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av1decoder: Fix multiplication wraparound

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The GstAV1Picture system_frame_number is guint32, constant 1000 is guint32,
GstV4l2CodecAV1Dec v4l2_av1_frame.*_frame_ts multiplication result is u64 .

```
u64 result = (u32)((u32)system_frame_number * (u32)1000);
```
behaves the same as
```
u64 result = (u32)(((u32)system_frame_number * (u32)1000) & 0xffffffff);
```

so in case `system_frame_number > 4294967295 / 1000`, the `result` will
wrap around. Since the `result` is really used as a cookie used to look
up V4L2 buffers related to the currently decoded frame, this wraparound
leads to visible corruption during AV1 decoding. At 30 FPS this occurs
after cca. 40 hours of playback .

Fix this by changing the 1000 from u32 to u64, i.e.:
```
u64 result = (u64)((u32)system_frame_number * (u64)1000ULL);
```
this way, the wraparound is prevented and the correct cookie is used.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5791>
This commit is contained in:
Marek Vasut 2023-12-09 16:24:22 +01:00 committed by GStreamer Marge Bot
parent 6f74818a07
commit 50fb6f8c02
1 changed files with 1 additions and 1 deletions
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2
subprojects/gst-plugins-bad/sys/v4l2codecs/gstv4l2codecav1dec.c
View file

@ -547,7 +547,7 @@ gst_v4l2_codec_av1_fill_refs (GstV4l2CodecAV1Dec * self,
/* the decoder might not have filled all slots in the first few frames */ /* the decoder might not have filled all slots in the first few frames */
self->v4l2_frame.reference_frame_ts[i] = self->v4l2_frame.reference_frame_ts[i] =
ref_pic ? GST_CODEC_PICTURE_FRAME_NUMBER (ref_pic) * 1000 : 0; ref_pic ? GST_CODEC_PICTURE_FRAME_NUMBER (ref_pic) * G_GUINT64_CONSTANT (1000) : 0;
} }
memcpy (self->v4l2_frame.ref_frame_idx, frame_hdr->ref_frame_idx, memcpy (self->v4l2_frame.ref_frame_idx, frame_hdr->ref_frame_idx,