Uses FFMPEG to convert any file FFMPEG understands into a .mp4 file that Telegram will consider as a 'gif', at higher quality than Telegram converts gifs to itself.

telegram-gif.sh

#!/bin/bash

# Settings
outfolder="converted"
codec="libx264"
maxres="448"
#filter="crop=floor(in_w/2)*2:floor(in_h/2)*2:0:0:exact=1,colorspace=bt601-6-625:range=pc:irange=tv:iall=bt601-6-625:format=yuv444p12,zscale=rin=full:tin=601:t=linear,scale=if(gt(iw\,ih)\,min($maxres\,floor((iw+1)/2)*2)\,-2):if(gt(iw\,ih)\,-2\,min($maxres\,floor((ih+1)/2)*2)),zscale=rin=full:r=limited:tin=linear:t=601"
filter="scale=if(gt(iw\,ih)\,min($maxres\,floor((iw+1)/2)*2)\,-2):if(gt(iw\,ih)\,-2\,min($maxres\,floor((ih+1)/2)*2)):out_color_matrix=bt601:out_range=tv:flags=accurate_rnd+full_chroma_inp+full_chroma_int+bicublin"
preset="veryslow"
profile="high"
tune="film"
quality="18"

# Input Parameters
inparams=(
	"-loglevel" "quiet"
	"-stats"
)

# Output Parameters
outparams=(
	"-flags" "+global_header"
	"-movflags" "faststart"
	"-c:v" "$codec"
	"-profile:v" "$profile"
	#"-tune:v" "$tune"
	"-bf" "0"
	"-copyts"
	"-avoid_negative_ts" "disabled"
	"-correct_ts_overflow" "0"
	"-pix_fmt" "yuv420p"
	"-color_primaries" "bt709"
	"-color_trc" "iec61966_2_1"
	"-colorspace" "bt470bg"
	"-color_range" "tv"
)

# Make a folder if it doesn't already exist.
function make_folder
{
	local folder="$1"

	if [ ! -d "$folder" ]; then
		mkdir "$folder"
	fi
}

# Move files to where they belong.
function detect_2pass
{
	local file="$1"
	local converted="$outfolder/$2"

	if [ ! -f "$converted" ]; then
		echo "$2 was not created!"
		return
	fi

	local size="$(stat -c%s "$converted")"

	if [ "$size" -gt 10485760 ]; then
		needs2pass+=("$file")
	fi
}

function framerate
{
	# If the file is a gif
	if [ "${file##*.}" == "gif" ]; then
		# Determine if the gif has a constant framerate
		local cfr="$(identify -format "%T\n" "$1" | awk 'BEGIN{getline;d=$0;if($0==0){d=10}c=1} {t=$0;if(t==0){t=10}if(t==d){next}else{c=0;exit}} END{printf("%d",c)}')"

		# If the framerate is variable
		if [[ "$cfr" -eq 0 ]]; then
			# Gets double the FPS based on the most commonly used frame duration.
			#fps=$(identify -format "%T\n" "$1" | awk 'max<++c[$0]{if($0==0){max=c[10];line=10}else{max=c[$0];line=$0}} END{printf("%.2f",200/line)}')

			# Gets double the minimum framerate.
			#fps=$(identify -format "%T\n" "$1" | awk 'BEGIN{getline;m=$0} {d=$0;if($0==0){d=10}if(d<m){m=d}} END{printf("200/%d",m)}')

			# Get size and duration of original gif
			local size="$(identify -format "%wx%h" "$1[0]")"
			local duration="$(identify -format "%T\n" "$1" | awk '{t+=$0;f++;if($0==0){t+=10}} END{printf("%.2f",t/100)}')"

			# Fix inaccurate gif duration
			# Commented out version had fixed some bug in the past related to off-by-one-frame duration issues.
			# I'm not seeing this anymore though, so I've made a simpler version that *seems* to work just fine.
			filter="color=s=$size:d=$duration:r=$fps:c=white[b];[0:v]fps=$fps:round=down[f];[b][f]overlay,$filter"
			#local filter="color=c=white:s=$size:d=$duration:r=$fps,select=between(t\,0\,$duration-(1/$fps))[b];[0:v]fps=$fps,select=between(t\,0\,$duration-(1/$fps))[f];[b][f]overlay,$filter"

