VMAF with FFmpeg

Refer VMAF score to reduce bitrate of RTMP live streaming.

• VMAF
• Using VMAF with FFmpeg
• Model

Requirement

• FFmpeg built with --enable-libvmaf
• grep
• Only tested on macOS

Usage Example

I have published streaming with 700k with resolution 800x450.
Now, I want to reduce the bitrate, but don't want users feel bad quality than before.

Prepare Samples

1. Record stream video from OBS as stream_75s_raw_1920x1080.mp4. (Scripts will reference the naming pattern)
2. Convert stream_75s_raw_1920x1080.mp4 to prefer bitrate 700k as stream_75s_700k_800x450_h264.flv
3. Convert stream_75s_raw_1920x1080.mp4 to bitrates 576k, 448k, 384k for distored version.

see create_sample_h264.sh

Smaples

# Current streaming quality
./create_sample_h264.sh stream_75s_raw_1920x1080.mp4 700k 800x450
=> stream_75s_700k_800x450_h264.flv
# Sample 1
./create_sample_h264.sh stream_75s_raw_1920x1080.mp4 576k 800x450
=> stream_75s_576k_800x450_h264.flv
# Sample 2
./create_sample_h264.sh stream_75s_raw_1920x1080.mp4 448k 800x450
=> stream_75s_448k_800x450_h264.flv
# Sample 3
./create_sample_h264.sh stream_75s_raw_1920x1080.mp4 384k 800x450
=> stream_75s_384k_800x450_h264.flv

Sample for H265

• create_sample_h265.sh
  • Create H265 flv.
• create_sample_hevc_nvenc.ps1.sh
  • Create flv of hevc_nvenc codec with Nvidia grahpic card on Windows Poershell.
  • Install CUDA toolkit first.
  • FFmpeg for Windows

Caculation

see run_vmaf.sh

VMAF score

Prepare input1, input2 as reference and distored version to compare frame by frame.

Default model model/vmaf_v0.6.1.json is trained by 1920x1080 HDTV, the script will scale input1 and input2 to 1920x1080.

./run_vmaf.sh stream_75s_700k_800x450_h264.flv stream_75s_576k_800x450_h264.flv 1920x1080
./run_vmaf.sh stream_75s_700k_800x450_h264.flv stream_75s_448k_800x450_h264.flv 1920x1080
./run_vmaf.sh stream_75s_700k_800x450_h264.flv stream_75s_384k_800x450_h264.flv 1920x1080

Phone Model

# without phone model, can ignore last parameter 0
./run_vmaf.sh stream_75s_700k_800x450_h264.flv stream_75s_384k_800x450_h264.flv 1920x1080 0
# with phone model, the score is close to 99. (phone model trained by lower resolution)
./run_vmaf.sh stream_75s_700k_800x450_h264.flv stream_75s_384k_800x450_h264.flv 1920x1080 1

Comparison

• Raw video stream_75s_raw_1920x1080.mp4

reference	distored	scale	vmaf score
stream_75s_700k_800x450_h265.flv	stream_75s_576k_800x450_h264.flv	1920x1080	91.979802
...	stream_75s_448k_800x450.flv	1920x1080	90.303380
...	stream_75s_384k_800x450.flv	1920x1080	88.956422

• Define target score : Pick optimized bitrate to VMAF score between 90 ± 1.
• Pick 448k as new bitrate to reduce bandwidth of network.