[FFmpeg-devel] PATCH: Fallback to NV12 format in VAAPI drivers

[Lluís Batlle i Rossell]

On Fri, Aug 09, 2024 at 09:43:53AM +0200, Lluís Batlle i Rossell wrote:
> On Fri, Aug 09, 2024 at 11:49:54AM +0800, Zhao Zhili wrote:
> > > vaapi drivers often lack proper image converesions and not all
> > > situations allow vagetimage or vaputimage with the image formats
> > > reported by the api. nv12 seems allowed in all circumstances.
> > > 
> > > with this change now one can use the hwaccel directly without
> > > explicit conversions to nv12 for frame downloading to work.
> > > 
> > > gstreamer adopted a similar approach:
> > > https://bugzilla.gnome.org/show_bug.cgi?id=752958
> > 
> > Isn’t it break all pixel formats with bit depth > 8?
> > I think we already have hwcontext API to select sw_format, this isn’t a bug
> > inside ffmpeg.
> 
> Correct... I didn't think of the need beyond NV12.
> 
> What if I redo the patch so I keep all formats, but I simply move NV12 to
> the first place? That will make ffmpeg pick NV12 as default if NONE
> specified.

I attach a different patch, so NV12 is only picked in case the dst format
is NONE.
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>From c633b6ba0975bd495df2479aa9a562958bb87e59 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Llu=C3=ADs=20Batlle=20i=20Rossell?= <viric at viric.name>
Date: Sat, 10 Aug 2024 10:45:14 +0200
Subject: [PATCH] Fallback to NV12 format in VAAPI drivers

Even if the hw format is listed in the supported ImageFormats. That's
because some drivers fail in vaGetImage even if requesting the transfer
in a format equal to the hw format.

NV12 is chosen only if the users don't specify any other particular
format.

gstreamer adopted a similar approach:
https://bugzilla.gnome.org/show_bug.cgi?id=752958
---
 libavutil/hwcontext_vaapi.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/libavutil/hwcontext_vaapi.c b/libavutil/hwcontext_vaapi.c
index 12bc95119a..0396038017 100644
--- a/libavutil/hwcontext_vaapi.c
+++ b/libavutil/hwcontext_vaapi.c
@@ -720,20 +720,22 @@ static int vaapi_transfer_get_formats(AVHWFramesContext *hwfc,
 {
     VAAPIDeviceContext *ctx = hwfc->device_ctx->internal->priv;
     enum AVPixelFormat *pix_fmts;
-    int i, k, sw_format_available;
+    int i, k, nv12_format_available;
 
-    sw_format_available = 0;
+    /* Intel VAAPI drivers seem to support NV12 for vaGetImage,
+     * but fail for many formats announced in vaQueryImageFormats */
+    nv12_format_available = 0;
     for (i = 0; i < ctx->nb_formats; i++) {
-        if (ctx->formats[i].pix_fmt == hwfc->sw_format)
-            sw_format_available = 1;
+        if (ctx->formats[i].pix_fmt == AV_PIX_FMT_NV12)
+            nv12_format_available = 1;
     }
 
     pix_fmts = av_malloc((ctx->nb_formats + 1) * sizeof(*pix_fmts));
     if (!pix_fmts)
         return AVERROR(ENOMEM);
 
-    if (sw_format_available) {
-        pix_fmts[0] = hwfc->sw_format;
+    if (nv12_format_available) {
+        pix_fmts[0] = AV_PIX_FMT_NV12;
         k = 1;
     } else {
         k = 0;
-- 
2.44.1