Soft Works: > > >> -----Original Message----- >> From: ffmpeg-devel <ffmpeg-devel-boun...@ffmpeg.org> On Behalf Of Andreas >> Rheinhardt >> Sent: Wednesday, 22 September 2021 04:43 >> To: ffmpeg-devel@ffmpeg.org >> Subject: Re: [FFmpeg-devel] [PATCH v8 12/13] avfilter/split_cc: Add split_cc >> filter for closed caption handling >> >> Soft Works: >>> >>> >>>> -----Original Message----- >>>> From: ffmpeg-devel <ffmpeg-devel-boun...@ffmpeg.org> On Behalf Of Andreas >>>> Rheinhardt >>>> Sent: Wednesday, 22 September 2021 04:18 >>>> To: ffmpeg-devel@ffmpeg.org >>>> Subject: Re: [FFmpeg-devel] [PATCH v8 12/13] avfilter/split_cc: Add >> split_cc >>>> filter for closed caption handling >>>> >>>>> This is a good question, as to whether it is safe to assume that the >>>>> filter's lifetime doesn't end before the last frame has been processed. >>>>> I thought it would be? >>>> >>>> So the frames are supposed to be never forwarded to the user? Or is the >>>> user supposed to stop using these frames after the filter's lifetime >> ended? >>> >>> >>> The subtitle_header is global and is constant across all frames. >>> A resulting media file has only a (= the) single "subtitle header". >>> (it's not like a "header for each subtitle line or event"). >>> >> >> Who ensures that it is constant across all frames? What happens if one >> mixes frames from two different sources? And who owns the subtitle header? > > In cases when the subtitle stream originates from a decoder and frames > are submitted into the filtergraph, ffmpeg.c makes a copy of it (field > of AVCodecContext) and stores it in InputStream->subtitle_heartbeat->subtitle > header > and stores the pointer to this in each subtitle frame. > It gets freed during ffmpeg uninit. > > In cases when the subtitle stream originates from a filter like split_cc > or graphicsubs2text, the filter creates the header and owns it, and stores > the reference in each subtitle frame it produces. > It gets freed during filter uninit. > > Relevant is the subtitle_header of the first frame that arrives at a target. > A target can be an encoder at the end of the filtergraph or other filters > like overlay_textsubs. > > Any filters in-between may use the subtitle_header for reference when > performing certain manipulations, but are not allowed (meant to) modify it. >
If a frame or packet is refcounted, the lifetime of the data contained (or rather referenced) by it is indefinite; it survives closing a demuxer/encoder (for packets) or a decoder (for frames). I might have trouble making sense of the timestamp if I close the demuxer and the AVStream (with the timebase) it came from, but I still have the data. This is not so with this field; it is supposed to be not modified by the owner of an AVFrame, yet it is not even a const char*. Worse, it's lifetime is tied in a completely unclear way to something else. This is just not going to work. - Andreas _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
