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tonemap filterchain 1

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This commit is contained in:
Manav Rathi
2025-04-24 13:30:29 +05:30
parent 004525ddeb
commit c040ae9dcc
1 changed files with 38 additions and 12 deletions
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50
desktop/src/main/services/ffmpeg.ts
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@@ -182,12 +182,10 @@ export const ffmpegGenerateHLSPlaylistAndSegments = async (
// purpose here we can treat it as as alias.
//
// BT.709 is the most common amongst these for older files out stored on
// computers, and they conform mostly to the standard with two caveats:
//
// 1. The files might not be properly "tagged" with the metadata of which
// colorspace etc they are using, and
// 2. The standard recommends using the yuv422p format, but de facto yuv420p
// is used (primarily because many video players only support yuv420p).
// computers, and they conform mostly to the standard (one notable exception
// is that the BT.709 standard also recommends using the yuv422p pixel
// format, but de facto yuv420p is used because many video players only
// support yuv420p).
//
// Since BT.709 is the most widely supported standard, we use it when
// generating the HLS playlist so to allow playback across the widest
@@ -198,8 +196,8 @@ export const ffmpegGenerateHLSPlaylistAndSegments = async (
// that uses the tonemap filter.
//
// However applying this tonemap to videos that are already HD leads to a
// brightness drop. So we conditionally apply it if the colorspace is not
// already BT.709.
// brightness drop. So we conditionally apply this filter chain only if the
// colorspace is not already BT.709.
//
// Reference:
// - https://trac.ffmpeg.org/wiki/colorspace
@@ -276,11 +274,39 @@ export const ffmpegGenerateHLSPlaylistAndSegments = async (
// Convert the video to a constant 30 fps, duplicating or
// dropping frames as necessary.
"fps=30",
// Output to YUV planar color space with "limited" but most
// compatible 4:2:0 chroma subsampling (if not specified, ffmpeg
// may output to a pixel format that is not widely supported).
// If the video is not in the HD color space (bt709), convert
// it. Before conversion, tone map colors so that they work the
// same across the change in the dyamic range.
//
// 1. The tonemap filter only works linear light, so we first
// use zscale with transfer=linear to linearize the input.
//
// 2. Then we use the tonemap, with the hable option that is
// best for preserving details.
//
// 3. Use zscale again to "convert to BT.709" by asking it to
// set the all three of color primaries, transfer
// characteristics and colorspace matrix to 709 (Note: the
// constants specified in the tonemap filter help do not
// include the "bt" prefix)
//
// See: https://ffmpeg.org/ffmpeg-filters.html#tonemap-1
//
// See: [Note: Tonemapping HDR to HD]
//
isBT709
? []
: [
"zscale=transfer=linear",
"tonemap=tonemap=hable",
"zscale=primaries=709:transfer=709:matrix=709",
],
// Use the most widely supported pixel format: 8-bit YUV planar
// color space with 4:2:0 chroma subsampling.
"format=yuv420p",
].join(","),
]
.flat()
.join(","),
],
// Video codec H.264
//