[FFmpeg-user] How to download and transcode video stream to mp4 and save the TS stream to file at the same time?

[Gyan Doshi]

On 2024-09-30 01:29 am, Bo Berglund wrote:
> I have created a script that downloads Internet video streams (basically news
> programs) and transcodes to mp4 format with a fixed windows size.
> As soon as the video stream recording ends the mp4 file can be played.
>
> I wonder if there is a way to let ffmpeg do two things at the same time:
> - download as now but save the stream to a TS formatted file and:
> - transcode to the mp4 format into a different output file
>
> This would make it possible to start viewing the downloaded file in TS format
> while the real output file remains unplayable until the download finishes and
> the moov atom gets written.

Three months ago, ffmpeg's mov/mp4 muxer added a movflags called 
`hybrid_fragmented`

 From the doc description,

"
For recoverability - write the output file as a fragmented file. This 
allows the intermediate file to be read while being written (in 
particular, if the writing process is aborted uncleanly). When writing 
is finished, the file is converted to a regular, non-fragmented file, 
which is more compatible and allows easier and quicker seeking.

If writing is aborted, the intermediate file can manually be remuxed to 
get a regular, non-fragmented file of what had been written into the 
unfinished file.
"

Regards,
Gyan