For batch converting ISOs to a specific resolution and format while preserving folder hierarchy on Linux, you can indeed use ffmpeg with a bash script. However, you might also consider using HandBrakeCLI, which is a command-line interface for HandBrake, a popular video transcoder.

Here’s how you could use HandBrakeCLI to achieve your goal:

1. Install HandBrakeCLI if you haven’t already:

sudo apt-get install handbrake-cli

2. Write a bash script to iterate through your directories, converting ISO files:

#!/bin/bash

# Set input and output directories
input_dir="/path/to/your/input/directory"
output_dir="/path/to/your/output/directory"

# Convert ISOs to 720p h.265
find "$input_dir" -name "*.iso" -type f | while read -r file; do
    output_file="${file%.iso}.mp4"
    handbrakecli --input "$file" --output "$output_dir/$output_file" --preset="Super HQ 720p30 Surround"
done

Adjust the preset according to your needs. You can check available presets with HandBrakeCLI --preset-list.

3. Make the script executable:

chmod +x convert_iso.sh

4. Run the script:

./convert_iso.sh

This script will convert all ISO files in the specified input directory to 720p h.265 MP4 files using HandBrakeCLI while preserving the folder hierarchy.