Re: [FFmpeg-devel] [PATCH] avformat/mov: (v4) fix get_eia608_packet

[Pavel Koshevoy <pkoshevoy@gmail.com>]

On Fri, Feb 21, 2025 at 9:49 AM Pavel Koshevoy <pkoshevoy@gmail.com> wrote:

> If there are no further constructive review comments today and tomorrow
> then I will commit and push this change on Sunday (if I don't forget).
>
> Pavel.
>


Pushed in commit 5021764413a138f340ba46a9b145215b7535ea83

Pavel.




>
> On Thu, Feb 13, 2025 at 2:22 PM Pavel Koshevoy <pkoshevoy@gmail.com>
> wrote:
>
>> 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.
>> ---
>>  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");
>> +    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;
>> +        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) {
>> +            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) {
>> +            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,
>> --
>> 2.43.0
>>
>>
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