		# Constant framerate
		else
			fps="$(identify -format "%T\n" "$1[0]" | awk '{d=$0;if(d==0){d=10}printf("100/%d",d)}')"
		fi

		if [[ "$fps" != *"/"* ]]; then
			fps="${fps}/1"
		fi

		local tb="${fps#*/}/${fps%/*}"

		outparams+=(
			"-r" "$fps"
			"-vsync" "cfr"
			"-time_base" "$tb"
			"-enc_time_base" "$tb"
			"-video_track_timescale" "$fps"
		)
	else
		duration="$(ffprobe -i "$1" -select_streams v:0 -show_entries stream=duration_ts -v quiet -of default=noprint_wrappers=1:nokey=1)"
		frames="$(ffprobe -i "$1" -select_streams v:0 -show_entries stream=nb_frames -v quiet -of default=noprint_wrappers=1:nokey=1)"
		tb="$(ffprobe -i "$1" -select_streams v:0 -show_entries stream=time_base -v quiet -of default=noprint_wrappers=1:nokey=1)"
		#ctb="$duration/$(($frames * ${tb#*/}))"
		#fps="$(($frames * ${tb#*/}))/$duration"

		local test="$(ffprobe -i "$1" -select_streams v:0 -show_entries stream=duration -v quiet -of default=noprint_wrappers=1:nokey=1)"

		if [ "$test" == "N/A" ]; then
			fps="$(ffprobe -i "$1" -select_streams v:0 -show_entries stream=r_frame_rate -v quiet -of default=noprint_wrappers=1:nokey=1)"
		else
			fps="$(ffprobe -i "$1" -select_streams v:0 -show_entries stream=time_base -v quiet -of default=noprint_wrappers=1:nokey=1 | sed -r 's/([0-9]+)\/([0-9]+)/\2\/\1/')"
		fi

		outparams+=(
			#"-time_base" "$tb"
			#"-enc_time_base" "-1"
			"-video_track_timescale" "$fps"
			"-vsync" "passthrough"
		)
	fi
}

# Convert all files with standard settings.
function conv
{
	local outparams=("${outparams[@]}")

	# Set fallback framerate of 25.
	local fps="25"
	local filter="$filter"
	local tags=""

	framerate "$1"

	# Qualaity and preset are different for 2-pass encoding, so can't keep them in the base array.
	# Filter gets changed by other parameters, so can't be either.
	outparams+=(
		"-qp" "$quality"
		"-preset" "$preset"
		"-lavfi" "$filter"
	)

	if [ -f "backup/$2" ]; then
		if [ "$(attr "backup/$2" -ql)" == "xdg.tags" ]; then
			tags="$(attr "backup/$2" -qg xdg.tags)"
		fi
	fi

	echo "$1 -> $2"
	ffmpeg "${inparams[@]}" -i "$1" "${outparams[@]}" -an "$outfolder/$2"

	if [ "$tags" != "" ]; then
		attr "$outfolder/$2" -qs xdg.tags -V "$tags"
	fi

	detect_2pass "$1" "$2"
}

# Attempt 2-pass conversion on files that are too large.
function run_2pass
{
	if [ "${1##*.}" == "gif" ]; then
		local duration="$(identify -format "%T\n" "$1" | awk '{t+=$0;f++;if($0==0){t+=10}} END{printf("%.2f",t/100)}')"
	else
		local duration="$(ffprobe -i "$1" -select_streams v:0 -show_entries format=duration -v quiet -of csv=p=0)"
	fi
	local bitrate="$((49807360/(625*${duration%.*})))k"
	local outparams=("${outparams[@]}")
	local fps="25"
	local tags=""

	framerate "$1"

	outparams+=(
		"-passlogfile" "pass/ffmpeg2pass"
		"-b:v" "$bitrate"
		"-preset" "placebo"
		"-lavfi" "$filter"
	)

	if [ -f "backup/$2" ]; then
		if [ "$(attr "backup/$2" -ql)" == "xdg.tags" ]; then
			tags="$(attr "backup/$2" -qg xdg.tags)"
		fi
	fi

	make_folder "pass"

	echo "$1 -> $2; pass 1"
	ffmpeg "${inparams[@]}" -i "$1" "${outparams[@]}" -pass 1 -an -y -f mp4 /dev/null

	echo "$1 -> $2; pass 2"
	ffmpeg "${inparams[@]}" -i "$1" "${outparams[@]}" -pass 2 -an -y "$outfolder/$2"

	if [ "$tags" != "" ]; then
		attr "$outfolder/$2" -qs xdg.tags -V "$tags"
	fi

	detect_2pass "$1" "$2"
}

needs2pass=()

make_folder "$outfolder"

shopt -s nullglob
for file in *.*; do
	shopt -u nullglob
	converted="${file%.*}.mp4"

	if [ -f "$outfolder/$converted" ]; then
		detect_2pass "$file" "$converted"
	else
		conv "$file" "$converted"
	fi
done

for file in "${needs2pass[@]}"; do
	converted="${file%.*}.mp4"
	needs2pass=("${needs2pass[@]:1}")

	run_2pass "$file" "$converted"
done

if [ ${#needs2pass[@]} -gt 0 ]; then
	make_folder "$outfolder/toobig"

	for failed in "${needs2pass[@]}"; do
		converted="${failed%.*}.mp4"

		mv "$outfolder/$converted" "$outfolder/toobig/$converted"
	done
fi