[FFmpeg-devel] [HACK] Remove MAX_STREAMS usages

[Reimar Döffinger]

On Tue, Aug 10, 2010 at 07:31:49PM +0200, Michael Niedermayer wrote:
> On Tue, Aug 10, 2010 at 01:14:56AM +0200, Aurelien Jacobs wrote:
> > On Sun, Aug 08, 2010 at 10:40:40PM +0200, Reimar D?ffinger wrote:
> > > Hello,
> > > this is just a quick hack that removes all usages of
> > > MAX_STREAMS.
> > > 
> > > [...]
> > 
> > And here are the last bits I extracted/reworked from this patch.
> > 
> > First patch in this email uses nb_streams instead of MAX_STREAMS to
> > dynamically alloc arrays in libavformat/utils.c. This is compatible
> > with both the old API and the new API.
> > 
> > Second and last patch actually add the new API, finally getting ride of
> > MAX_STREAMS. It is obviously disabled until next major bump.
> > 
> > Aurel
> >  utils.c |   37 +++++++++++++++++++++++++++----------
> >  1 file changed, 27 insertions(+), 10 deletions(-)
> > 553bd8bafb70b124e3ed2747f577f4ae057e8094  max_stream.diff
> > commit f04d73bbdcb67af2e6d1145c652a6b2978c0c83f
> > Author: Aurelien Jacobs <aurel at gnuage.org>
> > Date:   Tue Aug 10 00:21:06 2010 +0200
> > 
> >     dynamically use nb_streams instead of static use of MAX_STREAMS
> > 
> > diff --git a/libavformat/utils.c b/libavformat/utils.c
> > index 1aa965c..edd3d19 100644
> > --- a/libavformat/utils.c
> > +++ b/libavformat/utils.c
> > @@ -1871,10 +1871,13 @@ static void av_estimate_timings_from_pts(AVFormatContext *ic, int64_t old_offset
> >      AVPacket pkt1, *pkt = &pkt1;
> >      AVStream *st;
> >      int read_size, i, ret;
> > -    int64_t end_time, start_time[MAX_STREAMS];
> > +    int64_t end_time, *start_time;
> >      int64_t filesize, offset, duration;
> >      int retry=0;
> >  
> > +    if (!(start_time = av_malloc(ic->nb_streams * sizeof(*start_time))))
> > +        return;
> > +
> >      ic->cur_st = NULL;
> >  
> >      /* flush packet queue */
> > @@ -1935,6 +1938,7 @@ static void av_estimate_timings_from_pts(AVFormatContext *ic, int64_t old_offset
> >      }while(   end_time==AV_NOPTS_VALUE
> >             && filesize > (DURATION_MAX_READ_SIZE<<retry)
> >             && ++retry <= DURATION_MAX_RETRY);
> > +    av_free(start_time);
> >  
> >      fill_all_stream_timings(ic);
> >  
> > @@ -2160,15 +2164,23 @@ int av_find_stream_info(AVFormatContext *ic)
> >      int i, count, ret, read_size, j;
> >      AVStream *st;
> >      AVPacket pkt1, *pkt;
> > -    int64_t last_dts[MAX_STREAMS];
> > -    int64_t duration_gcd[MAX_STREAMS]={0};
> > -    int duration_count[MAX_STREAMS]={0};
> > +    int64_t *last_dts;
> > +    int64_t *duration_gcd;
> > +    int *duration_count;
> >      double (*duration_error)[MAX_STD_TIMEBASES];
> >      int64_t old_offset = url_ftell(ic->pb);
> > -    int64_t codec_info_duration[MAX_STREAMS]={0};
> > +    int64_t *codec_info_duration;
> >  
> > -    duration_error = av_mallocz(MAX_STREAMS * sizeof(*duration_error));
> > -    if (!duration_error) return AVERROR(ENOMEM);
> > +    last_dts            = av_mallocz(ic->nb_streams * sizeof(*last_dts));
> > +    duration_gcd        = av_mallocz(ic->nb_streams * sizeof(*duration_gcd));
> > +    duration_count      = av_mallocz(ic->nb_streams * sizeof(*duration_count));
> > +    duration_error      = av_mallocz(ic->nb_streams * sizeof(*duration_error));
> > +    codec_info_duration = av_mallocz(ic->nb_streams * sizeof(*codec_info_duration));
> > +    if (!last_dts || !duration_gcd || !duration_count || !duration_error ||
> > +        !codec_info_duration) {
> > +        ret = AVERROR(ENOMEM);
> > +        goto err_out;
> > +    }
> 
> possibly exploitable
> the number of streams can increase any time if more are found

"any time" makes it sound more serious than it is, within that
function I think it is only in av_read_frame_internal, so
after that call resizing the arrays may be necessary.
Still going to be a bit annoying to implement but not that bad.