Message ID | 20200331123745.6461-7-andreas.rheinhardt@gmail.com |
---|---|
State | Superseded |
Headers | show |
Series | libavformat/mux patches | expand |
Context | Check | Description |
---|---|---|
andriy/ffmpeg-patchwork | success | Make fate finished |
On Tue, 31 Mar 2020, Andreas Rheinhardt wrote: > The documentation of av_write_frame() explicitly states that the function > doesn't take ownership of the packets sent to it; while av_write_frame() > does not directly unreference the packets after having written them, it > nevertheless modifies the packet in various ways: > 1. The timestamps might be modified either by prepare_input_packet or > compute_muxer_pkt_fields. > 2. If a bitstream filter gets applied, it takes ownership of the > reference and the side-data in the packet sent to it in av_bsf_send_packet. > In case of do_packet_auto_bsf, the end result is that the returned packet > contains the output of the last bsf in the chain. If an error happens, > an empty packet will be returned; a packet may also simply not lead to > any output (vp9_superframe). > This also implies that side data needs to be really copied and can't be > shared with the input packet. > The method choosen here minimizes copying of data: When the input isn't > refcounted and no bitstream filter is applied, the packet's data will > not be copied. > > Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com> > --- > Whether a commit like this is necessary depends upon the meaning of > "ownership" (whether not having ownership disallows one from modifying a > packet) and of the user's expectations (namely if the av_write_frame() > should attempt to not modify the user-provided packet even if it were > allowed to). Furthermore, this commit has the downside of adding an > AVPacket on the stack. > > libavformat/mux.c | 34 ++++++++++++++++++++++++++++------ > 1 file changed, 28 insertions(+), 6 deletions(-) > > diff --git a/libavformat/mux.c b/libavformat/mux.c > index 79731d3008..be7652c97b 100644 > --- a/libavformat/mux.c > +++ b/libavformat/mux.c > @@ -880,11 +880,12 @@ static int do_packet_auto_bsf(AVFormatContext *s, AVPacket *pkt) { > return 1; > } > > -int av_write_frame(AVFormatContext *s, AVPacket *pkt) > +int av_write_frame(AVFormatContext *s, AVPacket *in) > { > + AVPacket local_pkt, *pkt = &local_pkt; > int ret; > > - if (!pkt) { > + if (!in) { > if (s->oformat->flags & AVFMT_ALLOW_FLUSH) { > ret = s->oformat->write_packet(s, NULL); > flush_if_needed(s); > @@ -895,22 +896,43 @@ int av_write_frame(AVFormatContext *s, AVPacket *pkt) > return 1; > } > > + /* We don't own in, so we have to make sure not to modify it. > + * The following avoids copying in's data unnecessarily. > + * Copying side data is unavoidable as a bitstream filter > + * may change it, e.g. free it on errors. */ > + pkt->data = in->data; > + pkt->size = in->size; > + if (in->buf) { > + pkt->buf = av_buffer_ref(in->buf); > + if (!pkt->buf) > + return AVERROR(ENOMEM); > + } else { > + pkt->buf = NULL; > + } > + ret = av_packet_copy_props(pkt, in); > + if (ret < 0) > + goto fail; > + > ret = prepare_input_packet(s, pkt); > if (ret < 0) > - return ret; > + goto fail; > > ret = do_packet_auto_bsf(s, pkt); > if (ret <= 0) > - return ret; > + goto fail; > > #if FF_API_COMPUTE_PKT_FIELDS2 && FF_API_LAVF_AVCTX > ret = compute_muxer_pkt_fields(s, s->streams[pkt->stream_index], pkt); > > if (ret < 0 && !(s->oformat->flags & AVFMT_NOTIMESTAMPS)) > - return ret; > + goto fail; > #endif > > - return write_packet(s, pkt); > + ret = write_packet(s, pkt); > + > +fail: > + av_packet_unref(pkt); > + return ret; > } > LGTM, thanks. Marton
diff --git a/libavformat/mux.c b/libavformat/mux.c index 79731d3008..be7652c97b 100644 --- a/libavformat/mux.c +++ b/libavformat/mux.c @@ -880,11 +880,12 @@ static int do_packet_auto_bsf(AVFormatContext *s, AVPacket *pkt) { return 1; } -int av_write_frame(AVFormatContext *s, AVPacket *pkt) +int av_write_frame(AVFormatContext *s, AVPacket *in) { + AVPacket local_pkt, *pkt = &local_pkt; int ret; - if (!pkt) { + if (!in) { if (s->oformat->flags & AVFMT_ALLOW_FLUSH) { ret = s->oformat->write_packet(s, NULL); flush_if_needed(s); @@ -895,22 +896,43 @@ int av_write_frame(AVFormatContext *s, AVPacket *pkt) return 1; } + /* We don't own in, so we have to make sure not to modify it. + * The following avoids copying in's data unnecessarily. + * Copying side data is unavoidable as a bitstream filter + * may change it, e.g. free it on errors. */ + pkt->data = in->data; + pkt->size = in->size; + if (in->buf) { + pkt->buf = av_buffer_ref(in->buf); + if (!pkt->buf) + return AVERROR(ENOMEM); + } else { + pkt->buf = NULL; + } + ret = av_packet_copy_props(pkt, in); + if (ret < 0) + goto fail; + ret = prepare_input_packet(s, pkt); if (ret < 0) - return ret; + goto fail; ret = do_packet_auto_bsf(s, pkt); if (ret <= 0) - return ret; + goto fail; #if FF_API_COMPUTE_PKT_FIELDS2 && FF_API_LAVF_AVCTX ret = compute_muxer_pkt_fields(s, s->streams[pkt->stream_index], pkt); if (ret < 0 && !(s->oformat->flags & AVFMT_NOTIMESTAMPS)) - return ret; + goto fail; #endif - return write_packet(s, pkt); + ret = write_packet(s, pkt); + +fail: + av_packet_unref(pkt); + return ret; } #define CHUNK_START 0x1000
The documentation of av_write_frame() explicitly states that the function doesn't take ownership of the packets sent to it; while av_write_frame() does not directly unreference the packets after having written them, it nevertheless modifies the packet in various ways: 1. The timestamps might be modified either by prepare_input_packet or compute_muxer_pkt_fields. 2. If a bitstream filter gets applied, it takes ownership of the reference and the side-data in the packet sent to it in av_bsf_send_packet. In case of do_packet_auto_bsf, the end result is that the returned packet contains the output of the last bsf in the chain. If an error happens, an empty packet will be returned; a packet may also simply not lead to any output (vp9_superframe). This also implies that side data needs to be really copied and can't be shared with the input packet. The method choosen here minimizes copying of data: When the input isn't refcounted and no bitstream filter is applied, the packet's data will not be copied. Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com> --- Whether a commit like this is necessary depends upon the meaning of "ownership" (whether not having ownership disallows one from modifying a packet) and of the user's expectations (namely if the av_write_frame() should attempt to not modify the user-provided packet even if it were allowed to). Furthermore, this commit has the downside of adding an AVPacket on the stack. libavformat/mux.c | 34 ++++++++++++++++++++++++++++------ 1 file changed, 28 insertions(+), 6 deletions(-)