[PATCH v4l-utils 0/2] v4l2-tracer: fix expected frame length calculation

[PATCH v4l-utils 0/2] v4l2-tracer: fix expected frame length calculation

[Sarah Gershuni]

This series fixes the calculation of expected frame lengths in v4l2-tracer. 
Previously, the calculation assumed that the stride equals the width and that chroma 
padding follows the end of the plane, which could result in incorrect lengths.

Patch 1/2: add plane_bytesperline to trace_context
- Introduces `plane_bytesperline` to store the stride of each plane, providing the 
  necessary data to compute accurate frame lengths.

Patch 2/2: calculate expected length using v4l2-fwht info
- Computes the frame length per plane correctly, fixing previous inaccuracies.

Together, these patches ensure that v4l2-tracer calculates expected frame lengths 
accurately for all supported pixel formats.

Signed-off-by: Sarah Gershuni <sarah556726@gmail.com>


Sarah Gershuni (2):
  add plane_bytesperline to trace_context
  calculate expected length using v4l2-fwht info

 utils/v4l2-tracer/trace-helper.cpp | 55 ++++++++++++++++++++++--------
 utils/v4l2-tracer/trace.h          |  1 +
 2 files changed, 42 insertions(+), 14 deletions(-)

-- 
2.43.0

[PATCH v4l-utils 1/2] add plane_bytesperline to trace_context

[Sarah Gershuni]

Add plane_bytesperline array to trace_context to store stride per plane for
multiplanar formats. Update g_fmt_setup_trace to initialize the array.

Signed-off-by: Sarah Gershuni <sarah556726@gmail.com>
---
 utils/v4l2-tracer/trace-helper.cpp | 15 +++++++++++++--
 utils/v4l2-tracer/trace.h          |  1 +
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/utils/v4l2-tracer/trace-helper.cpp b/utils/v4l2-tracer/trace-helper.cpp
index 9e5747a2..6c296dbf 100644
--- a/utils/v4l2-tracer/trace-helper.cpp
+++ b/utils/v4l2-tracer/trace-helper.cpp
@@ -399,16 +399,27 @@ void g_fmt_setup_trace(struct v4l2_format *format)
 		ctx_trace.width = format->fmt.pix.width;
 		ctx_trace.height = format->fmt.pix.height;
 		ctx_trace.pixelformat = format->fmt.pix.pixelformat;
+		ctx_trace.plane_bytesperline[0] = format->fmt.pix.bytesperline;
 	}
 	if (format->type == V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE) {
 		ctx_trace.width = format->fmt.pix_mp.width;
 		ctx_trace.height = format->fmt.pix_mp.height;
 		ctx_trace.pixelformat = format->fmt.pix_mp.pixelformat;
+
+		for (unsigned i = 0; i < format->fmt.pix_mp.num_planes; i++){
+			ctx_trace.plane_bytesperline[i] = format->fmt.pix_mp.plane_fmt[i].bytesperline;
+		}
 	}
-	if (format->type == V4L2_BUF_TYPE_VIDEO_OUTPUT)
+	if (format->type == V4L2_BUF_TYPE_VIDEO_OUTPUT){
 		ctx_trace.compression_format = format->fmt.pix.pixelformat;
-	if (format->type == V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE)
+		ctx_trace.plane_bytesperline[0] = format->fmt.pix.bytesperline;
+	}
+	if (format->type == V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE){
 		ctx_trace.compression_format = format->fmt.pix_mp.pixelformat;
+		for (unsigned i = 0; i < format->fmt.pix_mp.num_planes; i++){
+			ctx_trace.plane_bytesperline[i] = format->fmt.pix_mp.plane_fmt[i].bytesperline;
+		}
+	}
 }
 
 void s_fmt_setup(struct v4l2_format *format)
diff --git a/utils/v4l2-tracer/trace.h b/utils/v4l2-tracer/trace.h
index a74a5f3f..7f166287 100644
--- a/utils/v4l2-tracer/trace.h
+++ b/utils/v4l2-tracer/trace.h
@@ -32,6 +32,7 @@ struct trace_context {
 	__u32 pixelformat;
 	std::string media_device;
 	__u32 compression_format;
+	__u32 plane_bytesperline[VIDEO_MAX_PLANES];
 	union {
 		struct h264_info h264;
 	} fmt;
-- 
2.43.0

[PATCH v4l-utils 2/2] calculate expected length using v4l2-fwht info

[Sarah Gershuni]

Update get_expected_length_trace to calculate the expected buffer length
based on v4l2_fwht_find_pixfmt info.

Signed-off-by: Sarah Gershuni <sarah556726@gmail.com>
---
 utils/v4l2-tracer/trace-helper.cpp | 40 +++++++++++++++++++++---------
 1 file changed, 28 insertions(+), 12 deletions(-)

diff --git a/utils/v4l2-tracer/trace-helper.cpp b/utils/v4l2-tracer/trace-helper.cpp
index 6c296dbf..a59d7761 100644
--- a/utils/v4l2-tracer/trace-helper.cpp
+++ b/utils/v4l2-tracer/trace-helper.cpp
@@ -6,6 +6,11 @@
 #include "trace.h"
 #include <math.h>
 
