Hi Tomas On Fri, Jun 13, 2025 at 12:55:56PM +0200, Tomas Härdin wrote: > Hi > > In my fiddling with fragmented indexes in mov.c I ran cross > mov_fix_index(), which has been in the codebase since September 2016. > The intent of this function is to implement limited support for edit > lists (elst). More rudely one could say it implements half-assed > support for edit lists. Besides the way it's implemented being > incredibly cursed, I feel strongly that this is not something that a > demuxer should do, partly because it's not something a demuxer *can* > do. There are a number of reasons why: > > 1) demuxers are not part of the presentation layer > 2) the demuxer must lie about what the file actually contains > 3) the ISOBMFF spec mandates being able to cut on samples, not just > frames. for audio, there is no way to do that from a demuxer > 4) similarly, there is no way (I think) to implement "dwell" segments > > The second point becomes painfully clear when one looks at > mov_fix_index(). FFStream.index_entries is completely replaced. The > function is not idempotent. For the kind of work I'm doing right now > this is a huge problem. > > As I see it, the way forward is: >
> 1) introduce API for edit lists, so that users can decide themselves > what to do +1 > 2) implement basic support for edit lists in the ffmpeg CLI +1 > 3) remove edit list hacks from all demuxers, especially mov.c +1 (with ABI +2 bump) > > The main issue I see with this is that it risks turning ffmpeg into an > NLE tool, If ffmpeg could do NLE, that would not be a bad thing And a full implementation of edit lists may be equivalent to this. I think thats a win not a loss [...] > If this stuff is done correctly then it should be possible to remux MOV > to MXF while keeping the edit lists and the original uncut essence. And > of course back again to MOV if so desired. yeah > > I haven't sketched out any API yet, but it would probably closely > mirror how elst works in MOV. Care should be taken that MXF operational > pattern 3a can also fit into this API. Possibly even OP3c. > > Thoughts? it would be cool if someone implemented this, its not trivial as all sides need to support it. demuxer, muxer, player, ffmpeg thx [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB What is money laundering? Its paying someone and not telling the government.
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