From: Steinar H. Gunderson <sgunderson@bigfoot.com>
Date: Sun, 1 Nov 2015 17:06:23 +0000 (+0100)
Subject: Specify unspecified gamma instead of lying and saying we use Rec. 709. Again, for... 
X-Git-Tag: 1.0.0~183
X-Git-Url: https://git.sesse.net/?p=nageru;a=commitdiff_plain;h=be250b0bb36e5cca60feb810461c116495bcc357

Specify unspecified gamma instead of lying and saying we use Rec. 709. Again, for the benefit of icky players.
---

diff --git a/h264encode.cpp b/h264encode.cpp
index 4b900bf..74b5191 100644
--- a/h264encode.cpp
+++ b/h264encode.cpp
@@ -347,7 +347,7 @@ static void sps_rbsp(bitstream *bs)
             bitstream_put_ui(bs, 1, 1);  /* colour_description_present_flag */
             {
                 bitstream_put_ui(bs, 1, 8);  /* colour_primaries (1 = BT.709) */
-                bitstream_put_ui(bs, 1, 8);  /* transfer_characteristics (1 = BT.709) */
+                bitstream_put_ui(bs, 2, 8);  /* transfer_characteristics (2 = unspecified, since we use sRGB) */
                 bitstream_put_ui(bs, 6, 8);  /* matrix_coefficients (6 = BT.601/SMPTE 170M) */
             }
         }
diff --git a/httpd.cpp b/httpd.cpp
index 5721884..f266c63 100644
--- a/httpd.cpp
+++ b/httpd.cpp
@@ -94,7 +94,7 @@ HTTPD::Mux::Mux(AVFormatContext *avctx, int width, int height)
 	// Note that the H.264 stream also contains this information and depending on the
 	// mux, this might simply get ignored. See sps_rbsp().
 	avstream_video->codec->color_primaries = AVCOL_PRI_BT709;  // RGB colorspace (inout_format.color_space).
-	avstream_video->codec->color_trc = AVCOL_TRC_BT709;  // Gamma curve (inout_format.gamma_curve).
+	avstream_video->codec->color_trc = AVCOL_TRC_UNSPECIFIED;  // Gamma curve (inout_format.gamma_curve).
 	avstream_video->codec->colorspace = AVCOL_SPC_SMPTE170M;  // YUV colorspace (output_ycbcr_format.luma_coefficients).
 	avstream_video->codec->color_range = AVCOL_RANGE_MPEG;  // Full vs. limited range (output_ycbcr_format.full_range).
 	avstream_video->codec->chroma_sample_location = AVCHROMA_LOC_LEFT;  // Chroma sample location. See chroma_offset_0[] in Mixer::subsample_chroma().
diff --git a/theme.cpp b/theme.cpp
index 2c9af01..9914952 100644
--- a/theme.cpp
+++ b/theme.cpp
@@ -129,12 +129,10 @@ int EffectChain_finalize(lua_State* L)
 	ImageFormat inout_format;
 	inout_format.color_space = COLORSPACE_REC_709;
 
-	// Gamma curve depends on the input signal, and we don't really get any
-	// indications. A camera would be expected to do Rec. 709, but
-	// I haven't checked if any do in practice. However, computers _do_ output
-	// in sRGB gamma (ie., they don't convert from sRGB to Rec. 709), and
-	// I wouldn't really be surprised if most non-professional cameras do, too.
-	// So we pick sRGB as the least evil here.
+	// Output gamma is tricky. We should output Rec. 709 for TV, except that
+	// we expect to run with web players and others that don't really care and
+	// just output with no conversion. So that means we'll need to output sRGB,
+	// even though H.264 has no setting for that (we use “unspecified”).
 	inout_format.gamma_curve = GAMMA_sRGB;
 
 	if (is_main_chain) {
@@ -337,6 +335,13 @@ LiveInputWrapper::LiveInputWrapper(Theme *theme, EffectChain *chain, bool overri
 {
 	ImageFormat inout_format;
 	inout_format.color_space = COLORSPACE_sRGB;
+
+	// Gamma curve depends on the input signal, and we don't really get any
+	// indications. A camera would be expected to do Rec. 709, but
+	// I haven't checked if any do in practice. However, computers _do_ output
+	// in sRGB gamma (ie., they don't convert from sRGB to Rec. 709), and
+	// I wouldn't really be surprised if most non-professional cameras do, too.
+	// So we pick sRGB as the least evil here.
 	inout_format.gamma_curve = GAMMA_sRGB;
 
 	// The Blackmagic driver docs claim that the device outputs Y'CbCr