* [FFmpeg-devel] [PATCH] libavcodec/v4l2_buffers: fixing buffer alignment issue
@ 2025-11-13 3:29 Wenjie Yin via ffmpeg-devel
2025-11-13 6:56 ` [FFmpeg-devel] " Zhao Zhili via ffmpeg-devel
0 siblings, 1 reply; 2+ messages in thread
From: Wenjie Yin via ffmpeg-devel @ 2025-11-13 3:29 UTC (permalink / raw)
To: ffmpeg-devel, Wenjie Yin
Cc: wangao.wang, Qiwei Liu (QUIC), renjiang.han, Wenjie Yin
V4l2 drivers may return buffer width & height with aligned values, which
may be different from frame width & height. Bytesperlines and strides
should be check for aligned buffers when copying pixel data. When width
aligned, copy with planar; otherwise, copy line-by-line to dest buffer.
Co-authored-by: Renjiang Han <renjiang.han@oss.qualcomm.com>
Signed-off-by: Wenjie.Yin <quic_wenjyin@quicinc.com>
Signed-off-by: Wenjie Yin <wenjyin@qti.qualcomm.com>
---
libavcodec/v4l2_buffers.c | 68 +++++++++++++++++++++++++++++++++++----
1 file changed, 62 insertions(+), 6 deletions(-)
diff --git a/libavcodec/v4l2_buffers.c b/libavcodec/v4l2_buffers.c
index d869ce9e77..5f5a8aefd5 100644
--- a/libavcodec/v4l2_buffers.c
+++ b/libavcodec/v4l2_buffers.c
@@ -356,6 +356,33 @@ static int v4l2_buffer_buf_to_swframe(AVFrame *frame, V4L2Buffer *avbuf)
return 0;
}
+static int v4l2_plane_to_plane_align(V4L2Buffer *out, int plane, const uint8_t* data, int size, int offset, int width, int height, int stride)
+{
+ unsigned int bytesused, length;
+
+ if (plane >= out->num_planes)
+ return AVERROR(EINVAL);
+
+ length = out->plane_info[plane].length;
+ bytesused = FFMIN(size+offset, length);
+
+ for (int i = 0; i < height; i++) {
+ memcpy((uint8_t*)out->plane_info[plane].mm_addr + offset, data, width);
+ offset += stride;
+ data += width;
+ }
+
+ if (V4L2_TYPE_IS_MULTIPLANAR(out->buf.type)) {
+ out->planes[plane].bytesused = bytesused;
+ out->planes[plane].length = length;
+ } else {
+ out->buf.bytesused = bytesused;
+ out->buf.length = length;
+ }
+
+ return 0;
+}
+
static int v4l2_buffer_swframe_to_buf(const AVFrame *frame, V4L2Buffer *out)
{
int i, ret;
@@ -364,7 +391,11 @@ static int v4l2_buffer_swframe_to_buf(const AVFrame *frame, V4L2Buffer *out)
fmt.fmt.pix_mp.pixelformat : fmt.fmt.pix.pixelformat;
int height = V4L2_TYPE_IS_MULTIPLANAR(fmt.type) ?
fmt.fmt.pix_mp.height : fmt.fmt.pix.height;
- int is_planar_format = 0;
+ int bytesperline = V4L2_TYPE_IS_MULTIPLANAR(fmt.type) ?
+ (fmt.fmt.pix_mp.num_planes ? fmt.fmt.pix_mp.plane_fmt[0].bytesperline: 0) : fmt.fmt.pix.bytesperline;
+ int sizeimage = V4L2_TYPE_IS_MULTIPLANAR(fmt.type) ?
