Why Does Converting WEBM to Cropped MP4 Result in Bigger File Sizes?

Converting WebM Cropped MP4 Result: Bigger File Sizes?

Handbrake is a popular open-source transcoding tool used for converting video formats. When dealing with unseekable screen recordings in WebM format, you may encounter an issue where the output MP4 file is significantly larger than the input file, despite a decrease in resolution. This article will explore the potential reasons and solutions for this problem.

1. Handbrake settings and optimization

Handbrake offers various presets and settings that can impact the output file size. To minimize the file size, consider the following settings:

• Format: Choose MP4.
• Video Codec: H.264 (x264) or H.265 (x265) for better compression.
• Framerate (FPS): Match the source framerate.
• Quality: Use RF (Rate Factor) value between 18-24 for a good balance between quality and file size.
• Two-pass encoding: Enabled for better compression.

2. WebM vs MP4 container differences

WebM and MP4 are different container formats. WebM primarily uses the VP9 video codec, while MP4 can use H.264 or H.265. VP9 generally provides better compression than H.264, which might explain the smaller file size in WebM format.

3. Lossless vs lossy compression

WebM, by default, uses lossless compression, which retains all the original data. When converting to MP4, you need to use lossy compression, which discards some data to reduce file size. This difference in compression methods might result in a larger MP4 file.

4. Cropping and resolution changes

Cropping a video in Handbrake might result in a larger file size because the process increases the bitrate to maintain the same quality in the smaller area. Similarly, changing the resolution might also impact the file size.

5. Audio codec and format

WebM usually contains Opus or Vorbis audio codecs, while MP4 uses AAC. Changing the audio codec and format might contribute to the increased file size.

6. Workarounds and solutions

To minimize the file size when converting WebM to MP4, consider the following:

• Use a lower RF (Rate Factor) value in Handbrake.
• Convert the audio to a lower bitrate or mono format.
• Try different video codecs (H.264, H.265) and settings.
• Use an alternative transcoding tool like FFmpeg with specific settings and codecs.

Example FFmpeg command:

References

• Handbrake Documentation: https://handbrake.fr/docs.php
• x264 Encoding Guide: https://wiki.videolan.org/x264_Encoding_Guide
• FFmpeg Documentation: https://ffmpeg.org/documentation.html