af "pan=stereo|FL = 0.321953*FC + 0.455310*FL + 0.394310*SL + 0.227655*SR + 278819*BC + 0.321953*LFE | FR = 0.321953*FC + 0.455310*FR + 0.394310*SR + 0.227655*SL + 278819*BC + 0.321953*LFE" \

FL, FC, FR, BL, BR → FL, FR

-ac 2 \
-af "pan=stereo|FL = 0.460186*FC + 0.650802*FL + 0.563611*BL + 0.325401*BR | FR = 0.460186*FC + 0.650802*FR + 0.563611*BR + 0.325401*BL" \

FL, FR, BL, BR → FL, FR

-ac 2 \
-af "pan=stereo|FL = 0.422650*FL + 0.366025*BL + 0.211325*BR | FR = 0.422650*FR + 0.366025*BR + 0.211325*BL" \

FL, FC, FR → FL, FR

-ac 2 \
-af "pan=stereo|FL = 0.414214*FC + 0.585786*FL | FR = 0.414214*FC + 0.585786*FR" \

Quality with QSV as not good at all, though this could have been my fault.

ffmpeg \
  -y \
  -hwaccel qsv \
  -qsv_device /dev/dri/card0 \
  -c:v hevc_qsv \
  -i input.mkv \
  -c:v hevc_qsv \
  -vf 'scale_qsv=w=1920' \
  -preset slow \
  -global_quality 25 \
  -c:a copy \
  -c:s copy \
  output.mkv

• libx264
• libx265

ffmpeg \
  -i MyMovie_4K.mkv \
  -vf scale=1920:-1 \
  -c:v libx265 \
  -preset veryslow \
  -c:a copy \
  MyMovie_1080p.mkv

Not sure if these are necessary.

-crf 28

• https://gist.github.com/kurlov/32cbe841ea9d2b299e15297e54ae8971

ffmpeg \
  -i in.mkv \
  -f srt \
  -i in.srt \
  -map 0:0 \
  -map 0:1 \
  -map 1:0 \
  -c:v copy \
  -c:a copy \
  -c:s srt \
  out.mkv

http://diantokam.blogspot.com/2016/12/adding-subtitle-and-scaling-film-using.html

ffmpeg \
  -i "input.mkv" \
  -vf subtitles=fullsubs.srt \
  "output.mkv"

  # export english subs
  ffmpeg \
    -y \
    -i "./${name}" \
    -map 0:s:0 \
    eng.srt

  # create a version with hardsubs
  # si=0
  ffmpeg \
    -y \
    -i "./${name}" \
    -vf subtitles="${name}":si=0 \
    -ac 2 \
    -af "pan=stereo|FL = 0.374107*FC + 0.529067*FL + 0.458186*BL + 0.264534*BR + 0.374107*LFE |FR = 0.374107*FC + 0.529067*FR + 0.458186*BR + 0.264534*BL + 0.374107*LFE" \
    -c:a aac \
    "${name}-hardsubs.mp4"

ffmpeg \
  -itsoffset -1 \
  -i full8.srt \
  -c copy \
  full8_delayed.srt

https://hub.docker.com/r/tiangolo/nginx-rtmp https://www.nginx.com/blog/video-streaming-for-remote-learning-with-nginx/

ffmpeg -h encoder=hevc_qsv

ffmpeg \
  -i  input.mkv \
  -ss 29:36 \
  -to 29:50 \
  -c:v copy \
  -c:a aac \
  output.mp4

1. Install docker
2. Install nvidia docker: https://docs.nvidia.com/datacenter/cloud-native/container-toolkit/install-guide.html
3. Docker ffmpeg image: https://hub.docker.com/r/jrottenberg/ffmpeg

docker run \
  -v $(pwd):$(pwd) \
  -w $(pwd) \
  --runtime=nvidia jrottenberg/ffmpeg:4.1-nvidia \
  -hwaccel cuvid \
  -c:v h264_cuvid \
  -i input.mkv \
  -c:v hevc_nvenc \
  -c:a copy \
  -c:s copy \
  -preset slow \
  output_hevc.mkv

[h264 @ 0x56028de15ec0] Error creating a NVDEC decoder: 1
[h264 @ 0x56028de15ec0] Using more than 32 (34) decode surfaces might cause nvdec to fail.
[h264 @ 0x56028de15ec0] Try lowering the amount of threads. Using 16 right now.
[h264 @ 0x56028de15ec0] Failed setup for format cuda: hwaccel initialisation returned error.

• https://ffmpeg.org/pipermail/ffmpeg-user/2019-June/044610.html

Note that cuda hwaccel is an alias to the newer nvdec implementation, and to my knowledge, has no way of setting up decoder surface limits.

Here's a workaround you can try:

ffmpeg \
  -threads 4 \
  -hide_banner \
  -c:v h264_cuvid \
  -surfaces 8 \
  -nostats \
  -i rtmp://<ip>:<port>/myapp/mystream \
  -filter_complex [0]fps=fps=1[s0] \
  -map [s0] \
  -f rawvideo \
  -pix_fmt rgb24 pipe

Two changes:

1: Call up the h264_cuvid decoder directly, and apply a surface limit count of 8. This should be adequate.
2: Limit the thread count.

None of this worked.

• https://stackoverflow.com/a/48874015

[matroska @ 0x55a1a3738340] Non-monotonous DTS in output stream 0:1; previous: 490791, current: 490731; changing to 490791. This may result in incorrect timestamps in the output file.

Try -use_wallclock_as_timestamps 1 and -fflags +genpts

• https://stackoverflow.com/a/65501876

Add the following after the input file:

-max_muxing_queue_size 9999

[matroska @ 0x55e337388d80] Subtitle codec 96257 is not supported.
Could not write header for output file #0 (incorrect codec parameters ?): Function not implemented
Error initializing output stream 0:1 -- 
Conversion failed!

https://video.stackexchange.com/a/17009

stream apparently is a CEA-608 subtitle stream, which during the days of analog television signal transmission was caption data embedded within the video data. Apparently FFmpeg can extract it but can't mux it to a new container.

It doesn't seem like there's a whole lot that can be done.

• https://www.reddit.com/r/ffmpeg/comments/r2toyz/mp4_to_mkv_conversion_problem/

Convert the subtitles to SRT.

-c:s srt

[mpeg4 @ 0x5607fe47e0c0] Video uses a non-standard and wasteful way to store B-frames ('packed B-frames'). Consider using the mpeg4_unpack_bframes bitstream filter without encoding but stream copy to fix it.

• https://superuser.com/a/1099571

B-frames are a frame type used in video compression to represent frames of a video. B-frames can use information from both previous and future frames to represent each video frame.

Older DivX-encoded videos commonly use an ugly method called packed bitstream which puts several video frames into a single AVI chunk. Packed bitstream isn't standard MPEG-4, uses more space, requires more CPU power to encode/decode, and (most importantly) may cause problems if copied into another container type. This is the main reason for the warning.

Since you're re-encoding the video instead of just copying it, you should be fine. If you wanted to keep the original video, but copy it into another type of container (say MP4 or MKV), it'd be best to unpack the B-frames first using the FFmpeg filter mpeg4_unpack_bframes.

You could unpack the B-frames with something simple like

ffmpeg -i INPUT.avi -codec copy -bsf:v mpeg4_unpack_bframes OUTPUT.avi