bool is_main_chain = checkbool(L, 2);
// Add outputs as needed.
+ // NOTE: If you change any details about the output format, you will need to
+ // also update what's given to the muxer (HTTPD::Mux constructor) and
+ // what's put in the H.264 stream (sps_rbsp()).
ImageFormat inout_format;
- inout_format.color_space = COLORSPACE_sRGB;
+ inout_format.color_space = COLORSPACE_REC_709;
+
+ // 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) {
YCbCrFormat output_ycbcr_format;
+ // We actually output 4:2:0 in the end, but chroma subsampling
+ // happens in a pass not run by Movit (see Mixer::subsample_chroma()).
output_ycbcr_format.chroma_subsampling_x = 1;
output_ycbcr_format.chroma_subsampling_y = 1;
- output_ycbcr_format.luma_coefficients = YCBCR_REC_709;
+
+ // Rec. 709 would be the sane thing to do, but it seems many players
+ // (e.g. MPlayer and VLC) just default to BT.601 coefficients no matter
+ // what (see discussions in e.g. https://trac.ffmpeg.org/ticket/4978).
+ // We _do_ set the right flags, though, so that a player that works
+ // properly doesn't have to guess.
+ output_ycbcr_format.luma_coefficients = YCBCR_REC_601;
output_ycbcr_format.full_range = false;
+ output_ycbcr_format.num_levels = 256;
chain->add_ycbcr_output(inout_format, OUTPUT_ALPHA_FORMAT_POSTMULTIPLIED, output_ycbcr_format, YCBCR_OUTPUT_SPLIT_Y_AND_CBCR);
chain->set_dither_bits(8);
{
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
+ // according to Rec. 601, but practical testing indicates it definitely
+ // is Rec. 709 (at least up to errors attributable to rounding errors).
+ // Perhaps 601 was only to indicate the subsampling positions, not the
+ // colorspace itself? Tested with a Lenovo X1 gen 3 as input.
YCbCrFormat input_ycbcr_format;
input_ycbcr_format.chroma_subsampling_x = 2;
input_ycbcr_format.chroma_subsampling_y = 1;
input_ycbcr_format.cr_x_position = 0.0;
input_ycbcr_format.cb_y_position = 0.5;
input_ycbcr_format.cr_y_position = 0.5;
- input_ycbcr_format.luma_coefficients = YCBCR_REC_601;
+ input_ycbcr_format.luma_coefficients = YCBCR_REC_709;
input_ycbcr_format.full_range = false;
if (override_bounce) {