[FFmpeg-devel] [PATCH] lavf/rtpenc_jpeg: Retrieve sampling factor from SOF0

[Yeoh, Hoong Tee]

In ff_rtp_send_jpeg, the type is defined based on PIX_FMT and color-range parsed in.
There is limitation on current design where need to include support newly introduced
PIX_FMT such as AV_PIX_FMT_QSV and there might be more and more in future.
Hence, retrive the sampling factor from SOF0 in JPEG compressed header directly.
This introduces flexibility to handle the current limitation.

Signed-off-by: Yeoh, Hoong Tee <hoong.tee.yeoh at intel.com>
---
 libavformat/rtpenc_jpeg.c | 41 +++++++++++++++++++++++++--------------
 1 file changed, 26 insertions(+), 15 deletions(-)

diff --git a/libavformat/rtpenc_jpeg.c b/libavformat/rtpenc_jpeg.c
index 9111683..53be188 100644
--- a/libavformat/rtpenc_jpeg.c
+++ b/libavformat/rtpenc_jpeg.c
@@ -30,7 +30,7 @@ void ff_rtp_send_jpeg(AVFormatContext *s1, const uint8_t *buf, int size)
     RTPMuxContext *s = s1->priv_data;
     const uint8_t *qtables[4] = { NULL };
     int nb_qtables = 0;
-    uint8_t type;
+    uint8_t type = 2; /* initialized non-0/1 value for RTP/JPEG type check*/
     uint8_t w, h;
     uint8_t *p;
     int off = 0; /* fragment offset of the current JPEG frame */
@@ -45,20 +45,6 @@ void ff_rtp_send_jpeg(AVFormatContext *s1, const uint8_t *buf, int size)
     w = AV_CEIL_RSHIFT(s1->streams[0]->codecpar->width, 3);
     h = AV_CEIL_RSHIFT(s1->streams[0]->codecpar->height, 3);
 
-    /* get the pixel format type or fail */
-    if (s1->streams[0]->codecpar->format == AV_PIX_FMT_YUVJ422P ||
-        (s1->streams[0]->codecpar->color_range == AVCOL_RANGE_JPEG &&
-         s1->streams[0]->codecpar->format == AV_PIX_FMT_YUV422P)) {
-        type = 0;
-    } else if (s1->streams[0]->codecpar->format == AV_PIX_FMT_YUVJ420P ||
-               (s1->streams[0]->codecpar->color_range == AVCOL_RANGE_JPEG &&
-                s1->streams[0]->codecpar->format == AV_PIX_FMT_YUV420P)) {
-        type = 1;
-    } else {
-        av_log(s1, AV_LOG_ERROR, "Unsupported pixel format\n");
-        return;
-    }
-
     /* preparse the header for getting some info */
     for (i = 0; i < size; i++) {
         if (buf[i] != 0xff)
@@ -90,6 +76,23 @@ void ff_rtp_send_jpeg(AVFormatContext *s1, const uint8_t *buf, int size)
                        "Only 1x1 chroma blocks are supported. Aborted!\n");
                 return;
             }
+
+	    /*
+	     * Find out the sampling factor in SOF0.
+	     * In SOF0, hsample/vsample is inserted in form of (2<<4) | (type ? 2 : 1).
+	     * First 4-bit is hsample while Last 4-bit is vsample.
+	     */
+
+            /* Luma channel sampling factor in 4:2:2 chroma subsampling are 2x1 */
+            if (buf[i + 11] == 33) {
+                type = 0;
+            /* Luma channel sampling factor in 4:2:0 chroma subsampling are 2x2 */
+            } else if (buf[i + 11] == 34) {
+                type = 1;
+            } else {
+                av_log(s1, AV_LOG_ERROR, "Unsupported pixel format\n");
+                return;
+            }
         } else if (buf[i + 1] == DHT) {
             int dht_size = AV_RB16(&buf[i + 2]);
             default_huffman_tables |= 1 << 4;
@@ -163,6 +166,14 @@ void ff_rtp_send_jpeg(AVFormatContext *s1, const uint8_t *buf, int size)
             break;
         }
     }
+
+    /* Check validity of RTP/JPEG type */
+    if (type != 0 && type != 1) {
+        av_log(s1, AV_LOG_ERROR,
+                "Invalid RTP/JPEG type\n");
+        return;
+    }
+
     if (default_huffman_tables && default_huffman_tables != 31) {
         av_log(s1, AV_LOG_ERROR,
                "RFC 2435 requires standard Huffman tables for jpeg\n");
-- 
2.34.1