Try harder with small clips with sparse keyframes

Fixes #41
Marginal · Jun 13, 2017 · 218030a · 218030a
1 parent 4ff57c1
commit 218030a
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Showing 3 changed files with 12 additions and 7 deletions.
diff --git a/qlgenerator/GeneratePreviewForURL.m b/qlgenerator/GeneratePreviewForURL.m
@@ -242,9 +242,9 @@ OSStatus GeneratePreviewForURL(void *thisInterface, QLPreviewRequestRef preview,
                 NSInteger snapshot_time = [defaults integerForKey:kSettingsSnapshotTime];
                 if (snapshot_time <= 0)
                     snapshot_time = kDefaultSnapshotTime;
-                NSInteger time = duration < kMinimumDuration ? 0 : (duration < 2 * snapshot_time ? duration/2 : snapshot_time);
+                NSInteger time = duration < kMinimumDuration ? -1 : (duration < 2 * snapshot_time ? duration/2 : snapshot_time);
                 thePreview = [snapshotter newSnapshotWithSize:size atTime:time];
-                if (!thePreview && time)
+                if (!thePreview && time > 0)
                     thePreview = [snapshotter newSnapshotWithSize:size atTime:0];    // Failed. Try again at start.
             }
         }   // Free snapshotter and ffmpeg resources before handing back to QuickLook

diff --git a/qlgenerator/GenerateThumbnailForURL.m b/qlgenerator/GenerateThumbnailForURL.m
@@ -79,9 +79,9 @@ OSStatus GenerateThumbnailForURL(void *thisInterface, QLThumbnailRequestRef thum
             snapshot_time = kDefaultSnapshotTime;
 
         NSInteger duration = [snapshotter duration];
-        NSInteger time = duration < kMinimumDuration ? 0 : (duration < 2 * snapshot_time ? duration/2 : snapshot_time);
+        NSInteger time = duration < kMinimumDuration ? -1 : (duration < 2 * snapshot_time ? duration/2 : snapshot_time);
         snapshot = [snapshotter newSnapshotWithSize:scaled atTime:time];
-        if (!snapshot && time)
+        if (!snapshot && time > 0)
             snapshot = [snapshotter newSnapshotWithSize:size atTime:0];    // Failed. Try again at start.
     }   // Free snapshotter and ffmpeg resources before handing back to QuickLook
 

diff --git a/qlgenerator/Snapshotter.m b/qlgenerator/Snapshotter.m
@@ -192,13 +192,15 @@ - (int) newImageWithSize:(CGSize)size atTime:(NSInteger)seconds to:(uint8_t *con
     int64_t stoptime;
     if (seconds > 0)
     {
+        avcodec_flush_buffers(dec_ctx);    // Discard any buffered packets left over from previous call
         timestamp += av_rescale(seconds, stream->time_base.den, stream->time_base.num);
         stoptime = timestamp + av_rescale(kMaxKeyframeTime, stream->time_base.den, stream->time_base.num);
         if (av_seek_frame(fmt_ctx, stream_idx, timestamp, AVSEEK_FLAG_BACKWARD) < 0)    // AVSEEK_FLAG_BACKWARD is more reliable for MP4 container
             return -1;
     }
     else if (seconds == 0 && !(fmt_ctx->iformat->flags & AVFMT_NO_BYTE_SEEK))  // rewind
     {
+        avcodec_flush_buffers(dec_ctx);    // Discard any buffered packets left over from previous call
         av_seek_frame(fmt_ctx, stream_idx, 0, AVSEEK_FLAG_BYTE);
         stoptime = av_rescale(kMaxKeyframeTime, stream->time_base.den, stream->time_base.num);
     }
@@ -217,15 +219,18 @@ - (int) newImageWithSize:(CGSize)size atTime:(NSInteger)seconds to:(uint8_t *con
         return -1;
 
     int got_frame = 0;
-    avcodec_flush_buffers(dec_ctx);    // Discard any buffered packets left over from previous call
     while (av_read_frame(fmt_ctx, &pkt) >= 0 && !got_frame)
     {
         if (pkt.stream_index == stream_idx)
         {
             avcodec_decode_video2(dec_ctx, frame, &got_frame, &pkt);
 
-            // MPEG TS demuxer doesn't necessarily seek to keyframes. So keep looking for one.
-            if (got_frame && !frame->key_frame && frame->pkt_pts < stoptime)
+            if (got_frame && seconds > 0 &&
+                (
+                 // It's a small clip and we've ended up at a keyframe at start of it. Keep reading until desired time.
+                 (seconds <= kMaxKeyframeTime && frame->pts < timestamp) ||
+                 // MPEG TS demuxer doesn't necessarily seek to keyframes. So keep looking for one.
+                 ((seconds > kMaxKeyframeTime && !frame->key_frame && frame->pts < stoptime))))
             {
                 got_frame = 0;
                 av_frame_unref(frame);