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Improve Transcode Quality #371

Merged
merged 12 commits into from
Aug 30, 2023
Merged

Improve Transcode Quality #371

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e3dc8d1
Test transcoding quality
leszko Aug 14, 2023
b3b66ca
Fix for testing in GCP
leszko Aug 16, 2023
5b6c119
Add CRF param
leszko Aug 16, 2023
3a68bd2
Add preset and tier params
leszko Aug 28, 2023
720e18a
Add CRF param
leszko Aug 29, 2023
4f482c9
Update CQ param
leszko Aug 29, 2023
8396865
Updates for testing
leszko Aug 29, 2023
3948710
Updates before PR
leszko Aug 29, 2023
e9afe5d
Add CRF to JsonProfile
leszko Aug 29, 2023
56d3191
Update how cq is calculated from crf
leszko Aug 30, 2023
5432f68
Introduce range for CRF and CQ params
leszko Aug 30, 2023
f718efe
Update how cq is calculated from crf
leszko Aug 30, 2023
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18 changes: 18 additions & 0 deletions ffmpeg/ffmpeg.go
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Original file line number Diff line number Diff line change
Expand Up @@ -694,6 +694,24 @@ func createCOutputParams(input *TranscodeOptionsIn, ps []TranscodeOptions) ([]C.
if len(p.VideoEncoder.Name) <= 0 && len(p.VideoEncoder.Opts) <= 0 {
p.VideoEncoder.Opts = map[string]string{
"forced-idr": "1",
"preset": "slow",
"tier": "high",
}
if p.Profile.CRF != 0 {
if p.Profile.CRF <= 63 {
p.VideoEncoder.Opts["crf"] = strconv.Itoa(int(p.Profile.CRF))
} else {
glog.Warning("Cannot use CRF param, value out of range (0-63)")
}

// There's no direct numerical correspondence between CQ and CRF.
// From some experiments, it seems that setting CQ = CRF + 7 gives similar visual effects.
cq := p.Profile.CRF + 7
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@emranemran emranemran Aug 31, 2023 •
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How did you end up with this formula? Lower CQ values typically indicate better quality at expense of compressions. Also encoders typically will pick either CQ and CRF as the main control so I'm not sure if CQ here will actually make a difference. Do you see a difference if we leave out CQ changes here?

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CRF is used by CPU-based transcoding, CQ is used by GPU-based transcoding.
So, only one of these values will be used at the time.

Technically there is no direct numerical correspondence between CQ and CRF, so the other option would be to set both CRF and CQ in our API. But I think it's not a pragmatic approach right now. Most of our transcoders are GPU anyway.

How did I come with cq := p.Profile.CRF + 7, just experimenting with videos. But obviously not for all videos it will give the same results, since technically CRF and CQ values do not correspond to each other.

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The cq := p.Profile.CRF + 7 doesn't quite make sense to me esp since they don't correspond to one another. Also if CRF is CPU only, then why do we need it?

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Explained here: https://discord.com/channels/423160867534929930/1140578841136484402/1149041283583721634

lets discuss more in discord

if cq <= 51 {
p.VideoEncoder.Opts["cq"] = strconv.Itoa(int(cq))
} else {
glog.Warning("Cannot use CQ param, value out of range (0-51)")
}
}
switch p.Profile.Profile {
case ProfileH264Baseline, ProfileH264ConstrainedHigh:
Expand Down
29 changes: 18 additions & 11 deletions ffmpeg/videoprofile.go
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Expand Up @@ -75,17 +75,18 @@ var FfmpegNameToVideoCodec = map[string]VideoCodec{
"vp9": VP9,
}

//Standard Profiles:
//1080p60fps: 9000kbps
//1080p30fps: 6000kbps
//720p60fps: 6000kbps
//720p30fps: 4000kbps
//480p30fps: 2000kbps
//360p30fps: 1000kbps
//240p30fps: 700kbps
//144p30fps: 400kbps
// Standard Profiles:
// 1080p60fps: 9000kbps
// 1080p30fps: 6000kbps
// 720p60fps: 6000kbps
// 720p30fps: 4000kbps
// 480p30fps: 2000kbps
// 360p30fps: 1000kbps
// 240p30fps: 700kbps
// 144p30fps: 400kbps
type VideoProfile struct {
Name string
Name string
// Bitrate is used to set min, avg, and max bitrate
Bitrate string
Framerate uint
FramerateDen uint
Expand All @@ -97,9 +98,13 @@ type VideoProfile struct {
Encoder VideoCodec
ColorDepth ColorDepthBits
ChromaFormat ChromaSubsampling
// CRF is used to set CRF and CQ
// If set, then constant rate factor is used instead of constant bitrate
// If both CRF and Bitrate are set, then Bitrate is used only as max bitrate
CRF uint
}

//Some sample video profiles
// Some sample video profiles
var (
P720p60fps16x9 = VideoProfile{Name: "P720p60fps16x9", Bitrate: "6000k", Framerate: 60, AspectRatio: "16:9", Resolution: "1280x720"}
P720p30fps16x9 = VideoProfile{Name: "P720p30fps16x9", Bitrate: "4000k", Framerate: 30, AspectRatio: "16:9", Resolution: "1280x720"}
Expand Down Expand Up @@ -230,6 +235,7 @@ type JsonProfile struct {
Encoder string `json:"encoder"`
ColorDepth ColorDepthBits `json:"colorDepth"`
ChromaFormat ChromaSubsampling `json:"chromaFormat"`
CRF uint `json:"crf"`
}

func ParseProfilesFromJsonProfileArray(profiles []JsonProfile) ([]VideoProfile, error) {
Expand Down Expand Up @@ -275,6 +281,7 @@ func ParseProfilesFromJsonProfileArray(profiles []JsonProfile) ([]VideoProfile,
ColorDepth: profile.ColorDepth,
// profile.ChromaFormat of 0 is default ChromaSubsampling420
ChromaFormat: profile.ChromaFormat,
CRF: profile.CRF,
}
parsedProfiles = append(parsedProfiles, prof)
}
Expand Down
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