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Encode alpha as 4:2:0 with SVT #2004

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Feb 12, 2024
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Encode alpha as 4:2:0 with SVT #2004

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32 changes: 30 additions & 2 deletions src/codec_svt.c
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@

#include "svt-av1/EbSvtAv1Enc.h"

#include <stdint.h>
#include <string.h>

// The SVT_AV1_VERSION_MAJOR, SVT_AV1_VERSION_MINOR, SVT_AV1_VERSION_PATCHLEVEL, and
Expand Down Expand Up @@ -76,6 +77,7 @@ static avifResult svtCodecEncodeImage(avifCodec * codec,

avifResult result = AVIF_RESULT_UNKNOWN_ERROR;
EbColorFormat color_format = EB_YUV420;
uint8_t * uvPlanes = NULL; // 4:2:0 U and V placeholder for alpha because SVT-AV1 does not support 4:0:0.
EbBufferHeaderType * input_buffer = NULL;
EbErrorType res = EB_ErrorNone;

Expand All @@ -98,6 +100,7 @@ static avifResult svtCodecEncodeImage(avifCodec * codec,
y_shift = 1;
break;
case AVIF_PIXEL_FORMAT_YUV400:
// Setting color_format = EB_YUV400; results in "Svt[error]: Instance 1: Only support 420 now".
case AVIF_PIXEL_FORMAT_NONE:
case AVIF_PIXEL_FORMAT_COUNT:
default:
Expand Down Expand Up @@ -198,16 +201,38 @@ static avifResult svtCodecEncodeImage(avifCodec * codec,
}
EbSvtIOFormat * input_picture_buffer = (EbSvtIOFormat *)input_buffer->p_buffer;

int bytesPerPixel = image->depth > 8 ? 2 : 1;
const uint32_t bytesPerPixel = image->depth > 8 ? 2 : 1;
const uint32_t uvHeight = (image->height + y_shift) >> y_shift;
if (alpha) {
input_picture_buffer->y_stride = image->alphaRowBytes / bytesPerPixel;
input_picture_buffer->luma = image->alphaPlane;
input_buffer->n_filled_len = image->alphaRowBytes * image->height;

#if SVT_AV1_CHECK_VERSION(1, 8, 0)
// Simulate 4:2:0 UV planes. SVT-AV1 does not support 4:0:0 samples.
const uint32_t uvWidth = (image->width + y_shift) >> y_shift;
const uint32_t uvRowBytes = uvWidth * bytesPerPixel;
const uint32_t uvSize = uvRowBytes * uvHeight;
uvPlanes = avifAlloc(uvSize);
if (uvPlanes == NULL) {
goto cleanup;
}
memset(uvPlanes, 0, uvSize);
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Optional: It would be "realistic" to set the uvPlanes buffer to the neutral value (8-bit: 128; 10-bit: 512; 12-bit: 2048), corresponding to 0.5. But we can't use memset to do that for high bit depths. Given that the AVIF decoders will ignore the UV planes in the alpha auxiliary image, I think it is fine to just set the uvPlanes buffer to 0.

input_picture_buffer->cb = uvPlanes;
input_buffer->n_filled_len += uvSize;
input_picture_buffer->cr = uvPlanes;
input_buffer->n_filled_len += uvSize;
input_picture_buffer->cb_stride = uvWidth;
input_picture_buffer->cr_stride = uvWidth;
#else
// This workaround was not needed before SVT-AV1 1.8.0.
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It is unusual that older versions work better. Do you know why?

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No. I asked about it here but got no answer.

// See https://github.com/AOMediaCodec/libavif/issues/1992.
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It seems better to reference the SVT-AV1 bug report instead: https://gitlab.com/AOMediaCodec/SVT-AV1/-/issues/2146

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The two are referencing each other, and we have more control on a GitHub issue than on a GitLab issue. If someone looks into that again, they can easily find the two reports.

(void)uvPlanes;
#endif
} else {
input_picture_buffer->y_stride = image->yuvRowBytes[0] / bytesPerPixel;
input_picture_buffer->luma = image->yuvPlanes[0];
input_buffer->n_filled_len = image->yuvRowBytes[0] * image->height;
uint32_t uvHeight = (image->height + y_shift) >> y_shift;
input_picture_buffer->cb = image->yuvPlanes[1];
input_buffer->n_filled_len += image->yuvRowBytes[1] * uvHeight;
input_picture_buffer->cr = image->yuvPlanes[2];
Expand All @@ -232,6 +257,9 @@ static avifResult svtCodecEncodeImage(avifCodec * codec,

result = dequeue_frame(codec, output, AVIF_FALSE);
cleanup:
if (uvPlanes) {
avifFree(uvPlanes);
}
if (input_buffer) {
if (input_buffer->p_buffer) {
avifFree(input_buffer->p_buffer);
Expand Down
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