[FFmpeg-devel] Gaining access to a encoder context in avformat?

[Kevin Wheatley]

Please excuse my newbie knowledge of the code base BTW...

I've just done a simple test

ffmpeg -color_range mpeg -i test_charts/test_encoding.tif -c dnxhd -vb
115M  /quicktimes/ffmpeg_test.mov

During this the vos_data contains...

00 00 02 80 01 01 80 A0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 04 38 07 80 00 04 38 00 00 38 88 ...

Which looks to me like the start of the VC3/DNxHD bit stream and in
this case the code puts valid data in the header atoms.

If I then

fmpeg -i quicktimes/ffmpeg_test.mov -c copy quicktimes/ffmpeg_test_copy.mov

the vos_data instead contains

00 00 00 18 41 43 4C 52 41 43 4C 52 30 30 30 31 00 00 00 01 00 00 00
00 00 00 00 18 41 50 52 47 41 50 52 47 ...

which is the  start of the Avid atoms from the incomming Quicktime.

So I could peak into the stream and 'guess' based on the content being
0x00, 0x00, 0x02, 0x80, 0x01  that we are encoding and can trust the
contents, else I could search through looking for the atom via the
string "ARESARES" and then having located it I could assume to use
that. The only oddball case is if it is not found, at that point the
code needs to know if it is interlaced as well as the avid codec
identifier, or maybe that is the point at which we 'give up' and fail
with unsupported?

Kevin