[meh7an]

Based on #31406, which adds the tone mapping this uses; only the last commit is new here.

When an HDR video is sent, the send box preview and the uploaded thumbnail (the clip reader), the video timeline in the photo editor and the re-encode used for a reduced quality or trimmed video all convert frames with plain swscale. The preview and timeline are washed out, and the re-encoded file is written as 8-bit SDR samples while it keeps the PQ or HLG tags of the source, so it looks broken for everyone who receives it.

These paths now go through one helper, Streaming::ConvertFrameToARGB32(), which tone maps HDR frames the same way playback does and runs swscale for the rest. The re-encode tone maps HDR frames to SDR before encoding and tags the result with what it is: the BT.709 transfer, the SMPTE 170M matrix because swscale converts RGB to YUV with BT.601 coefficients, and BT.709 primaries, or the source primaries when they are not BT.2020, because only BT.2020 is converted.

Testing

Tested on macOS 27.0, in a Debug build, with an 8-bit HLG video recorded on an iPhone:

• The send box preview and the video timeline in the photo editor show correct colors instead of washed out.
• Sending it with reduced quality uploads a video that plays with correct colors.
• Temporary code re-encoded HDR10 and HLG test videos at a smaller size: the output is tagged BT.709 with the SMPTE 170M matrix and decodes to the colors of the tone mapped source, 1 to 3 levels apart in the median.

[john-preston]

It inherits #31406’s alpha loss and can permanently remove transparency from generated stickers.

[meh7an]

It inherits #31406’s alpha loss and can permanently remove transparency from generated stickers.

Thanks, fixed in #31406's commit, so #31407 and #31408 get it too. HDR frames with an alpha plane are now tone mapped through YUVA420P10 instead of P010, and the alpha is copied back into the tone mapped image, so they keep their transparency like SDR frames do. Checked with an HDR-tagged VP9 webm with alpha: the send box preview and playback now show it with transparency, the same as the same file without the HDR tags.