AV1 vs. HEVC: Efficiently Archiving Ghibli Classics

I recently set out to optimize my Studio Ghibli collection by re-encoding Blu-ray discs into the AV1 format. My goal was to significantly reduce file sizes without compromising visual quality. AV1 was the ideal candidate due to its high compression efficiency, royalty-free licensing, and growing hardware support.

For this experiment, I chose the 1991 film "Only Yesterday". It is notoriously difficult to transcode due to persistent picture jitter and film grain (noise). Using FFmpeg 6.0, I compared HEVC and AV1, finding that a 10-bit depth and Constant Rate Factor (CRF) yielded the best results for both.

The Results

The AV1 encode was remarkably four times smaller (645 MB) than the HEVC version (2563 MB), despite maintaining nearly identical quality metrics. However, the trade-off was encoding time: using libaom, it took approximately three days to process the two-hour movie.

Encoding Parameters

HEVC (x265):

-c:v libx265 -preset slow -tune animation -profile:v main10 -pix_fmt yuv420p10le -crf 22 -x265-params crf=22:no-sao=1:no-fast-intra=1

AV1 (libaom):

-c:v libaom-av1 -pix_fmt yuv420p10le -b:v 0 -crf 30 -threads 8 -cpu-used 4 -aq-mode 1 -tune ssim -lag-in-frames 35 -arnr-max-frames 15 -arnr-strength 4 -aom-params tune=ssim:cq-level=30:cpu-used=4:noise-sensitivity=2:tune-content=default:arnr-strength=4:arnr-maxframes=15:enable-qm=1:enable-chroma-deltaq=1:quant-b-adapt=1

Quality Metrics Comparison

The metrics confirm that AV1 achieved the same visual fidelity as HEVC while using only 25% of the disk space. For archival purposes where storage is at a premium and encoding time is not a concern, AV1 is the clear winner.