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encoder: h264: improve automatic bitrate calculation.

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For non "Constant-QP" modes, we could provide more reasonable heuristics
for the target bitrate. In general, 48 bits per macroblock with all the
useful coding tools enable looks safe enough. Then, this rate is raised
by +10% to +15% for each coding tool that is disabled.

https://bugzilla.gnome.org/show_bug.cgi?id=719699
This commit is contained in:
Gwenole Beauchesne 2014-01-13 11:49:14 +01:00
parent 7b1233faa8
commit c7a2095b78
1 changed files with 17 additions and 5 deletions
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22
gst-libs/gst/vaapi/gstvaapiencoder_h264.c
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@ -1360,16 +1360,28 @@ ensure_bitrate (GstVaapiEncoderH264 * encoder)
{
GstVaapiEncoder *const base_encoder = GST_VAAPI_ENCODER_CAST (encoder);
/* Default compression: 64 bits per macroblock */
/* Default compression: 48 bits per macroblock in "high-compression" mode */
switch (GST_VAAPI_ENCODER_RATE_CONTROL (encoder)) {
case GST_VAAPI_RATECONTROL_CBR:
case GST_VAAPI_RATECONTROL_VBR:
case GST_VAAPI_RATECONTROL_VBR_CONSTRAINED:
if (!base_encoder->bitrate)
base_encoder->bitrate = GST_VAAPI_ENCODER_WIDTH (encoder) *
GST_VAAPI_ENCODER_HEIGHT (encoder) *
if (!base_encoder->bitrate) {
/* According to the literature and testing, CABAC entropy coding
mode could provide for +10% to +18% improvement in general,
thus estimating +15% here ; and using adaptive 8x8 transforms
in I-frames could bring up to +10% improvement. */
guint bits_per_mb = 48;
if (!encoder->use_cabac)
bits_per_mb += (bits_per_mb * 15) / 100;
if (!encoder->use_dct8x8)
bits_per_mb += (bits_per_mb * 10) / 100;
base_encoder->bitrate =
encoder->mb_width * encoder->mb_height * bits_per_mb *
GST_VAAPI_ENCODER_FPS_N (encoder) /
GST_VAAPI_ENCODER_FPS_D (encoder) / 4 / 1000;
GST_VAAPI_ENCODER_FPS_D (encoder) / 1000;
GST_INFO ("target bitrate computed to %u kbps", base_encoder->bitrate);
}
break;
default:
base_encoder->bitrate = 0;