+ (fmt.fmt.pix_mp.num_planes ? fmt.fmt.pix_mp.plane_fmt[0].sizeimage: 0) : fmt.fmt.pix.sizeimage;
+ int is_planar_format = 0, scanline_y = 0, scanline_uv = 0;
switch (pixel_format) {
case V4L2_PIX_FMT_YUV420M:
@@ -398,16 +429,41 @@ static int v4l2_buffer_swframe_to_buf(const AVFrame *frame, V4L2Buffer *out)
for (i = 0; i < desc->nb_components; i++)
planes_nb = FFMAX(planes_nb, desc->comp[i].plane + 1);
+ switch (pixel_format)
+ {
+ /* Currently only NV12 & NV21 are addressed for buffer alignment issue */
+ case V4L2_PIX_FMT_NV12:
+ case V4L2_PIX_FMT_NV21:
+ scanline_y = sizeimage / bytesperline * 2 / 3;
+ scanline_uv = scanline_y / 2;
+ break;
+ default:
+ /* By default, no buffer alignment issues are expected */
+ scanline_y = height;
+ scanline_uv = AV_CEIL_RSHIFT(height, desc->log2_chroma_h);
+ bytesperline = frame->linesize[0];
+ break;
+ }
+
for (i = 0; i < planes_nb; i++) {
int size, h = height;
if (i == 1 || i == 2) {
h = AV_CEIL_RSHIFT(h, desc->log2_chroma_h);
}
- size = frame->linesize[i] * h;
- ret = v4l2_bufref_to_buf(out, 0, frame->data[i], size, offset);
- if (ret)
- return ret;
- offset += size;
+
+ if (bytesperline == frame->linesize[0]) {
+ size = frame->linesize[i] * h;
+ ret = v4l2_bufref_to_buf(out, 0, frame->data[i], size, offset);
+ if (ret)
+ return ret;
+ offset += frame->linesize[i] * (i ? scanline_uv : scanline_y);
+ } else {
+ size = bytesperline * (i ? scanline_uv : scanline_y);
+ ret = v4l2_plane_to_plane_align(out, 0, frame->data[i], size, offset, frame->linesize[i], h, bytesperline);
+ if (ret)
+ return ret;
+ offset += size;
+ }
}
return 0;
}
--
2.34.1
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^ permalink raw reply [flat|nested] 2+ messages in thread
* [FFmpeg-devel] Re: [PATCH] libavcodec/v4l2_buffers: fixing buffer alignment issue
2025-11-13 3:29 [FFmpeg-devel] [PATCH] libavcodec/v4l2_buffers: fixing buffer alignment issue Wenjie Yin via ffmpeg-devel
@ 2025-11-13 6:56 ` Zhao Zhili via ffmpeg-devel
0 siblings, 0 replies; 2+ messages in thread
From: Zhao Zhili via ffmpeg-devel @ 2025-11-13 6:56 UTC (permalink / raw)
To: FFmpeg development discussions and patches
Cc: Wenjie Yin, wangao.wang, Qiwei Liu (QUIC), renjiang.han, Zhao Zhili
> On Nov 13, 2025, at 11:29, Wenjie Yin via ffmpeg-devel <ffmpeg-devel@ffmpeg.org> wrote:
>
> V4l2 drivers may return buffer width & height with aligned values, which
> may be different from frame width & height. Bytesperlines and strides
> should be check for aligned buffers when copying pixel data. When width
> aligned, copy with planar; otherwise, copy line-by-line to dest buffer.
>
> Co-authored-by: Renjiang Han <renjiang.han@oss.qualcomm.com>
> Signed-off-by: Wenjie.Yin <quic_wenjyin@quicinc.com>
> Signed-off-by: Wenjie Yin <wenjyin@qti.qualcomm.com>
> ---
> libavcodec/v4l2_buffers.c | 68 +++++++++++++++++++++++++++++++++++----
> 1 file changed, 62 insertions(+), 6 deletions(-)
>
> diff --git a/libavcodec/v4l2_buffers.c b/libavcodec/v4l2_buffers.c
> index d869ce9e77..5f5a8aefd5 100644
> --- a/libavcodec/v4l2_buffers.c
> +++ b/libavcodec/v4l2_buffers.c
> @@ -356,6 +356,33 @@ static int v4l2_buffer_buf_to_swframe(AVFrame *frame, V4L2Buffer *avbuf)
> return 0;
> }
>
> +static int v4l2_plane_to_plane_align(V4L2Buffer *out, int plane, const uint8_t* data, int size, int offset, int width, int height, int stride)
> +{
> + unsigned int bytesused, length;
> +
> + if (plane >= out->num_planes)
> + return AVERROR(EINVAL);
> +
> + length = out->plane_info[plane].length;
> + bytesused = FFMIN(size+offset, length);
> +
> + for (int i = 0; i < height; i++) {
> + memcpy((uint8_t*)out->plane_info[plane].mm_addr + offset, data, width);
> + offset += stride;
> + data += width;
> + }
> +
> + if (V4L2_TYPE_IS_MULTIPLANAR(out->buf.type)) {
> + out->planes[plane].bytesused = bytesused;
> + out->planes[plane].length = length;
> + } else {
> + out->buf.bytesused = bytesused;
> + out->buf.length = length;
> + }
> +
> + return 0;
> +}
> +
> static int v4l2_buffer_swframe_to_buf(const AVFrame *frame, V4L2Buffer *out)
> {
> int i, ret;
> @@ -364,7 +391,11 @@ static int v4l2_buffer_swframe_to_buf(const AVFrame *frame, V4L2Buffer *out)
> fmt.fmt.pix_mp.pixelformat : fmt.fmt.pix.pixelformat;
> int height = V4L2_TYPE_IS_MULTIPLANAR(fmt.type) ?
