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Fix erractic timecode detection when extracting LTC from video 

Some music using square waves can inadvertently be interpreted as valid
LTC frame. However the encoded data is not a valid timecode, which can
lead huge A/V offsets, or other issues.
This commit is contained in:
Robin Gareus 2022-09-03 21:31:47 +02:00
parent 8af793a44d
commit 9697187037
3 changed files with 21 additions and 6 deletions
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3
libs/ardour/ardour/ltc_file_reader.h
View File

@ -38,7 +38,7 @@ public:
void write (float const*, samplecnt_t n_samples, samplepos_t pos = -1);
void raw_write (ltcsnd_sample_t*, size_t, ltc_off_t);
samplepos_t read (uint32_t& hh, uint32_t& mm, uint32_t& ss, uint32_t& ff);
samplepos_t read (uint32_t& hh, uint32_t& mm, uint32_t& ss, uint32_t& ff, samplecnt_t& len);
private:
LTCDecoder* _decoder;
@ -79,6 +79,7 @@ private:
LTCReader* _reader;
float* _interleaved_audio_buffer;
samplecnt_t _samples_read;
float _apv;
};

22
libs/ardour/ltc_file_reader.cc
View File

@ -83,7 +83,7 @@ LTCReader::raw_write (ltcsnd_sample_t* buf, size_t size, ltc_off_t off)
}
samplepos_t
LTCReader::read (uint32_t& hh, uint32_t& mm, uint32_t& ss, uint32_t& ff)
LTCReader::read (uint32_t& hh, uint32_t& mm, uint32_t& ss, uint32_t& ff, samplecnt_t& ll)
{
LTCFrameExt ltc_frame;
if (0 == ltc_decoder_read (_decoder, &ltc_frame)) {
@ -96,6 +96,8 @@ LTCReader::read (uint32_t& hh, uint32_t& mm, uint32_t& ss, uint32_t& ff)
mm = stime.mins;
ss = stime.secs;
ff = stime.frame;
ll = ltc_frame.off_end - ltc_frame.off_start;
return ltc_frame.off_start;
}
@ -108,6 +110,7 @@ LTCFileReader::LTCFileReader (std::string path, double expected_fps, LTC_TV_STAN
, _reader (0)
, _interleaved_audio_buffer (0)
, _samples_read (0)
, _apv (1920)
{
memset (&_info, 0, sizeof (_info));
assert (Glib::file_test (_path, Glib::FILE_TEST_EXISTS));
@ -116,7 +119,7 @@ LTCFileReader::LTCFileReader (std::string path, double expected_fps, LTC_TV_STAN
throw failed_constructor ();
}
const int apv = rintf (_info.samplerate / _expected_fps);
_apv = _info.samplerate / _expected_fps;
#if 0 // TODO allow to auto-detect
if (expected_fps == 25.0) {
@ -129,7 +132,7 @@ LTCFileReader::LTCFileReader (std::string path, double expected_fps, LTC_TV_STAN
_ltc_tv_standard = LTC_TV_FILM_24;
}
#endif
_reader = new LTCReader (apv, _ltc_tv_standard);
_reader = new LTCReader (rintf (_apv), _ltc_tv_standard);
}
LTCFileReader::~LTCFileReader ()
@ -208,8 +211,19 @@ LTCFileReader::read_ltc (uint32_t channel, uint32_t max_frames)
Timecode::Time timecode (_expected_fps);
samplepos_t off_start;
samplecnt_t ltc_length;
while ((off_start = _reader->read (timecode.hours, timecode.minutes, timecode.seconds, timecode.frames, ltc_length)) >= 0) {
/* sanity check */
if (timecode.hours > 23 || timecode.minutes > 60 || timecode.seconds > 60) {
continue;
}
float speed = ltc_length / _apv;
if (speed > 5 || speed < 0.2) {
continue;
}
while ((off_start = _reader->read (timecode.hours, timecode.minutes, timecode.seconds, timecode.frames)) >= 0) {
int64_t sample = 0;
Timecode::timecode_to_sample (
timecode, sample, false, false,

2
share/scripts/ltc_reader.lua
View File

@ -28,7 +28,7 @@ function dsp_run (ins, outs, n_samples)
local rv
repeat
local tc
rv, tc = ltc_reader:read (0, 0, 0, 0)
rv, tc = ltc_reader:read (0, 0, 0, 0, 0)
if rv >= 0 then
timeout = 0
self:shmem():atomic_set_int (0, 1)