Two ffmpeg questions about "sequential" coding

Question

fmpeg

Greetings!

I encode video (avi, mkv, m4v) for ipad with the following command:

ffmpeg -i $input -r 29.97 -vcodec libx264 -flags +loop -cmp +chroma -deblockalpha 0 -deblockbeta 0 \
   -crf 21 -bt 256k -refs 1 -coder 0 -me_method full -me_range 16 -subq 5 \
   -partitions +parti4x4+parti8x8+partp8x8 -g 250 -keyint_min 25 -level 30 \
   -sc_threshold 40 -i_qfactor 0.71 -vf $scale -acodec libfaac -ab 112k \
   -ar 48000 -ac 2 -threads $threads output.mp4 

Two questions:
1. When I download the resulting file, sometimes you can open the undownloaded file for playback, and sometimes it does not open. Is it possible to get rid of the second case?

2. How to make it possible to view an unconverted file? Those. I watch the resulting fragment while the rest is added to the end of it.

Thank you.

Answer 1

Try using the qt_faststart utility after conversion, it transfers the metadata and timeline to the beginning of the file, which allows you to start playback immediately, and not after the file is completely downloaded.

Answer 2

Try VLC to watch. It starts playing almost all mp4 before the end of the download. If it does not help, you need to think about how to encode.

Answer 3

Then you should play with the key frame rate