When encoding VP9 with a YUV pixel format (e.g. yuv420p) and
AVCOL_SPC_RGB colorspace metadata, libvpxenc unconditionally set
VPX_CS_SRGB. This produced a spec-violating bitstream: Profile 0
(4:2:0) with sRGB colorspace, which is only valid for Profile 1/3
(4:4:4). The resulting file is undecodable.
Fix this by setting ctx->vpx_cs to VPX_CS_SRGB in set_pix_fmt()
for 4:4:4 YUV formats when AVCOL_SPC_RGB is set, matching the
existing GBRP path. This covers the legitimate case of RGB data in
YUV444 containers (e.g. H.264 High 4:4:4 with identity matrix).
With this change, any AVCOL_SPC_RGB that reaches the switch in
set_colorspace() is guaranteed to be a subsampled format where
sRGB is invalid. Log a warning and fall back to VPX_CS_BT_709.
To reproduce:
# generate a bad source
ffmpeg -f lavfi -i testsrc=s=64x64:d=1:r=1 \
-pix_fmt yuv420p -colorspace rgb bad.mp4
# transcode with default parameters
ffmpeg -i bad.mp4 bad.webm
# check decoding
ffmpeg -i bad.webm -f null -
# -> 0 frames decoded, error
Signed-off-by: Guangyu Sun <[email protected]>
---
v2:
- Only fall back to BT.709 if the pixel format is not 4:4:4,
addressing feedback regarding Profile 1/3 support.
libavcodec/libvpxenc.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/libavcodec/libvpxenc.c b/libavcodec/libvpxenc.c
index 082709c41f..fd80d7ca04 100644
--- a/libavcodec/libvpxenc.c
+++ b/libavcodec/libvpxenc.c
@@ -835,6 +835,8 @@ static int set_pix_fmt(AVCodecContext *avctx,
vpx_codec_caps_t codec_caps,
case AV_PIX_FMT_GBRP:
ctx->vpx_cs = VPX_CS_SRGB;
case AV_PIX_FMT_YUV444P:
+ if (avctx->colorspace == AVCOL_SPC_RGB)
+ ctx->vpx_cs = VPX_CS_SRGB;
enccfg->g_profile = 1;
*img_fmt = VPX_IMG_FMT_I444;
return 0;
@@ -870,6 +872,8 @@ static int set_pix_fmt(AVCodecContext *avctx,
vpx_codec_caps_t codec_caps,
ctx->vpx_cs = VPX_CS_SRGB;
case AV_PIX_FMT_YUV444P10:
case AV_PIX_FMT_YUV444P12:
+ if (avctx->colorspace == AVCOL_SPC_RGB)
+ ctx->vpx_cs = VPX_CS_SRGB;
if (codec_caps & VPX_CODEC_CAP_HIGHBITDEPTH) {
enccfg->g_profile = 3;
*img_fmt = VPX_IMG_FMT_I44416;
@@ -893,7 +897,17 @@ static void set_colorspace(AVCodecContext *avctx)
vpx_cs = ctx->vpx_cs;
} else {
switch (avctx->colorspace) {
- case AVCOL_SPC_RGB: vpx_cs = VPX_CS_SRGB; break;
+ case AVCOL_SPC_RGB:
+ // All sRGB-compatible formats (GBRP*, and YUV444* with
+ // AVCOL_SPC_RGB) set ctx->vpx_cs in set_pix_fmt() and
+ // take the branch above, so reaching here means a
+ // subsampled format incompatible with RGB colorspace.
+ av_log(avctx, AV_LOG_WARNING,
+ "RGB colorspace is not compatible with pixel format %s, "
+ "using BT.709 instead.\n",
+ av_get_pix_fmt_name(avctx->pix_fmt));
+ vpx_cs = VPX_CS_BT_709;
+ break;
case AVCOL_SPC_BT709: vpx_cs = VPX_CS_BT_709; break;
case AVCOL_SPC_UNSPECIFIED: vpx_cs = VPX_CS_UNKNOWN; break;
case AVCOL_SPC_RESERVED: vpx_cs = VPX_CS_RESERVED; break;
--
2.52.0
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