[FFmpeg-devel] Re: [PATCH] libavcodec/v4l2_buffers: fixing buffer alignment issue

[Wenjie Yin via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

Hi Team,

I hope this message finds you well. I wanted to drop a gentle reminder regarding the patch I submitted recently. When you have a moment, could you please review it? Your feedback is invaluable, and I look forward to any insights or suggestions you might have.

Thank you so much for your time and assistance!

Best regards,
Wenjie Yin

-----Original Message-----
From: Wenjie.Yin On Behalf Of Wenjie Yin
Sent: Wednesday, October 29, 2025 5:20 PM
To: 'ffmpeg-devel@ffmpeg.org' <ffmpeg-devel@ffmpeg.org>; Wenjie Yin <wenjyin@qti.qualcomm.com>
Cc: 'wangao.wang@oss.qualcomm.com' <wangao.wang@oss.qualcomm.com>; Qiwei Liu (QUIC) <quic_qiweil@quicinc.com>; 'renjiang.han@oss.qualcomm.com' <renjiang.han@oss.qualcomm.com>
Subject: [PATCH] libavcodec/v4l2_buffers: fixing buffer alignment issue

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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