Help converting flv1 files (Sorenson) to mp4 using ffmpeg

[chesapeake]

Hi all,

I'm converting flv files captured from rtmp streams to mp4 using ffmpeg.

Here are the command line parameters i'm using:

ffmpeg -i "%%a" -c:v libx264 -preset superfast -c:a libvo_aacenc -b:a 128k "mp4s\%%~na.mp4"

This works great when the captured files are encoded with AVC/Speex, but unfortunately some of them are encoded with Sorenson Spark/Nellymoser. The conversion still works, sort of. But it takes forever and the resulting mp4 files are huge (4 or 5 times the size of the flv file) and jerky in playback.

Any help for fine-tuning the ffmpeg parameters to work better with the Sorenson encoded files would be much appreciated.

Thanks for your time!

[Baldrick]

Can you post the full details of one those flv? Use mediainfo(view->text) or mediainfoxp.

And set crf value to lower the file size/quality. Like -crf 25 (increase for smaller size).

[chesapeake]

Sure thing. Here are the details:

General
Complete name : G:\convert\convertToMP4\unconvertable\stream.flv
Format : Flash Video
File size : 28.1 MiB
Duration : 9mn 33s
Overall bit rate : 411 Kbps

Video
Format : Sorenson Spark
Codec ID : 2
Duration : 9mn 33s
Width : 320 pixels
Height : 240 pixels
Display aspect ratio : 4:3
Frame rate mode : Variable
Bit depth : 8 bits

Audio
Format : Nellymoser
Codec ID : 6
Duration : 9mn 33s
Channel(s) : 1 channel
Sampling rate : 11.025 KHz
Bit depth : 16 bits

[Baldrick]

It's probably the variable framerate that causes problem. You could try set a framerate with -r 30... But you will get sybc issues.

[chesapeake]

That made a huge difference, thank you! And the sync issues don't seem too bad (so far at least).

[Selur]

as a side note: one could extract the time codes using flvextract and add them later to the mp4 using mp4fpsmod. (this is the way I do it in Hybrid)