# Subject: concat loses 2 frames or freezes up video

# The trimmed input files *_t* were created this way:
# The next 4 plus 2 lines are the commands executed by an old (but stable and proven) script to trim movie files 
mplayer -vc nul -vo nul -ao pcm 20141107_4horses-scatter-cows_mini1355.mov
mv audiodump.wav 20141107_4horses-scatter-cows_mini1355_t.wav
ffmpeg-0.5 -ss 2 -t 13 -i 20141107_4horses-scatter-cows_mini1355_t.wav -acodec copy 20141107_4horses-scatter-cows_mini1355_t2-13.wav
ffmpeg-0.5 -ss 2 -t 13 -i 20141107_4horses-scatter-cows_mini1355.mov -vcodec copy -i 20141107_4horses-scatter-cows_mini1355_t2-13.wav -acodec copy -map 0:0 -map 1:0 20141107_4horses-scatter-cows_mini1355_t2-13.mov

ffmpeg-0.5 -ss 15 -t 9 -i 20141107_4horses-scatter-cows_mini1355_t.wav -acodec copy 20141107_4horses-scatter-cows_mini1355_t15-9.wav
ffmpeg-0.5 -ss 15 -t 9 -i 20141107_4horses-scatter-cows_mini1355.mov -vcodec copy -i 20141107_4horses-scatter-cows_mini1355_t15-9.wav -acodec copy -map 0:0 -map 1:0 20141107_4horses-scatter-cows_mini1355_t15-9.mov

#  I'm using the above file(s) instead of actual loop-recording 3-minute "3:01 minus 1 sec" files to keep it simple and presentable.
# Description: I had the cows all rounded up, but these 4 loose horses came running down the hill and scattered the herd.
# The above trim equivilant one-step with newer ffmpeg
ffmpeg-2.4 -i 20141107_4horses-scatter-cows_mini1355.mov -ss 13 -t 3 -c copy 20141107_4horses-scatter-cows_mini1355_c13-3.mov

# The resulting trims or clips seem correct in the number of frames and seconds in length. No actual frames missing.
#  but the audio from ffmpeg-0.5 resulted in length of 13.056 seconds, whereas ffmpeg-2.4 does better with length of 13.000 seconds, in the 13 second example.

# Test #1, concat of two trimmed files results in loss of 2 frames at end of first file
# Contents of file: concat-list1.txt The following 2 lines.
file '20141107_4horses-scatter-cows_mini1355_t2-13.mov'
file '20141107_4horses-scatter-cows_mini1355_t15-9.mov'
#_EOF

ffmpeg -f concat -i concat-list1.txt -c copy 20141107_test1-loses2frames.mov

# test 2, concat of one trimmed file and original file results in video freezing up, appears to be a video or audio mis-match
# concat-list2.txt
file '20141107_4horses-scatter-cows_mini1355_t2-13.mov'
file '20141107_4horses-scatter-cows_mini1355.mov'
#_EOF

ffmpeg -f concat -i concat-list2.txt -c copy 20141107_test2-freezes.mov

# test 3, concat of clipped and original results in many errors, wrong time length, and video freezing up interspersed with stopped audio
# concat-list3.txt
file '20141107_4horses-scatter-cows_mini1355_c13-3.mov'
file '20141107_4horses-scatter-cows_mini1355.mov'
#_EOF

ffmpeg -f concat -i concat-list3.txt -c copy 20141107_test3-fails.mov

The input files above, can be found at:
 http://seahorseCorral.org/videos/tests/20141107_4horses-scatter-cows_mini1355.mov
 http://seahorseCorral.org/videos/tests/20141107_4horses-scatter-cows_mini1355_t2-13.mov
 http://seahorseCorral.org/videos/tests/20141107_4horses-scatter-cows_mini1355_t15-9.mov
 http://seahorseCorral.org/videos/tests/20141107_4horses-scatter-cows_mini1355_c13-3.mov

# In depth analysis:
# #1. 20141107_test1-loses2frames.mov
#  notice clock advances 1 second at frame# 30 (of 1-30), and time position advances one frame afterward (frame# 1 or 31,61,91...)
#  at time 0:14, the joint, now the clock in lower left is advancing one frame afterward.
#  count only 28 frames from 0:13.0 to 0:13.999

# trying varying time lengths and start positions sometimes results in only 1 frame lost.

# #2. 20141107_test2-freezes.mov
#  plays okay until 0:12.97 when video does not advance to 0:13.00 , audio continues 
#  if press right arrow to advance in time, video starts updating again at 4:21 but at slow frame rate
#  so I conclude the problem is possibly in reading the time length of the clips when the concat operation is performed.
#  reaches end at or around 21:11 . If it were being encoded to 1 frame per second, the length should be 27 minutes. Something else then...

# #3. 20141107_test3-fails.mov
#  output has many warnings during ffmpeg command. totals 1620 frames in 54 seconds. correct.
#  extracting the audio track afterward, is also correct, 54.000 seconds.
#  playback is okay until 0:02.99 when video continues at an accelerated rate without any audio, and time position stays stuck at 0:02
#  after 13 clock seconds, audio starts playback for a couple seconds, then stutters badly with several seconds between audio "bursts" or segments.

# on a brighter note, it looks like the clips made with ffmpeg-2.4 and then concat-ed together, are looking good and correct. So tests 1 and 2 look like "compatibility issues" with older files or format packaging, and the #3 is a still current bug.

# I tried #1 again with .avi as the output extension. 30 frames. No lost frames. So the problem can localized to .mov I think.
# Trying #2 again with avi plus mov for inputs and avi as output... same result, so looks like the .mov file is the common problem.
# re-wrapping the original mov into avi and repeating test #2, did not help. So the wrapper is less the issue, and the h264 stream is the problem, I think.

# Tests have now been repeated with newest ffmpeg by git pull and re-compile fresh on 2014-12-07 15:00 PST

# Output from ffmpeg with -v 9 -loglevel 99 is long, therefore is provided in separate files at:
 http://seahorseCorral.org/videos/tests/ffmpeg-concat-test1.log.gz
 http://seahorseCorral.org/videos/tests/ffmpeg-concat-test2.log.gz
 http://seahorseCorral.org/videos/tests/ffmpeg-concat-test3.log.gz

# One interesting warning is only in #3
[mov @ 0x95522c0] timecode: tbc=19200/1 invalid, fallback on 30/1