import os from math import inf from .common import PostProcessor from ..utils import prepend_extension from ..mp4_parser import ( write_mp4_boxes, parse_mp4_boxes, pack_be32, pack_be64, unpack_ver_flags, unpack_be32, unpack_be64, ) class MP4FixupTimestampPP(PostProcessor): @property def available(self): return True def analyze_mp4(self, filepath): """ returns (baseMediaDecodeTime offset, sample duration cutoff) """ smallest_bmdt, known_sdur = inf, set() with open(filepath, 'rb') as r: for btype, content in parse_mp4_boxes(r): if btype == 'tfdt': version, _ = unpack_ver_flags(content[0:4]) # baseMediaDecodeTime always comes to the first if version == 0: bmdt = unpack_be32(content[4:8]) else: bmdt = unpack_be64(content[4:12]) if bmdt == 0: continue smallest_bmdt = min(bmdt, smallest_bmdt) elif btype == 'tfhd': version, flags = unpack_ver_flags(content[0:4]) if not flags & 0x08: # this box does not contain "sample duration" continue # https://github.com/gpac/mp4box.js/blob/4e1bc23724d2603754971abc00c2bd5aede7be60/src/box.js#L203-L209 # https://github.com/gpac/mp4box.js/blob/4e1bc23724d2603754971abc00c2bd5aede7be60/src/parsing/tfhd.js sdur_start = 8 # header + track id if flags & 0x01: sdur_start += 8 if flags & 0x02: sdur_start += 4 # the next 4 bytes are "sample duration" sample_dur = unpack_be32(content[sdur_start:sdur_start + 4]) known_sdur.add(sample_dur) maximum_sdur = max(known_sdur) for multiplier in (0.7, 0.8, 0.9, 0.95): sdur_cutoff = maximum_sdur * multiplier if len(set(x for x in known_sdur if x > sdur_cutoff)) < 3: break else: sdur_cutoff = inf return smallest_bmdt, sdur_cutoff @staticmethod def transform(r, bmdt_offset, sdur_cutoff): for btype, content in r: if btype == 'tfdt': version, _ = unpack_ver_flags(content[0:4]) if version == 0: bmdt = unpack_be32(content[4:8]) else: bmdt = unpack_be64(content[4:12]) if bmdt == 0: yield (btype, content) continue # calculate new baseMediaDecodeTime bmdt = max(0, bmdt - bmdt_offset) # pack everything again and insert as a new box if version == 0: bmdt_b = pack_be32(bmdt) else: bmdt_b = pack_be64(bmdt) yield ('tfdt', content[0:4] + bmdt_b + content[8 + version * 4:]) continue elif btype == 'tfhd': version, flags = unpack_ver_flags(content[0:4]) if not flags & 0x08: yield (btype, content) continue sdur_start = 8 if flags & 0x01: sdur_start += 8 if flags & 0x02: sdur_start += 4 sample_dur = unpack_be32(content[sdur_start:sdur_start + 4]) if sample_dur > sdur_cutoff: sample_dur = 0 sd_b = pack_be32(sample_dur) yield ('tfhd', content[:sdur_start] + sd_b + content[sdur_start + 4:]) continue yield (btype, content) def modify_mp4(self, src, dst, bmdt_offset, sdur_cutoff): with open(src, 'rb') as r, open(dst, 'wb') as w: write_mp4_boxes(w, self.transform(parse_mp4_boxes(r))) def run(self, information): filename = information['filepath'] temp_filename = prepend_extension(filename, 'temp') self.write_debug('Analyzing MP4') bmdt_offset, sdur_cutoff = self.analyze_mp4(filename) working = inf not in (bmdt_offset, sdur_cutoff) # if any of them are Infinity, there's something wrong # baseMediaDecodeTime = to shift PTS # sample duration = to define duration in each segment self.write_debug(f'baseMediaDecodeTime offset = {bmdt_offset}, sample duration cutoff = {sdur_cutoff}') if bmdt_offset == inf: # safeguard bmdt_offset = 0 self.modify_mp4(filename, temp_filename, bmdt_offset, sdur_cutoff) if working: self.to_screen('Duration of the file has been fixed') else: self.report_warning(f'Failed to fix duration of the file. (baseMediaDecodeTime offset = {bmdt_offset}, sample duration cutoff = {sdur_cutoff})') os.replace(temp_filename, filename) return [], information