125 lines
5.1 KiB
Bash
125 lines
5.1 KiB
Bash
#!/usr/bin/env bash
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# Re-encodes the video using a target quality level and a variable bitrate.
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# To have a mostly fixed bitrate with no variable quality, use trim-video-target-rate
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# Just note that it'll result in larger files for a similar max bitrate target and the
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# quality won't really be noticeably better.
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if which tput >/dev/null 2>&1; then
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ncolors=$(tput colors)
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fi
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if [ -t 1 ] && [ -n "$ncolors" ] && [ "$ncolors" -ge 8 ]; then
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RED="$(tput setaf 1)"
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GREEN="$(tput setaf 2)"
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YELLOW="$(tput setaf 3)"
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BLUE="$(tput setaf 4)"
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MAGENTA="$(tput setaf 5)"
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CYAN="$(tput setaf 6)"
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BOLD="$(tput bold)"
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NORMAL="$(tput sgr0)"
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else
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RED=""
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GREEN=""
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YELLOW=""
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BLUE=""
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MAGENTA=""
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CYAN=""
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BOLD=""
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NORMAL=""
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fi
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filename=$(basename -- "$1")
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output_name="$2"
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start_time="$3"
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end_time="$4"
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target_crf="$5"
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max_bitrate_mb="$6"
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default_crf="20"
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default_max_bitrate="6"
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if [[ $filename == "" || $output_name == "" || $start_time == "" ]]; then
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printf "${BOLD}${RED}Usage: trim-video <filename> <output name> <start time HH:MM:SS> <optional: end time HH:MM:SS, use empty string or 0 for no value> <optional: crf (quality, w/ lower = more compression) - defaults to $default_crf, use 0 for no value> <optional: max bitrate in MB - defaults to ${default_max_bitrate}M>${NORMAL}\n"
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exit 1
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fi
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extension="${filename##*.}"
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filename="${filename%.*}"
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output="${output_name}.$extension"
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if [[ $target_crf == "" || $target_crf == "0" ]] then
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target_crf=$default_crf
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fi
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if [[ $max_bitrate_mb == "" ]] then
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max_bitrate_mb=$default_max_bitrate
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fi
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# bufsize is typically double the maxrate
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bufsize=$((max_bitrate_mb * 2))
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bufsize="${bufsize}M"
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max_bitrate="${max_bitrate_mb}M"
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timing_args=""
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if [[ $start_time != "" ]]; then
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timing_args="-ss $start_time "
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fi
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if [[ $end_time != "" ]]; then
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if [[ $start_time == "0" && $end_time == "0" ]]; then
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# We treat a start and end with 0 values as no op.
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timing_args=""
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elif [[ $end_time != "0" ]]; then
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# Handle having a start time but end time is set to 0, can just ignore it and it'll use the remainder of the video.
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timing_args+="-to $end_time"
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fi
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fi
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printf "\n${YELLOW}${BOLD}Trimming '$filename.$extension' | output: $output | start: $start_time | end: $end_time | crf: $target_crf | max rate: $max_bitrate | buffer size: $bufsize ${NORMAL}\n"
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# You might have issues if the file has multiple video streams or embedded
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# subtitles. The -map 0 arg is typically given when copying a video stream, but
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# I'm not sure if it's appropriate to use here. If you want to target one of
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# the video streams then use `-map 0:v:0` and if you want to re-encode
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# subtitles then include `-c:s mov_text` with either of the `-map` args.
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# -preset 3 and 4 are the fastest on my 3080 and have the same output file
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# size. p3 seems slightly faster. Apparently 7 is the best for 30 series
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# according to chatgpt (lol) but it was slow and compressed.
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# -accurate_seek doesn't seem to be needed when -ss is after -i, only when -ss
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# is before -i. Having -ss after is apparently a way of enabling accurate seeking.
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# The catch is that if the trim doesn't start at 0, it can be a long wait before
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# the encoder gets to the portion you want to start trimming from. To speed this up
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# we are putting -ss and -accurate_seek before -i ... the video duration might be
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# slightly off from this but so far I haven't seen any seeking issues. If they come
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# up then we can move -ss to after -i again and delete -accurate_seek.
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# I'm using -rc:v vbr -cq:v 20 (higher = more compression) to have a variable
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# bit-rate with a quality target. This gives us a good looking re-encoding that
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# does a good job preserving the quality of the source video (at least for
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# twitch streams I'm trimming) but the bitrate might be higher or lower than
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# the source. The quality metric will fluctuate during encoding because NVENC
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# does't use a fixed quantization parameter. -cq:v is a target, not a constraint.
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# So you can have quite the fluctuating (or high) bitrate with these two params.
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# In order to set a birate cap that is prioritized over visual fidelity, we can
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# add in:
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# -maxrate:v -bufsize:v
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# (with bufsize typically being double the maxrate)
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#
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# Using this with the vbr and crf params tells the NVENC encoder to try to
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# encode at a perceptual quality level around CQ=20 but keep the bitrate under
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# 6000 kbps (constrained VBR). If a scene is too complex to maintain CQ=20
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# within the bitrate cap, the encoder will:
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# * Raise the quantizer (lower quality) to obey the -maxrate
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# * Result: CQ metric fluctuates upward
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# If a scene is simple:
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# * Encoder can exceed CQ=20 (e.g. better quality) while staying under maxrate
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# * Result: CQ metric fluctuates downward
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#
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# To have a mostly fixed bitrate with no variable quality, use trim-video-target-rate
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time ffmpeg -y -stats -loglevel level+error -hwaccel cuda -hwaccel_output_format cuda $timing_args -accurate_seek -i "$filename.$extension" -c:v h264_nvenc -profile:v high -preset 3 -rc:v vbr -cq:v $target_crf -maxrate:v $max_bitrate -bufsize:v $bufsize -c:a copy -movflags +faststart "$output"
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printf "\n${GREEN}${BOLD}Finished trimming${NORMAL}\n\n"
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