We've been in this fuzzy situation where maybe you could call
avcodec_flush_buffers() on an encoder but there weren't any encoders
that supported it except maybe audiotoolboxenc. Then we added flush
support to nvenc very intentionally, and it worked, but that was more a
coincidence than anything else. And if you call avcodec_flush_buffers()
on an encoder that doesn't support it, it'll leave the encoder in an
undefined state, so that's not great.
As part of cleaning this up, this change introduces a formal capability
flag for encoders that support flushing and ensures a flush call is a
no-op for any other encoder. This allows client code to check if it is
meaningful to call flush on an encoder before actually doing it.
I have not attempted to separate the steps taken inside
avcodec_flush_buffers() because it's not doing anything that's wrong
for an encoder. But I did add a sanity check to reject attempts to
flush a frame threaded encoder because I couldn't wrap my head around
whether that code path was actually safe or not. As this combination
doesn't exist today, we'll deal with it if it ever comes up.
Signed-off-by: Philip Langdale <phil...@overt.org>
---
libavcodec/audiotoolboxenc.c | 3 ++-
libavcodec/avcodec.h | 21 ++++++++++++++++-----
libavcodec/decode.c | 18 ++++++++++++++++++
libavcodec/nvenc_hevc.c | 6 ++++--
4 files changed, 40 insertions(+), 8 deletions(-)
diff --git a/libavcodec/audiotoolboxenc.c b/libavcodec/audiotoolboxenc.c
index 2c1891693e..7cb5ffd915 100644
--- a/libavcodec/audiotoolboxenc.c
+++ b/libavcodec/audiotoolboxenc.c
@@ -627,7 +627,8 @@ static const AVOption options[] = {
.encode2 = ffat_encode, \
.flush = ffat_encode_flush, \
.priv_class = &ffat_##NAME##_enc_class, \
- .capabilities = AV_CODEC_CAP_DR1 | AV_CODEC_CAP_DELAY __VA_ARGS__, \
+ .capabilities = AV_CODEC_CAP_DR1 | AV_CODEC_CAP_DELAY | \
+ AV_CODEC_CAP_ENCODER_CAN_FLUSH __VA_ARGS__, \
.sample_fmts = (const enum AVSampleFormat[]) { \
AV_SAMPLE_FMT_S16, \
AV_SAMPLE_FMT_U8, AV_SAMPLE_FMT_NONE \
diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index 55151a0b71..216ba3f79a 100644
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -513,6 +513,13 @@ typedef struct RcOverride{
*/
#define AV_CODEC_CAP_ENCODER_REORDERED_OPAQUE (1 << 20)
+/**
+ * This encoder can be flushed using avcodec_flush_buffers(). If this flag is
+ * not set, the encoder must be closed and reopened to ensure that no frames
+ * remain pending.
+ */
+#define AV_CODEC_CAP_ENCODER_CAN_FLUSH (1 << 21)
+
/* Exported side data.
These flags can be passed in AVCodecContext.export_side_data before
initialization.
*/
@@ -4473,13 +4480,17 @@ int avcodec_fill_audio_frame(AVFrame *frame, int
nb_channels,
int buf_size, int align);
/**
- * Reset the internal decoder state / flush internal buffers. Should be called
+ * Reset the internal codec state / flush internal buffers. Should be called
* e.g. when seeking or when switching to a different stream.
*
- * @note when refcounted frames are not used (i.e. avctx->refcounted_frames is
0),
- * this invalidates the frames previously returned from the decoder. When
- * refcounted frames are used, the decoder just releases any references it
might
- * keep internally, but the caller's reference remains valid.
+ * @note for decoders, when refcounted frames are not used
+ * (i.e. avctx->refcounted_frames is 0), this invalidates the frames previously
+ * returned from the decoder. When refcounted frames are used, the decoder just
+ * releases any references it might keep internally, but the caller's reference
+ * remains valid.
+ *
+ * @note for encoders, this function will only do something if the encoder
+ * declares support for AV_CODEC_CAP_ENCODER_CAN_FLUSH.
*/
void avcodec_flush_buffers(AVCodecContext *avctx);
diff --git a/libavcodec/decode.c b/libavcodec/decode.c
index b7ae1fbb84..d21b5461e5 100644
--- a/libavcodec/decode.c
+++ b/libavcodec/decode.c
@@ -2084,6 +2084,24 @@ void avcodec_flush_buffers(AVCodecContext *avctx)
{
AVCodecInternal *avci = avctx->internal;
+ if (av_codec_is_encoder(avctx->codec)) {
+ int caps = avctx->codec->capabilities;
+ if (!(caps & AV_CODEC_CAP_ENCODER_CAN_FLUSH)) {
+ // Only encoders that explicitly declare support for it can be
+ // flushed. Otherwise, this is a no-op.
+ av_log(avctx, AV_LOG_WARNING, "Ignoring attempt to flush encoder "
+ "that doesn't support it\n");
+ return;
+ }
+ if (caps & AV_CODEC_CAP_FRAME_THREADS) {
+ // We haven't implemented flushing for frame-threaded encoders.
+ av_log(avctx, AV_LOG_WARNING, "Ignoring attempt to flush encoder "
+ "that claims to support both flushing and frame "
+ "threading\n");
+ return;
+ }
+ }
+
avci->draining = 0;
avci->draining_done = 0;
avci->nb_draining_errors = 0;
diff --git a/libavcodec/nvenc_hevc.c b/libavcodec/nvenc_hevc.c
index 7c9b3848f1..02ece979fd 100644
--- a/libavcodec/nvenc_hevc.c
+++ b/libavcodec/nvenc_hevc.c
@@ -174,7 +174,8 @@ AVCodec ff_nvenc_hevc_encoder = {
.priv_class = &nvenc_hevc_class,
.defaults = defaults,
.pix_fmts = ff_nvenc_pix_fmts,
- .capabilities = AV_CODEC_CAP_DELAY | AV_CODEC_CAP_HARDWARE,
+ .capabilities = AV_CODEC_CAP_DELAY | AV_CODEC_CAP_HARDWARE |
+ AV_CODEC_CAP_ENCODER_CAN_FLUSH,
.caps_internal = FF_CODEC_CAP_INIT_CLEANUP,
.wrapper_name = "nvenc",
};
@@ -203,7 +204,8 @@ AVCodec ff_hevc_nvenc_encoder = {
.priv_class = &hevc_nvenc_class,
.defaults = defaults,
.pix_fmts = ff_nvenc_pix_fmts,
- .capabilities = AV_CODEC_CAP_DELAY | AV_CODEC_CAP_HARDWARE,
+ .capabilities = AV_CODEC_CAP_DELAY | AV_CODEC_CAP_HARDWARE |
+ AV_CODEC_CAP_ENCODER_CAN_FLUSH,
.caps_internal = FF_CODEC_CAP_INIT_CLEANUP,
.wrapper_name = "nvenc",
};
--
2.20.1
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