lavc/encode: make sure frame timebase matches encoder, when set

AVFrame.time_base has been added recently, but is currently not used for
anything. Prepare for its use in encoders by rejecting frames where
time_base is set, but differs from the AVCodecContext one.

3 files changed, 15 insertions, 2 deletions

diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index 65c8535359..9c246c455c 100644
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -2645,6 +2645,10 @@ int avcodec_receive_frame(AVCodecContext *avctx, AVFrame *frame);
  *                  packets are ignored, and sending frames will return
  *                  AVERROR_EOF.
  *
+ *                  frame->time_base should be set to the same value as
+ *                  avctx->time_base. This is not required yet, but may be in
+ *                  the future.
+ *
  *                  For audio:
  *                  If AV_CODEC_CAP_VARIABLE_FRAME_SIZE is set, then each frame
  *                  can have any number of samples.
diff --git a/libavcodec/encode.c b/libavcodec/encode.c
index bd66f138a3..a774dc28dc 100644
--- a/libavcodec/encode.c
+++ b/libavcodec/encode.c
@@ -361,6 +361,14 @@ static int encode_send_frame_internal(AVCodecContext *avctx, const AVFrame *src)
     AVFrame *dst = avci->buffer_frame;
     int ret;
 
+    /* make sure the frame's timebase (if set) matches the encoder one */
+    if (src->time_base.num &&
+        (src->time_base.num != avctx->time_base.num ||
+         src->time_base.den != avctx->time_base.den)) {
+        av_log(avctx, AV_LOG_ERROR, "Mismatching frame/encoder time base\n");
+        return AVERROR(EINVAL);
+    }
+
     if (avctx->codec->type == AVMEDIA_TYPE_AUDIO) {
         /* extract audio service type metadata */
         AVFrameSideData *sd = av_frame_get_side_data(src, AV_FRAME_DATA_AUDIO_SERVICE_TYPE);
diff --git a/libavutil/frame.h b/libavutil/frame.h
index 6d9563bc5d..c5e2de85b3 100644
--- a/libavutil/frame.h
+++ b/libavutil/frame.h
@@ -441,8 +441,9 @@ typedef struct AVFrame {
     /**
      * Time base for the timestamps in this frame.
      * In the future, this field may be set on frames output by decoders or
-     * filters, but its value will be by default ignored on input to encoders
-     * or filters.
+     * filters; its value will be by default ignored on input to filters.
+     * For frames sent to encoders, it should be set by the user to the same
+     * value as AVCodecContext.time_base.
      */
     AVRational time_base;