+extern "C" {
+#include "codec-v4l2-fwht.h"
+}
+
+
 struct trace_context ctx_trace = {};
 
 bool is_video_or_media_device(const char *path)
@@ -233,18 +238,29 @@ void print_buffers_trace(void)
 
 unsigned get_expected_length_trace()
 {
-	/*
-	 * TODO: this assumes that the stride is equal to the real width and that the
-	 * padding follows the end of the chroma plane. It could be improved by
-	 * following the model in v4l2-ctl-streaming.cpp read_write_padded_frame()
-	 */
-	unsigned expected_length = ctx_trace.width * ctx_trace.height;
-	if (ctx_trace.pixelformat == V4L2_PIX_FMT_NV12 || ctx_trace.pixelformat == V4L2_PIX_FMT_YUV420) {
-		expected_length *= 3;
-		expected_length /= 2;
-		expected_length += (expected_length % 2);
-	}
-	return expected_length;
+	const auto *info = v4l2_fwht_find_pixfmt(ctx_trace.pixelformat);
+    if (!info)
+		return 0;
+
+    unsigned coded_height = ctx_trace.height;
+    unsigned expected = 0;
+
+    for (unsigned plane_idx = 0; plane_idx < info->planes_num; ++plane_idx) {
+        unsigned stride = ctx_trace.plane_bytesperline[plane_idx];
+        
+        bool is_chroma = (plane_idx == 1 || plane_idx == 2);
+        unsigned h_div = is_chroma ? info->height_div : 1;
+
+        if (info->planes_num == 3 && plane_idx == 1)
+            stride /= 2;
+
+        if (plane_idx == 1 &&
+            (info->id == V4L2_PIX_FMT_NV24 || info->id == V4L2_PIX_FMT_NV42))
+            stride *= 2;
+
+        expected += stride * (coded_height / h_div);
+    }
+    return expected;
 }
 
 void s_ext_ctrls_setup(struct v4l2_ext_controls *ext_controls)
-- 
2.43.0

Re: [PATCH v4l-utils 2/2] calculate expected length using v4l2-fwht info

[Hans Verkuil]

Hi Sarah,

On 16/03/2026 14:22, Sarah Gershuni wrote:
> Update get_expected_length_trace to calculate the expected buffer length
> based on v4l2_fwht_find_pixfmt info.
> 
> Signed-off-by: Sarah Gershuni <sarah556726@gmail.com>
> ---
>  utils/v4l2-tracer/trace-helper.cpp | 40 +++++++++++++++++++++---------
>  1 file changed, 28 insertions(+), 12 deletions(-)
> 
> diff --git a/utils/v4l2-tracer/trace-helper.cpp b/utils/v4l2-tracer/trace-helper.cpp
> index 6c296dbf..a59d7761 100644
> --- a/utils/v4l2-tracer/trace-helper.cpp
> +++ b/utils/v4l2-tracer/trace-helper.cpp
> @@ -6,6 +6,11 @@
>  #include "trace.h"
>  #include <math.h>
>  
> +extern "C" {
> +#include "codec-v4l2-fwht.h"
> +}
> +
> +
>  struct trace_context ctx_trace = {};
>  
>  bool is_video_or_media_device(const char *path)
> @@ -233,18 +238,29 @@ void print_buffers_trace(void)
>  
>  unsigned get_expected_length_trace()
>  {
> -	/*
> -	 * TODO: this assumes that the stride is equal to the real width and that the
> -	 * padding follows the end of the chroma plane. It could be improved by
> -	 * following the model in v4l2-ctl-streaming.cpp read_write_padded_frame()
> -	 */
> -	unsigned expected_length = ctx_trace.width * ctx_trace.height;
> -	if (ctx_trace.pixelformat == V4L2_PIX_FMT_NV12 || ctx_trace.pixelformat == V4L2_PIX_FMT_YUV420) {
> -		expected_length *= 3;
> -		expected_length /= 2;
> -		expected_length += (expected_length % 2);
> -	}
> -	return expected_length;
> +	const auto *info = v4l2_fwht_find_pixfmt(ctx_trace.pixelformat);
> +    if (!info)
> +		return 0;
> +
> +    unsigned coded_height = ctx_trace.height;
> +    unsigned expected = 0;
> +
> +    for (unsigned plane_idx = 0; plane_idx < info->planes_num; ++plane_idx) {
> +        unsigned stride = ctx_trace.plane_bytesperline[plane_idx];

Ah, this does not work. All the pixelformats that v4l2_fwht_find_pixfmt knows are
all single buffer formats, i.e. all planes are combined in a single buffer.
So there is also just one bytesperline value.

I know, it's very confusing: the _MPLANE buffer types should really be called
_MBUFFER in hindsight. I.e. each plane has its own buffer as opposed to
concatenating all planes in a single buffer.

I'm not sure what problem you are attempting to fix, but I don't think this does
what you want it to do.

Although patch 1/2 looks fine, I'll drop both patches since it makes no sense
in combination with this patch.

It really only makes sense for multiplanar pixelformats like V4L2_PIX_FMT_NV12M,
V4L2_PIX_FMT_YUV420M, etc., but that's not what this second patch deals with.

Regards,

	Hans

> +        
> +        bool is_chroma = (plane_idx == 1 || plane_idx == 2);
> +        unsigned h_div = is_chroma ? info->height_div : 1;
> +
> +        if (info->planes_num == 3 && plane_idx == 1)
> +            stride /= 2;
> +
> +        if (plane_idx == 1 &&
> +            (info->id == V4L2_PIX_FMT_NV24 || info->id == V4L2_PIX_FMT_NV42))
> +            stride *= 2;
> +
> +        expected += stride * (coded_height / h_div);
> +    }
> +    return expected;
>  }
>  
>  void s_ext_ctrls_setup(struct v4l2_ext_controls *ext_controls)