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Handle even px requirement

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This commit is contained in:
Manav Rathi
2025-04-29 13:27:48 +05:30
parent b1efd289d3
commit 94de25cb26
2 changed files with 58 additions and 46 deletions
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99
desktop/src/main/services/ffmpeg.ts
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@@ -145,10 +145,10 @@ export interface FFmpegGenerateHLSPlaylistAndSegmentsResult {
*
* Overview of the cases:
*
* H.264, <= 10 MB - Skip
* H.264, <= 4000 kb/s bitrate - Don't re-encode video stream
* <= 2000 kb/s bitrate - Don't apply the scale+fps filter
* !BT.709 - Apply tonemap (zscale+tonemap+zscale)
* H.264, <= 10 MB - Skip
* H.264, <= 4000 kb/s bitrate - Don't re-encode video stream
* BT.709, <= 2000 kb/s bitrate - Don't apply the scale+fps filter
* !BT.709 - Apply tonemap (zscale+tonemap+zscale)
*
* Example invocation:
*
@@ -174,41 +174,6 @@ export const ffmpegGenerateHLSPlaylistAndSegments = async (
inputFilePath: string,
outputPathPrefix: string,
): Promise<FFmpegGenerateHLSPlaylistAndSegmentsResult | undefined> => {
// [Note: Tonemapping HDR to HD]
//
// BT.709 ("HD") is a standard that describes things like how color is
// encoded, the range of values, and their "meaning" - i.e. how to map the
// values in the video to the pixels on the screen.
//
// It is not the only such standard, there are three common examples:
//
// - BT.601 ("Standard-Definition" or SD)
// - BT.709 ("High-Definition" or HD)
// - BT.2020 ("Ultra-High-Definition" or UHD, aka HDR^).
//
// ^ HDR ("High-Dynamic-Range") is an addendum to BT.2020, but for our
// 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 (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
// possible hardware/OS/browser combinations.
//
// If we convert HDR to HD without naively, then the colors look washed out
// compared to the original. To resolve this, we use a ffmpeg filterchain
// that uses the tonemap filter.
//
// However applying this tonemap to videos that are already HD leads to a
// 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
const { isH264, isBT709, bitrate } =
await detectVideoCharacteristics(inputFilePath);
@@ -253,6 +218,43 @@ export const ffmpegGenerateHLSPlaylistAndSegments = async (
// but more for avoiding making the video size smaller unnecessarily.
const rescaleVideo = !(bitrate && bitrate <= 2000 * 1000);
// [Note: Tonemapping HDR to HD]
//
// BT.709 ("HD") is a standard that describes things like how color is
// encoded, the range of values, and their "meaning" - i.e. how to map the
// values in the video to the pixels on the screen.
//
// It is not the only such standard, there are three common examples:
//
// - BT.601 ("Standard-Definition" or SD)
// - BT.709 ("High-Definition" or HD)
// - BT.2020 ("Ultra-High-Definition" or UHD, aka HDR^).
//
// ^ HDR ("High-Dynamic-Range") is an addendum to BT.2020, but for our
// 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 (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
// possible hardware/OS/browser combinations.
//
// If we convert HDR to HD without naively, then the colors look washed out
// compared to the original. To resolve this, we use a ffmpeg filterchain
// that uses the tonemap filter.
//
// However applying this tonemap to videos that are already HD leads to a
// 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
const tonemap = !isBT709;
// We want the generated playlist to refer to the chunks as "output.ts".
//
// So we arrange things accordingly: We use the `outputPathPrefix` as our
@@ -314,7 +316,16 @@ export const ffmpegGenerateHLSPlaylistAndSegments = async (
// `filter1=key=value:key=value.filter2=key=value`.
"-vf",
[
rescaleVideo
// Do the rescaling to even number of pixels always if the
// tonemapping is going to be applied subsequently,
// otherwise the tonemapping will fail with "image
// dimensions must be divisible by subsampling factor".
//
// While we add the extra condition here for completeness,
// it won't usually matter since a non-BT.709 video is
// likely using a new codec, and as such would've a high
// enough bitrate to require rescaling anyways.
rescaleVideo || tonemap
? [
// Scales the video to maximum 720p height,
// keeping aspect ratio and the calculated
@@ -348,13 +359,13 @@ export const ffmpegGenerateHLSPlaylistAndSegments = async (
// See: https://ffmpeg.org/ffmpeg-filters.html#tonemap-1
//
// See: [Note: Tonemapping HDR to HD]
isBT709
? []
: [
tonemap
? [
"zscale=transfer=linear",
"tonemap=tonemap=hable:desat=0",
"zscale=primaries=709:transfer=709:matrix=709",
],
]
: [],
// Output using the well supported pixel format: 8-bit YUV
// planar color space with 4:2:0 chroma subsampling.
"format=yuv420p",