ffmpeg Hardware Transcoding 10-bit HEVC to 8-bit H.264 with NVIDIA CUDA

nvidia_transcode.sh

#!/usr/bin/env bash

declare -a CMD_LINE

# We're running ffmpeg, of course
CMD_LINE+=(ffmpeg)
# Don't bother showing the ffmpeg banner, accept prompts by default
CMD_LINE+=(-hide_banner -y)
# Optionally limit CPU threads, really shouldn't be needed since everything is on the GPU
#CMD_LINE+=(-threads 8)
# Use CUDA hardware acceleration
CMD_LINE+=(-hwaccel cuda -hwaccel_output_format cuda)
# Offload video decoding to the GPU
CMD_LINE+=(-c:v hevc_cuvid)
# Input file from first argument
CMD_LINE+=(-i "$1")
# This matters! Don't autoscale or you get pixel format mis-matches!
CMD_LINE+=(-noautoscale)
# To perform on-GPU scaling, uncommont this line and specify your desired output resolution
# instead of 1920x1080!
#CMD_LINE+=(-filter_complex '[0:0]scale_cuda=1920:1080:format=yuv420p,hwdownload[out]' -map '[out]')
# Copy auto as-is
CMD_LINE+=(-map '0:a:0' -c:a copy)
# Re-encode as H.264 in regular 8-bit pixel format
CMD_LINE+=(-c:v h264_nvenc -pix_fmt yuv420p)
# Optionally specify a bitrate and encoding profile here
#CMD_LINE+=(-b:v 20M -profile main)
# Fast start, lets uploading/encoding be faster for sites like YouTube
CMD_LINE=+(-movflags +faststart)
# Output format from second argument
CMD_LINE+=("$2")

exec "${CMD_LINE[*]}"