How AV1 Cut Bandwidth Costs by 59% for a Popular Karaoke App

AV1 Adoption in 全民K歌

As a music‑entertainment social platform serving all ages, 全民K歌 saw video content grow year over year, putting significant pressure on bandwidth costs.

To address this, the team deployed cutting‑edge technology and fine‑grained operations, boosting AV1 video playback to about 60% of total plays and cutting bitrate by roughly 59%, which dramatically lowered costs and improved user experience.

Choosing AV1 and the TXAV1 Encoder

Among many codecs such as H.265 and AV1, the team selected AV1 for its compression potential and decoding compatibility. AV1 offers about a 20% compression gain over H.265 at comparable quality, and modern chips (e.g., Apple A17, flagship Android SoCs) now provide hardware decode support.

Tencent’s self‑developed TXAV1 encoder outperformed open‑source alternatives in the 2021/2022 MSU competition, winning 28 of 29 metrics. Compared with SVT‑AV1‑1.7, TXAV1 delivers 7‑11% additional compression, a 69% speedup, and up to 11.4× faster encoding at similar compression levels.

Key Technical Enhancements

The encoder improves compression through three main avenues: (1) more accurate prediction and motion estimation, (2) full‑dimensional adaptive quantization (frame‑level, GOP‑level, block‑level QP optimization), and (3) a high‑accuracy rate‑distortion model for optimal mode selection. Combined with the “极速高清” enhancement, AV1 videos achieve higher visual quality at lower bitrates.

Because many Android devices still lack AV1 hardware decode, the app added soft‑decode support and selected the Tencent txav1d decoder, which uses less CPU and memory than the open‑source dav1d and matches H.265 soft‑decode consumption.

Cost‑Saving Strategy and Playback Threshold

To avoid unnecessary transcoding costs, the team predicts video popularity and only transcodes works expected to exceed a calculated playback‑volume threshold. This threshold is derived from A/B experiments that measure per‑play bandwidth savings after AV1 transcoding.

AV1 bitrate selection follows a VMAF‑based adaptive bitrate (CAE) scheme, fixing visual quality loss while adapting bitrate to content, achieving 85% accuracy in the VMAF [-1, 1] range.

Device Compatibility Testing

iOS devices were fully tested before release. For Android, a tiered testing approach plus a blacklist based on frame‑drop rates (>0.5%) was used, resulting in over 80% of Android models supporting 720p @ 30 fps AV1 playback; unsupported devices fall back to other codecs.

Playback Optimizations for Music Highlights

Since users often seek directly to song highlights, the encoder places an I‑frame just before the highlight segment, eliminating the need to download extra frames and reducing start‑up latency.

Results and Future Outlook

AV1 now accounts for about 60% of video plays on the platform. Compared with H.264, bitrate is reduced by ~59% and overall bandwidth by 42%. First‑buffer time dropped 34.4%, second‑buffer time 49.4%, and average watch time increased by ~0.4%.

Looking ahead, the team expects that by the end of 2025 more than 50% of Android devices will support AV1 hardware decode, further enhancing performance and reducing power consumption.