[FFmpeg-devel] [PATCH v4 3/3] avformat/mxfenc: prefer to use the configured metadta

[emcodem at ffastrans.com]

Am 2021-01-20 16:41, schrieb Tomas Härdin:
> ons 2021-01-20 klockan 00:27 +0100 skrev Marton Balint:
>> 
>> On Tue, 19 Jan 2021, Tobias Rapp wrote:
>> 
>> > On 18.01.2021 23:53, Tomas Härdin wrote:
>> > > lör 2021-01-16 klockan 08:43 +0800 skrev lance.lmwang at gmail.com:
>> > > > On Fri, Jan 15, 2021 at 09:43:58PM +0100, Marton Balint wrote:
>> > > > > On Fri, 15 Jan 2021, Tomas Härdin wrote:
>> > > > > > Again, why? If you have a company that maintains a fork of FFmpeg then
>> > > > > > compile that info in here instead. Compare with FFmbc which always puts
>> > > > > > "FFmbc" as CompanyName.
>> > > > >
>> > > > > And how can a product based on libavformat set the company name, product
>> > > > > name and product version? It seems a valid use case for me that these are
>> > > > > overridable. Also note that this product version is only the "user
>> > friendly"
>> > > > > version string, for the numeric version still LIBAVFORMAT_VERSION values
>> > are
>> > > > > used.
>> > > >
>> > > > Yes, my use case is the product is using libavformat as library, so it's
>> > > > prefer to have way to override these information as requirements.
>> > >
>> > > What I'm worried about here is that we're going to get files which
>> > > claim to have been written by something other than libavformat. I've
>> > > had situations like this before, and it is a source of headache. For
>> > > example, if mxfenc writes some field incorrectly then this might cause
>> > > us to hack mxfdec to accept that field instead of fixing mxfenc.
>> >
>> > I agree that especially for the MXF format with its flexible structure
>> > it is more relevant to know the muxing library rather than the hosting
>> > application. Have seen MXF output files of other commercial products
>> > that also contain library identifiers like "libMXF" or "MXFtk" here.
>> >
>> > Other formats in FFmpeg use the "encoder" metadata key for embedding
>> > library information in the output file. A quick test with AVI output
>> > shows that this metadata is generated internally and cannot be
>> > overridden on the command-line.
>> 
>> If your concern is being able to identify our mxf muxer, then why not 
>> use
>> the Platform metadata item for this?
>> 
>> "Human readable name of the toolkit and operating system used. Best
>> practice is to use the form “SDK name (OS name)”"

Uhm guys, it is very bad practice: if you just insert a different 
manufacturer name then you just cheat. SMPTE 377 has a clear statement 
about what goes to the identification, you cannot just write the infos 
from a different program there.

What you can do instead is to push both identifications, the old one and 
the one from the current program into the identification array, this way 
the processing chain can be reconstructed. Unforutnately i have never 
seen anyone doing this besides Opencube.

Also, note that broadcasters currently are using the identification 
string, looking for "ffmpeg" in order to sort out non compatible XDCAMHD 
mxf: ffmpeg does not write some mandatory metadata fields as mentioned 
here: https://trac.ffmpeg.org/ticket/5097 this leads to sony devices not 
accepting the ffmpeg mxf container - which again leads to ffmpeg mxf 
wrapper for XDCAMHD not being accepted by our public broadcaster.