Hello,
One of our applications uses the QuickTime API to extract uncompressed
video frames from files supported by QuickTime. A couple of files in my
test batch are 3GP files containing H.263 video w/AMR nb audio. Under
QuickTime 6.x these files presented no problems. Since upgrading to
QT7, this is no longer the case.
The trouble I'm experiencing is fairly straightforward. Attempts to
seek within the video stream report success, but when I attempt to get
the video data I receive the first frame's decoded data no matter what
value I pass to SetMovieTimeValue(), and at this point I can't determine
what I'm doing wrong.
Here's the relevant source code:
// the_movie: movie handle from NewMovieFromFile()
// index: TimeValue in movie's time scale
// set time...
SetMovieTimeValue( the_movie, index);
UpdateMovie( the_movie);
MoviesTask( the_movie, 0);
// FYI: at this point, a call to GetMovieTimeValue returns index,
// as expected
// values for FCompressImage args:
// bounds = m_pixMap bounds; m_pixMap bounds same as the video source
// depth is 24 in this case
// spatial_quality = codecMaxQuality
// codec_type = kBMPCodecType
// the_codec = anyCodec
// buffer size is the size reported by a call to GetMaxCompressionSize
using
// the same parameters passed to FCompressImage; not that it really
matters...
// image_desc was just alloc'd via a call to NewHandleClear
FCompressImage(m_pixMap, &bounds, depth, spatial_quality,
codec_type, the_codec, 0, 0, 0, 0, 0,
image_desc, buffer.GetBuffer());
At this point I'm expecting my buffer to contain data from the nearest
time to that which I passed to SetMovieTimeValue. When QT6 is present
on the test PC, I get what I'm expecting. When QT7 is present, I get
frame 0. Every time. This code works fine for every other file
imported via QuickTime that I've encountered.
Notes on my .3gp files:
- both .3gp files that show this problem contain H.263 video w/AMR-nb
audio,
as stated above
- both .3gp files with this problem show timescales of 1000 for the
movie, and
48000 for the video track media
The .3gp files that don't exhibit this problem have matching time scales
for the movie and video track media. If this is the source of the
problem, what must I do to remedy it (QT docs currently state that QT
will handle time scale differences for me, is that really the case or an
oversight?)? I have attempted adjusting track media time scale to match
the movie time scale, and vice versa to no avail. I have also attempted
adjusting the index value passed to SetMovieTimeValue to be in video
track media timescale; also no change, and I would think this is invalid
anyway.
Has anyone else seen this problem? Is there a work around?
Thanks in advance for any help anyone can provide.
Regards,
tom
