[FFmpeg-devel] [PATCH v2] avcodec/cbs_vp8: Improve the bitstream position check

[FFmpeg-devel] [PATCH v2] avcodec/cbs_vp8: Improve the bitstream position check

[Dai, Jianhui J]

The VP8 compressed header may not be byte-aligned due to boolean
coding. Round up byte count for accurate data positioning.

Signed-off-by: Jianhui Dai <jianhui.j.dai@intel.com>
---
 libavcodec/cbs_vp8.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/libavcodec/cbs_vp8.c b/libavcodec/cbs_vp8.c
index 1f7e81cfe6..bb441b7187 100644
--- a/libavcodec/cbs_vp8.c
+++ b/libavcodec/cbs_vp8.c
@@ -328,7 +328,9 @@ static int cbs_vp8_read_unit(CodedBitstreamContext *ctx,
         return err;
 
     pos = get_bits_count(&gbc);
-    pos /= 8;
+    // Position may not be byte-aligned after compressed header; Round up byte
+    // count for accurate data positioning.
+    pos = (pos + 7) / 8;
     av_assert0(pos <= unit->data_size);
 
     frame->data_ref = av_buffer_ref(unit->data_ref);
-- 
2.34.1

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Re: [FFmpeg-devel] [PATCH v2] avcodec/cbs_vp8: Improve the bitstream position check

[Ronald S. Bultje]

Hi,

On Tue, Mar 19, 2024 at 2:05 AM Dai, Jianhui J <
jianhui.j.dai-at-intel.com@ffmpeg.org> wrote:

> The VP8 compressed header may not be byte-aligned due to boolean
> coding. Round up byte count for accurate data positioning.
>
> Signed-off-by: Jianhui Dai <jianhui.j.dai@intel.com>
> ---
>  libavcodec/cbs_vp8.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/libavcodec/cbs_vp8.c b/libavcodec/cbs_vp8.c
> index 1f7e81cfe6..bb441b7187 100644
> --- a/libavcodec/cbs_vp8.c
> +++ b/libavcodec/cbs_vp8.c
> @@ -328,7 +328,9 @@ static int cbs_vp8_read_unit(CodedBitstreamContext
> *ctx,
>          return err;
>
>      pos = get_bits_count(&gbc);
> -    pos /= 8;
> +    // Position may not be byte-aligned after compressed header; Round up
> byte
> +    // count for accurate data positioning.
> +    pos = (pos + 7) / 8;
>      av_assert0(pos <= unit->data_size);
>
>      frame->data_ref = av_buffer_ref(unit->data_ref);
> --
> 2.34.1
>

Merged.

Ronald
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