[FFmpeg-devel] [PATCH] avformat/mux: skip parameter and pts checks for data muxer

[Gyan]

On 02-05-2019 03:23 PM, Nicolas George wrote:
> Gyan (12019-04-28):
>> b) ffmpeg will call avformat_write_header for the output, which will likely
>> fail because of the aforementioned codec parameter issues.
> Are you sure? It looks to me like avformat_write_header() does not
> perform checks by itself, and null does not either.

The flow is

avformat_write_header -> avformat_init_output -> init_muxer

And in the last function, lines 293-385 (as of 7eba26451) carry out the 
checks, and which my patch skips.

>> The pipeline for dumping damaged streams is identical to dumping valid
>> streams except for the part when timestamps are regulated and codec fields
>> validated for the target muxer, which is what my patch disables for a single
>> muxer that doesn't need them. I don't see much (any?) "wasted" processing
>> with my patch, relative to streamcopying a valid stream.
> The problem is not about waste as a performance issue, the problem is
> about complexity as a maintenance issue. Exceptions are expensive in
> that regard.

The problem is that there is no clean set of flags which isolate the 
parameter-agnostic muxers - not surprising as this is a library for 
making valid media files. A new flag could be invented, if the present 
patch is too idiosyncratic. On a related note, as I mentioned elsewhere 
in this thread, an existing flag AVFMT_NOTIMESTAMPS, which in theory I 
could use, is of no help here, as it has been set for muxers which do 
handle timestamps in some way.

Gyan