[FFmpeg-devel] [RFC PATCH] lavd/v4l2: cover all bufer if bytesperline is set by driver

[Dima Buzdyk]

Some drivers may set bytesperline if hardware use padding bytes for
alignment. In this case lavd/v4l2 will expect W*H bytes per frame, but
driver will provide Pitch*H bytes which makes v4l2 unhappy.

This change adjusts frame width to cover entire data buffer aligning
lavd/v4l2 expectations with data provided by the driver. As a result
user will be able to get image stream from device, albeit having
garbage in padding bytes.

Signed-off-by: Dima Buzdyk <dima.buzdyk at gmail.com>
---
 libavdevice/v4l2.c | 32 +++++++++++++++++++++++++++-----
 1 file changed, 27 insertions(+), 5 deletions(-)

diff --git a/libavdevice/v4l2.c b/libavdevice/v4l2.c
index 5e85d1a2b3..b1e837f740 100644
--- a/libavdevice/v4l2.c
+++ b/libavdevice/v4l2.c
@@ -83,7 +83,7 @@ struct video_data {
     AVClass *class;
     int fd;
     int pixelformat; /* V4L2_PIX_FMT_* */
-    int width, height;
+    int width, height, pitch;
     int frame_size;
     int interlaced;
     int top_field_first;
@@ -202,7 +202,7 @@ fail:
 }
 
 static int device_init(AVFormatContext *ctx, int *width, int *height,
-                       uint32_t pixelformat)
+                       int *pitch, uint32_t pixelformat)
 {
     struct video_data *s = ctx->priv_data;
     struct v4l2_format fmt = { .type = V4L2_BUF_TYPE_VIDEO_CAPTURE };
@@ -224,6 +224,7 @@ static int device_init(AVFormatContext *ctx, int *width, int *height,
                *width, *height, fmt.fmt.pix.width, fmt.fmt.pix.height);
         *width = fmt.fmt.pix.width;
         *height = fmt.fmt.pix.height;
+        *pitch = fmt.fmt.pix.bytesperline;
     }
 
     if (pixelformat != fmt.fmt.pix.pixelformat) {
@@ -779,6 +780,7 @@ static int device_try_init(AVFormatContext *ctx,
                            enum AVPixelFormat pix_fmt,
                            int *width,
                            int *height,
+                           int *pitch,
                            uint32_t *desired_format,
                            enum AVCodecID *codec_id)
 {
@@ -787,7 +789,7 @@ static int device_try_init(AVFormatContext *ctx,
     *desired_format = ff_fmt_ff2v4l(pix_fmt, ctx->video_codec_id);
 
     if (*desired_format) {
-        ret = device_init(ctx, width, height, *desired_format);
+        ret = device_init(ctx, width, height, pitch, *desired_format);
         if (ret < 0) {
             *desired_format = 0;
             if (ret != AVERROR(EINVAL))
@@ -804,7 +806,7 @@ static int device_try_init(AVFormatContext *ctx,
                        (char *)av_x_if_null(av_get_pix_fmt_name(ff_fmt_conversion_table[i].ff_fmt), "none"));
 
                 *desired_format = ff_fmt_conversion_table[i].v4l2_fmt;
-                ret = device_init(ctx, width, height, *desired_format);
+                ret = device_init(ctx, width, height, pitch, *desired_format);
                 if (ret >= 0)
                     break;
                 else if (ret != AVERROR(EINVAL))
@@ -933,11 +935,13 @@ static int v4l2_read_header(AVFormatContext *ctx)
 
         s->width  = fmt.fmt.pix.width;
         s->height = fmt.fmt.pix.height;
+        s->pitch  = fmt.fmt.pix.bytesperline;
         av_log(ctx, AV_LOG_VERBOSE,
                "Setting frame size to %dx%d\n", s->width, s->height);
     }
 
-    res = device_try_init(ctx, pix_fmt, &s->width, &s->height, &desired_format, &codec_id);
+    res = device_try_init(ctx, pix_fmt, &s->width, &s->height, &s->pitch,
+                          &desired_format, &codec_id);
     if (res < 0)
         goto fail;
 
@@ -948,6 +952,24 @@ static int v4l2_read_header(AVFormatContext *ctx)
     if (codec_id != AV_CODEC_ID_NONE && ctx->video_codec_id == AV_CODEC_ID_NONE)
         ctx->video_codec_id = codec_id;
 
+    /* If bytesperpixel is set by driver then set width co cover full
+     * buffer area even if there are garbage data to be displayed.
+     * It is better to display padding bytes and give application ability
+     * to crop image later than fail to display image stream completely */
+    if (s->pitch) {
+        int linesize;
+
+        pix_fmt = ff_fmt_v4l2ff(desired_format, codec_id);
+        linesize = av_image_get_linesize(pix_fmt, s->width, 0);
+        if (linesize > 0) {
+            s->width = s->pitch * s->width / linesize;
+
+            av_log(ctx, AV_LOG_INFO,
+                   "Expand frame width to %dx%d to cover full buffer\n",
+                   s->width, s->height);
+        }
+    }
+
     if ((res = av_image_check_size(s->width, s->height, 0, ctx)) < 0)
         goto fail;
 
-- 
2.37.2