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avcodec/h264, videotoolbox: fix crash after VT decoder fails

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The way videotoolbox hooks in as a hwaccel is pretty hacky. The VT decode
API is not invoked until end_frame(), so alloc_frame() returns a dummy
frame with a 1-byte buffer. When end_frame() is eventually called, the
dummy buffer is replaced with the actual decoded data from
VTDecompressionSessionDecodeFrame().

When the VT decoder fails, the frame returned to the h264 decoder from
alloc_frame() remains invalid and should not be used. Before
9747219958, it was accidentally being
returned all the way up to the API user. After that commit, the dummy
frame was unref'd so the user received an error.

However, since that commit, VT hwaccel failures started causing random
segfaults in the h264 decoder. This happened more often on iOS where the
VT implementation is more likely to throw errors on bitstream anomolies.
A recent report of this issue can be see in
http://ffmpeg.org/pipermail/libav-user/2016-November/009831.html

The issue here is that the dummy frame is still referenced internally by the
h264 decoder, as part of the reflist and cur_pic_ptr. Deallocating the
frame causes assertions like this one to trip later on during decoding:

  Assertion h->cur_pic_ptr->f->buf[0] failed at src/libavcodec/h264_slice.c:1340

With this commit, we leave the dummy 1-byte frame intact, but avoid returning it
to the user.

This reverts commit 9747219958.

Signed-off-by: wm4 <nfxjfg@googlemail.com>
This commit is contained in:
Aman Gupta 2017-02-21 10:48:37 -08:00 committed by wm4
parent 734d760e2f
commit b6eaa3928e
4 changed files with 8 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
libavcodec/h264_refs.c
View File

@ -571,8 +571,7 @@ void ff_h264_remove_all_refs(H264Context *h)
if (h->short_ref_count && !h->last_pic_for_ec.f->data[0]) {
ff_h264_unref_picture(h, &h->last_pic_for_ec);
if (h->short_ref[0]->f->buf[0])
ff_h264_ref_picture(h, &h->last_pic_for_ec, h->short_ref[0]);
ff_h264_ref_picture(h, &h->last_pic_for_ec, h->short_ref[0]);
}
for (i = 0; i < h->short_ref_count; i++) {

7
libavcodec/h264dec.c
View File

@ -850,7 +850,12 @@ static int output_frame(H264Context *h, AVFrame *dst, H264Picture *srcp)
AVFrame *src = srcp->f;
const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(src->format);
int i;
int ret = av_frame_ref(dst, src);
int ret;
if (src->format == AV_PIX_FMT_VIDEOTOOLBOX && src->buf[0]->size == 1)
return AVERROR_EXTERNAL;
ret = av_frame_ref(dst, src);
if (ret < 0)
return ret;

2
libavcodec/version.h
View File

@ -29,7 +29,7 @@
#define LIBAVCODEC_VERSION_MAJOR 57
#define LIBAVCODEC_VERSION_MINOR 82
#define LIBAVCODEC_VERSION_MICRO 100
#define LIBAVCODEC_VERSION_MICRO 101
#define LIBAVCODEC_VERSION_INT AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \
LIBAVCODEC_VERSION_MINOR, \

2
libavcodec/videotoolbox.c
View File

@ -352,8 +352,6 @@ static int videotoolbox_common_end_frame(AVCodecContext *avctx, AVFrame *frame)
AVVideotoolboxContext *videotoolbox = avctx->hwaccel_context;
VTContext *vtctx = avctx->internal->hwaccel_priv_data;
av_buffer_unref(&frame->buf[0]);
if (!videotoolbox->session || !vtctx->bitstream)
return AVERROR_INVALIDDATA;