> fmt.fmt.pix_mp.height : fmt.fmt.pix.height;
> - int is_planar_format = 0;
> + int bytesperline = V4L2_TYPE_IS_MULTIPLANAR(fmt.type) ?
> + (fmt.fmt.pix_mp.num_planes ? fmt.fmt.pix_mp.plane_fmt[0].bytesperline: 0) : fmt.fmt.pix.bytesperline;
The doc says bytesperline can be zero
__u32 bytesperline; /* for padding, zero if unused */
> + int sizeimage = V4L2_TYPE_IS_MULTIPLANAR(fmt.type) ?
> + (fmt.fmt.pix_mp.num_planes ? fmt.fmt.pix_mp.plane_fmt[0].sizeimage: 0) : fmt.fmt.pix.sizeimage;
> + int is_planar_format = 0, scanline_y = 0, scanline_uv = 0;
>
> switch (pixel_format) {
> case V4L2_PIX_FMT_YUV420M:
> @@ -398,16 +429,41 @@ static int v4l2_buffer_swframe_to_buf(const AVFrame *frame, V4L2Buffer *out)
> for (i = 0; i < desc->nb_components; i++)
> planes_nb = FFMAX(planes_nb, desc->comp[i].plane + 1);
>
> + switch (pixel_format)
> + {
> + /* Currently only NV12 & NV21 are addressed for buffer alignment issue */
> + case V4L2_PIX_FMT_NV12:
> + case V4L2_PIX_FMT_NV21:
> + scanline_y = sizeimage / bytesperline * 2 / 3;
> + scanline_uv = scanline_y / 2;
> + break;
> + default:
> + /* By default, no buffer alignment issues are expected */
> + scanline_y = height;
> + scanline_uv = AV_CEIL_RSHIFT(height, desc->log2_chroma_h);
> + bytesperline = frame->linesize[0];
> + break;
> + }
I think you can use the information in const AVPixFmtDescriptor *desc to handle
all formats than switch case for each one.
Please send a PR to https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls
> +
> for (i = 0; i < planes_nb; i++) {
> int size, h = height;
> if (i == 1 || i == 2) {
> h = AV_CEIL_RSHIFT(h, desc->log2_chroma_h);
> }
> - size = frame->linesize[i] * h;
> - ret = v4l2_bufref_to_buf(out, 0, frame->data[i], size, offset);
> - if (ret)
> - return ret;
> - offset += size;
> +
> + if (bytesperline == frame->linesize[0]) {
> + size = frame->linesize[i] * h;
> + ret = v4l2_bufref_to_buf(out, 0, frame->data[i], size, offset);
> + if (ret)
> + return ret;
> + offset += frame->linesize[i] * (i ? scanline_uv : scanline_y);
> + } else {
> + size = bytesperline * (i ? scanline_uv : scanline_y);
> + ret = v4l2_plane_to_plane_align(out, 0, frame->data[i], size, offset, frame->linesize[i], h, bytesperline);
> + if (ret)
> + return ret;
> + offset += size;
> + }
> }
> return 0;
> }
> --
> 2.34.1
>
> _______________________________________________
> ffmpeg-devel mailing list -- ffmpeg-devel@ffmpeg.org
> To unsubscribe send an email to ffmpeg-devel-leave@ffmpeg.org
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2025-11-13 3:29 [FFmpeg-devel] [PATCH] libavcodec/v4l2_buffers: fixing buffer alignment issue Wenjie Yin via ffmpeg-devel
2025-11-13 6:56 ` [FFmpeg-devel] " Zhao Zhili via ffmpeg-devel
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