This batch script processes `.webm` files in the current directory...

This batch script processes .webm files in the current directory and converts them to .mp4 format using ffmpeg, provided that there exists a corresponding .webp file with the same base name. Here's a detailed explanation of what the code does step-by-step:

1. Loop Through .webm Files:

   • The loop for %%f in (*.webm) iterates over all .webm files in the current directory. For each file, the %%f variable holds the name of the current file, including its extension.

2. Check for Matching .webp File:

   • The script uses an if exist statement to check if a .webp file with the same base name as the current .webm file exists. The notation %%~nf extracts just the base name (name without extension) of the current file. If a corresponding .webp file is found, the code inside the if block is executed.

3. Run ffmpeg Command:

   • The ffmpeg command is executed to combine the .webm video input (%%f) with the .webp file (%%~nf.webp) as a second input. Here's what the components of the ffmpeg command do:
     • -y: Overwrites the output file without prompting.
     • -i "%%f": Specifies the .webm file as the first input.
     • -i "%%~nf.webp": Specifies the .webp file as the second input.
     • -map 0:v:0: Maps the first input’s primary video stream.
     • -map 0:a?: Maps the first input’s audio stream, if it exists (the ? makes this optional).
     • -map 1:v:0: Maps the .webp image as an additional video stream.
     • -filter:v:0 "scale=trunc(iw/2)*2:trunc(ih/2)*2": Ensures the video resolution is even (a requirement for many video codecs).
     • -c:v libx264: Encodes the primary video stream using the H.264 codec.
     • -crf 0: Sets lossless compression for the primary video stream.
     • -preset medium: Sets the H.264 encoder preset to "medium" for a balance of speed and compression efficiency.
     • -pix_fmt yuv420p: Ensures 8-bit YUV 4:2:0 pixel format for broad compatibility.
     • -c:a aac -b:a 192k: Encodes the audio stream using the AAC codec at a bitrate of 192 kbps.
     • -c:v:1 mjpeg: Sets the .webp image (second video stream) to be encoded as an MJPEG frame.
     • -disposition:v:1 attached_pic: Marks the second video stream as an attached picture (e.g., a thumbnail or cover art).
     • -movflags +faststart: Optimizes the output MP4 file for web streaming by moving metadata to the beginning of the file.
     • "%%~nf.mp4": Specifies the output file name, using the same base name as the input file but with an .mp4 extension.

4. Effect:

   • For each .webm file that has a corresponding .webp file, this script:
     • Converts the .webm file to an .mp4 file,
     • Ensures proper scaling and compression for the primary video,
     • Encodes any audio present in the .webm file,
     • Embeds the .webp file as an attached thumbnail in the .mp4 file.

In summary, this batch script converts .webm files to .mp4 with embedded thumbnails (from .webp files), along with adjustments to ensure compatibility and efficient playback.