On Thu, Feb 13, 2025, 22:04 Andreas Rheinhardt < andreas.rheinha...@outlook.com> wrote:
> Pavel Koshevoy: > > The problem is reproducible with "Test for Quicktime 608 CC file.mov" > > from https://samples.ffmpeg.org/MPEG2/subcc/ > > > > ffmpeg -i "Test for Quicktime 608 CC file.mov" -map 0 -c copy -y > remuxed.mov > > > > Prior to the fix QuickTime Player playback of remuxed.mov would > > render garbage text for "English CC" subtitles. > > Is remuxing necessary for there being garbage? > The original file displays correct English CC text in QuickTime Player, and the remuxed file (prior to the fix) does not. > > --- > > libavformat/mov.c | 70 +++++++++++++++++++++++++++++++++++++++-------- > > 1 file changed, 59 insertions(+), 11 deletions(-) > > > > diff --git a/libavformat/mov.c b/libavformat/mov.c > > index 85aef33b19..5a91ef5b8c 100644 > > --- a/libavformat/mov.c > > +++ b/libavformat/mov.c > > @@ -10788,25 +10788,73 @@ static int mov_change_extradata(AVStream *st, > AVPacket *pkt) > > return 0; > > } > > > > -static int get_eia608_packet(AVIOContext *pb, AVPacket *pkt, int size) > > +static int get_eia608_packet(AVIOContext *pb, AVPacket *pkt, int > src_size) > > { > > - int new_size, ret; > > + /* We can't make assumptions about the structure of the payload, > > + because it may include multiple cdat and cdt2 samples. */ > > + const uint32_t cdat = AV_RB32("cdat"); > > + const uint32_t cdt2 = AV_RB32("cdt2"); > > I don't think that using (non-variable) variables for these improves > clarity (e.g. it means that the definition of the actual values used for > the comparisons below is now further away from its use). Why not simply > use MKBETAG('c','d','a','t') below? > That is a matter of personal preference. I personally find "cdat" more readable (and searchable) than any MKBETAG. > > + int ret, out_size = 0; > > > > - if (size <= 8) > > + /* a valid payload must have size, 4cc, and at least 1 byte pair: */ > > + if (src_size < 10) > > return AVERROR_INVALIDDATA; > > - new_size = ((size - 8) / 2) * 3; > > - ret = av_new_packet(pkt, new_size); > > + > > + /* avoid an int overflow: */ > > + if ((src_size - 8) / 2 >= INT_MAX / 3) > > + return AVERROR_INVALIDDATA; > > + > > + ret = av_new_packet(pkt, ((src_size - 8) / 2) * 3); > > if (ret < 0) > > return ret; > > > > - avio_skip(pb, 8); > > - for (int j = 0; j < new_size; j += 3) { > > - pkt->data[j] = 0xFC; > > - pkt->data[j+1] = avio_r8(pb); > > - pkt->data[j+2] = avio_r8(pb); > > + /* parse and re-format the c608 payload in one pass. */ > > + while (src_size >= 10) { > > + const uint32_t atom_size = avio_rb32(pb); > > + const uint32_t atom_type = avio_rb32(pb); > > + const uint32_t data_size = atom_size - 8; > > This may wrap around (if atom_size is < 8). If int is 32 bits, then the > data_size > src_size check will catch this, but in case of 64 bit ints > it may not. Relying on (unsigned, defined) integer wraparound should be > avoided unless it is advantageous to use it; in this case, this is just > not true: Just compare atom_size to 10 below. > I fully expect the size of uint32_t to be 32 bits, on any platform. It should be a compile time assertio n, but that is outside the scope of this fix. The name of the data type says it's 32 bit long, so it must be so. > > + const uint8_t cc_field = > > + atom_type == cdat ? 1 : > > + atom_type == cdt2 ? 2 : > > + 0; > > + > > + /* account for bytes consumed for atom size and type. */ > > + src_size -= 8; > > + > > + /* make sure the data size stays within the buffer boundaries. > */ > > + if (data_size < 2 || data_size > src_size) { > > + ret = AVERROR_INVALIDDATA; > > + break; > > + } > > + > > + /* make sure the data size is consistent with N byte pairs. */ > > + if (data_size % 2 != 0) { > > We typically try to avoid redundant "!= 0". > Again, this is a matter of personal preference. If you would prefer to tweak the patch to suit your personal preference before merging -- you are free to do so, but I don't think it's a valid reason to delay a fix for a parser that has been mis-parsing well-formed files for the past 5 years. > > + ret = AVERROR_INVALIDDATA; > > + break; > > + } > > + > > + if (!cc_field) { > > + /* neither cdat or cdt2 ... skip it */ > > + avio_skip(pb, data_size); > > + src_size -= data_size; > > + continue; > > + } > > + > > + for (int32_t i = 0; i < data_size; i += 2) { > > int32_t? Why signed? (And why use a separate loop counter at all? Simply > decrement data_size by 2 in each iteration. > Please feel free to make additional improvements to whatever fix you decide to merge. > > + pkt->data[out_size] = (0x1F << 3) | (1 << 2) | (cc_field - > 1); > > + pkt->data[out_size + 1] = avio_r8(pb); > > + pkt->data[out_size + 2] = avio_r8(pb); > > + out_size += 3; > > + src_size -= 2; > > + } > > } > > > > - return 0; > > + if (src_size > 0) > > + /* skip any remaining unread portion of the input payload */ > > + avio_skip(pb, src_size); > > + > > + av_shrink_packet(pkt, out_size); > > + return ret; > > } > > > > static int mov_finalize_packet(AVFormatContext *s, AVStream *st, > AVIndexEntry *sample, > > Generally, I believe that reading the input into pkt->data[size / 2] > would be advantageous: It would make it simple to check for EOF and I/O > errors (notice that the avio_r* reads above are unchecked) and would > read the data in one go, avoiding all the avio_skip(). > > - Andreas > > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel > > To unsubscribe, visit link above, or email > ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe". > _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
