Smart HEVC/H.264/MPEG-2 Transcoding

ffmpeg-smart.sh

#!/bin/bash
set -euo pipefail

LOG_PREFIX="[ffmpeg-smart]"

# Parse args
AGENT=""
URL=""
while [[ $# -gt 0 ]]; do
    if [[ "$1" == "-user_agent" ]]; then
        AGENT="$2"
        shift 2
    elif [[ "$1" == "-i" ]]; then
        URL="$2"
        shift 2
    else
        shift
    fi
done

# Validate URL
if [[ -z "$URL" ]]; then
    echo "$LOG_PREFIX ERROR: No stream URL provided" >&2
    exit 1
fi

# Probe stream
PROBE=$(ffprobe -user_agent "$AGENT" -v quiet -print_format json -show_streams "$URL" 2>&1) || {
    echo "$LOG_PREFIX ERROR: ffprobe failed - cannot access stream" >&2
    exit 1
}

# Parse streams by codec_type
VCODEC=$(echo "$PROBE" | jq -r '.streams[] | select(.codec_type=="video") | .codec_name' | head -n1)
FPS_FRAC=$(echo "$PROBE" | jq -r '.streams[] | select(.codec_type=="video") | .r_frame_rate' | head -n1)
ABITRATE_RAW=$(echo "$PROBE" | jq -r '.streams[] | select(.codec_type=="audio") | .bit_rate // empty' | head -n1)
ACHANNELS=$(echo "$PROBE" | jq -r '.streams[] | select(.codec_type=="audio") | .channels // empty' | head -n1)

# Validate video stream
if [[ -z "$VCODEC" || "$VCODEC" == "null" ]]; then
    echo "$LOG_PREFIX ERROR: No video stream found" >&2
    exit 1
fi

# Set video codec
if [[ "$VCODEC" == "hevc" ]]; then
    VCODEC_OUT="hevc_qsv"
    TAG_ARGS="-tag:v hvc1"
elif [[ "$VCODEC" == "h264" ]]; then
    VCODEC_OUT="h264_qsv"
    TAG_ARGS=""
elif [[ "$VCODEC" == "mpeg2video" ]]; then
    VCODEC_OUT="mpeg2_qsv"
    TAG_ARGS=""
else
    VCODEC_OUT="h264_qsv"
    TAG_ARGS=""
fi

# Validate audio bitrate (reject sample rates like 44100/48000)
if [[ -n "$ABITRATE_RAW" ]] && [[ "$ABITRATE_RAW" -ge 60000 ]] && [[ "$ABITRATE_RAW" -le 500000 ]]; then
    ABITRATE="$ABITRATE_RAW"
else
    ABITRATE="128000"
fi

# Set channel layout based on channel count
CHANNEL_LAYOUT=""
case "$ACHANNELS" in
    1)
        CHANNEL_LAYOUT="-channel_layout mono"
        ;;
    2)
        CHANNEL_LAYOUT="-channel_layout stereo"
        ;;
    6)
        CHANNEL_LAYOUT="-channel_layout 5.1"
        ;;
    8)
        CHANNEL_LAYOUT="-channel_layout 7.1"
        ;;
    *)
        # No audio detected OR unknown channel count - force stereo for compatibility
        CHANNEL_LAYOUT="-ac 2 -channel_layout stereo"
        ACHANNELS="${ACHANNELS:-0} -> 2 (forced)"
        ;;
esac

# Bitrates
VBITRATE="8000000"
MAXRATE="10000000"
BUFSIZE="20000000"

# Calculate GOP with rounding
if [[ "$FPS_FRAC" =~ ^([0-9]+)/([0-9]+)$ ]]; then
    NUM=${BASH_REMATCH[1]}
    DEN=${BASH_REMATCH[2]}
    if [[ $DEN -gt 0 ]]; then
        GOP=$(( (NUM + DEN/2) / DEN ))
        FPS_OUT="$FPS_FRAC"
        GOP_WARN=""
    else
        GOP=50
        FPS_OUT="25/1"
        GOP_WARN=" (invalid fps denominator)"
    fi
else
    GOP=50
    FPS_OUT="25/1"
    GOP_WARN=" (fps parse failed)"
fi

# Single combined log line
echo "$LOG_PREFIX Detected $VCODEC @ $FPS_FRAC -> $VCODEC_OUT GOP=$GOP${GOP_WARN} audio=${ABITRATE}bps ${ACHANNELS}ch" >&2

# Execute ffmpeg
exec ffmpeg \
  -user_agent "$AGENT" \
  -hwaccel qsv \
  -hwaccel_output_format qsv \
  -reconnect 1 \
  -reconnect_at_eof 1 \
  -reconnect_streamed 1 \
  -reconnect_delay_max 30 \
  -rw_timeout 15000000 \
  -fflags +genpts+igndts+discardcorrupt \
  -err_detect ignore_err \
  -i "$URL" \
  -map 0:v:0 \
  -map 0:a:0? \
  -c:v "$VCODEC_OUT" \
  -preset fast \
  -b:v "$VBITRATE" \
  -maxrate "$MAXRATE" \
  -bufsize "$BUFSIZE" \
  -g "$GOP" \
  -bf 0 \
  -look_ahead 0 \
  -fps_mode cfr \
  -r "$FPS_OUT" \
  -async 1 \
  $TAG_ARGS \
  -c:a aac \
  -b:a "$ABITRATE" \
  $CHANNEL_LAYOUT \
  -af "aresample=async=1" \
  -avoid_negative_ts make_zero \
  -start_at_zero \
  -mpegts_copyts 0 \
  -mpegts_flags +pat_pmt_at_frames+resend_headers \
  -flush_packets 1 \
  -max_muxing_queue_size 4096 \
  -f mpegts \
  pipe:1

Revision 3

Audio bitrate validation:

Added 60k-500k range check to reject corrupt metadata
Fixes streams with sample_rate (44100/48000) incorrectly set as bit_rate
Falls back to 128k for invalid/missing values

Revision 4

ffprobe now uses -user_agent "$AGENT".
Added TAG_ARGS="-tag:v hvc1" for HEVC output (empty for others).
GOP calc now guards against DEN=0 and also derives FPS_OUT (defaults to 25/1 when parsing fails).

ffmpeg changes:
-fflags adds +igndts
audio map is optional now: -map 0:a:0?
forces CFR: -fps_mode cfr -r "$FPS_OUT"
adds audio resample async filter: -af "aresample=async=1"
adds timestamp/TS stabilization: -avoid_negative_ts make_zero -start_at_zero -mpegts_copyts 0
formatted as multi-line for readability

Revision 5

Audio channel normalization:

• Detects source channel count (mono/stereo/5.1/7.1)
• Sets explicit -channel_layout for proper encoding
• Forces stereo for unknown/missing channel configs
• Logs channel count: audio=128000bps 6ch