vqa: set time base to frame rate as coded in the header.

According to Multimedia Wiki documentation, the frame rate is not always 15,
and the actual value can be found in the header.

libavformat/westwood_vqa.c

@@ -51,7 +51,6 @@
 #define CMDS_TAG MKBETAG('C', 'M', 'D', 'S')
 
 #define VQA_HEADER_SIZE 0x2A
-#define VQA_FRAMERATE 15
 #define VQA_PREAMBLE_SIZE 8
 
 typedef struct WsVqaDemuxContext {
@@ -87,13 +86,13 @@ static int wsvqa_read_header(AVFormatContext *s,
     unsigned char scratch[VQA_PREAMBLE_SIZE];
     unsigned int chunk_tag;
     unsigned int chunk_size;
+    int fps;
 
     /* initialize the video decoder stream */
     st = avformat_new_stream(s, NULL);
     if (!st)
         return AVERROR(ENOMEM);
     st->start_time = 0;
-    avpriv_set_pts_info(st, 33, 1, VQA_FRAMERATE);
     wsvqa->video_stream_index = st->index;
     st->codec->codec_type = AVMEDIA_TYPE_VIDEO;
     st->codec->codec_id = CODEC_ID_WS_VQA;
@@ -113,6 +112,12 @@ static int wsvqa_read_header(AVFormatContext *s,
     }
     st->codec->width = AV_RL16(&header[6]);
     st->codec->height = AV_RL16(&header[8]);
+    fps = header[12];
+    if (fps < 1 || fps > 30) {
+        av_log(s, AV_LOG_ERROR, "invalid fps: %d\n", fps);
+        return AVERROR_INVALIDDATA;
+    }
+    avpriv_set_pts_info(st, 64, 1, fps);
 
     /* initialize the audio decoder stream for VQA v1 or nonzero samplerate */
     if (AV_RL16(&header[24]) || (AV_RL16(&header[0]) == 1 && AV_RL16(&header[2]) == 1)) {