avformat/img2enc: add frame_pts option for make output filename

fix ticket id: #1452
when use frame_pts option, the output image name can be set with PTS
of current frame.
Signed-off-by: Steven Liu <lq@onvideo.cn>

doc/muxers.texi

@@ -897,9 +897,18 @@ can be used:
 ffmpeg -f v4l2 -r 1 -i /dev/video0 -f image2 -strftime 1 "%Y-%m-%d_%H-%M-%S.jpg"
 @end example
 
+You can set the file name with current frame's PTS:
+@example
+ffmpeg -f v4l2 -r 1 -i /dev/video0 -copyts -f image2 -frame_pts true %d.jpg"
+@end example
+
 @subsection Options
 
 @table @option
+@item frame_pts
+If set to 1, expand the filename with pts from pkt->pts.
+Default value is 0.
+
 @item start_number
 Start the sequence from the specified number. Default value is 1.
 

libavformat/img2enc.c

@@ -42,6 +42,7 @@ typedef struct VideoMuxData {
     char target[4][1024];
     int update;
     int use_strftime;
+    int frame_pts;
     const char *muxer;
     int use_rename;
 } VideoMuxData;
@@ -99,6 +100,11 @@ static int write_packet(AVFormatContext *s, AVPacket *pkt)
                 av_log(s, AV_LOG_ERROR, "Could not get frame filename with strftime\n");
                 return AVERROR(EINVAL);
             }
+        } else if (img->frame_pts) {
+            if (av_get_frame_filename2(filename, sizeof(filename), img->path, pkt->pts, AV_FRAME_FILENAME_FLAGS_MULTIPLE) < 0) {
+                av_log(s, AV_LOG_ERROR, "Cannot write filename by pts of the frames.");
+                return AVERROR(EINVAL);
+            }
         } else if (av_get_frame_filename2(filename, sizeof(filename), img->path,
                                           img->img_number,
                                           AV_FRAME_FILENAME_FLAGS_MULTIPLE) < 0 &&
@@ -206,6 +212,7 @@ static const AVOption muxoptions[] = {
     { "update",       "continuously overwrite one file", OFFSET(update),  AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0,       1, ENC },
     { "start_number", "set first number in the sequence", OFFSET(img_number), AV_OPT_TYPE_INT,  { .i64 = 1 }, 0, INT_MAX, ENC },
     { "strftime",     "use strftime for filename", OFFSET(use_strftime),  AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, ENC },
+    { "frame_pts",    "use current frame pts for filename", OFFSET(frame_pts),  AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, ENC },
     { "atomic_writing", "write files atomically (using temporary files and renames)", OFFSET(use_rename), AV_OPT_TYPE_BOOL, { .i64 = 0 }, 0, 1, ENC },
     { NULL },
 };